Chapter 2, Professional Photoshop, 5th Edition

[Andy]

Chapter 2 - The Steeper the Curve, The More the Contrast


Writing curves is a form of horsetrading. Most improvements in the image come at a price. Fortunately, the price is sometimes quite reasonable. Look for areas you wish to emphasize, and then figure out how you will pay for that improvement.

Dan hits us over the head again with the orientation of the Curve - switch it so that the dark parts are upper and right. In CS2, you click on the gradient. In CS3, you hit the down arrow to show more details, and you select "pigment inks." If you do this, you'll be in sync with the curves illustrations in the rest of the book, and in all the reading group summaries. There's no sense really debating it - either you do it or you don't, it's entirely up to you :D

It's all About Contrast

When we view an image, our eyes are craving contrast. Images with good contrast are pleasing to us. Images with little or poor contrast, are typically described as "flat" "grey" "dull" or similar. This is not to say that you must have gobs of contrast in all images! But for the most part, most photos will benefit from it. Here on Dgrin, we've been calling it "Pop" and we have several good tutorials (http://dgrin.smugmug.com/gallery/2292454/1) that will get the new or learning Photoshopper on the way to using curves for better contrast.

Setting the Black and White Point

Dan doesn't talk about this much in this chapter, but it's what I usually do first. Here is an excellent method (http://dgrin.smugmug.com/gallery/2292454/1) of finding the important black and white points in your image. Remember, the chosen points may not be the darkest and lightest. Dan spends some time on "avoiding the catchlights" or what others call, the specular highlights. This is another reason why shooting in RAW, where we as photographers get to choose what's important, not some algorithm in the camera jpg, or in Photoshop's Auto Levels dialog. Why? If you set the endpoints to their very extremes (0 and 255 for example), you are for sure increasing contrast, but losing important detail in the highlights or shadows. How important that detail is, will vary by image, of course.

http://www.moonriverphotography.com/photos/119834978-S.jpghttp://www.moonriverphotography.com/photos/119834946-S.jpg

Curve Shape

Is an overall big ole S-curve always right? Well, it typically won't hurt, but it's not always best. The S-Curve will generally steepen (add contrast) to the midtones of the image. But what if the important areas are in the shadows or highlights? The typical S-curve does not improve these areas.

Curve Point Selection, and moving the curve. Click and hold, move your cursor around the image and when you have a point you want to plot on the curve, command-click it. NOW, when you want to move it, do as Dan says, and move it North-South only - use CTRL-TAB to move between the plotted points and the up/down arrows to now move (steepen) the curve. Thanks DavidTO, I've been seriously lagged in this department. Very precise, very easy.

Individual RGB vs. Master Curves

Margulis says that you'll often get better results by curving the channels individually. We'll see in later chapters. Dan says to avoid the master curve, that in CMYK it's a disaster, because K does not behave like CMY. OK fine, but we are photographers, and for most of us, we'll work in, and stay in, RGB curves. Still, Dan asserts that most images can benefit from individual moves in each channel's curve, rather than a master curve. I'm looking forward to having this lightbulb go off for me, personally, because I haven't yet found the pay-off in doing these curves individually (each channel separately). I'd love you to show me how!

So, in summary: Most images will benefit from added contrast. Use the curves tool to achieve this contrast. Taking control away from your camera (shooting RAW, or adding as little contrast in your in-camera jpgs as possible), and deciding what the important areas of the image are - this is what this chapter is about. Oh and don't forget the benefits of using the adjustment layers. You must get this concept now or you'll be hosed later. If you need to dial an adjustment back some, well, it's a cinch with the opacity of the adjustment layer! We'll use some of the techniques and fundamentals learned here throughout the book, and I'm counting on Dan to get that light bulb to turn on for me, with regard to "individual r-g-b curves will usually yield a better result."

The other thing I struggle with is that Dan's big on "global moves" and well, that's fine but I won't stick with global moves if there's a 60 second local correction or improvement that I can make. It's probably just that I'm accustomed to some ways that I've been using, and haven't yet gr0k'd the use of curves for a "local" improvement. I suspect this has to do with more sophisticated moves one will make with the curve, in different channels.

Some fun examples for us to play with in this chapter discussion thread. I'd love to see what you guys can do with them. They are unprocessed, except for converting from RAW. Click the thumbnails to get the original files.

http://www.moonriverphotography.com/photos/119623209-Th.jpg] (http://www.moonriverphotography.com/photos/119623209-O.jpg) http://www.moonriverphotography.com/photos/119679475-Th.jpg (http://www.moonriverphotography.com/photos/119679475-O.jpg) http://www.moonriverphotography.com/photos/119624359-Th.jpg] (http://www.moonriverphotography.com/photos/119624359-O.jpg) http://www.moonriverphotography.com/photos/119623189-Th.jpg (http://www.moonriverphotography.com/photos/119623189-O.jpg) http://www.moonriverphotography.com/photos/119834946-Th.jpg (http://www.moonriverphotography.com/photos/119834946-O.jpg)

[gefillmore]

http://gefillmore.smugmug.com/photos/119845484-L.jpg

I'm always wondering if this guy was crackin' wise with you when you took his pic-

adjusted curves separately in r, g and b channels and also the rgb-

[DavidTO]

I'd love to see someone (especially one of the color theory group guys) explain this whole adjusting the curves separately, and show how it's done, getting a successful version of one of these images. I gave up on it. It's beyond me at this point.

Anyone?

[Andy]

http://gefillmore.smugmug.com/photos/119845484-L.jpg

I'm always wondering if this guy was crackin' wise with you when you took his pic-

adjusted curves separately in r, g and b channels and also the rgb-I think you went too far. Lots of details lost, hair and shadows. And you made colors there that shouldn't be there (greens). This is my point about the r-g-b curves separate adjustments, how do you know? I'm not picking on you, George ...

This was my edit, just one master curve adjustment. I'm still waiting for an r-g-b curve that's better. Thanks George for contributing! :thumb
http://www.moonriverphotography.com/photos/119682829-L-1.jpg

[gefillmore]

no problem-

I don't get too concerned about shadows, but maybe I should-

and yeah, it's green-

back to the drawing board?-

is this where the adjustment layers come in, where you can adjust for colors and highlights and shadows?-

[Andy]

is this where the adjustment layers come in, where you can adjust for colors and highlights and shadows?-Well, according to Dan, we shouldn't have to do anything but global moves. Where' I'm stuck is in why/how r-g-b moves are better/easier than a single master curve move (which I did in my edit just above).

[gefillmore]

well, I eagerly anticipate the answer to this 'conundrum'-

[Richard]

Well, according to Dan, we shouldn't have to do anything but global moves. Where' I'm stuck is in why/how r-g-b moves are better/easier than a single master curve move (which I did in my edit just above).

Yeah, I am stuck at the same point. I understand his theoretical point--that master curve changes in RGB can distort colors--but since I don't have nearly the grasp of channels that Dan has, I generally seem to screw up the colors more when I try to muck with the individual channels. I do most of my work in LAB, though, where it is easier to separate color and contrast moves.

[jfriend]

Well, according to Dan, we shouldn't have to do anything but global moves. Where' I'm stuck is in why/how r-g-b moves are better/easier than a single master curve move (which I did in my edit just above).

I have played with per-channel moves and also can't get them to work the way he describes. The thing I don't understand about them is that unless you make the exact same moves in each channel (and then, what's the point), you are going to create significant color shifts in some tonal ranges. I find it way, way, way easier to do as Dan taught us in the LAB book and separate color from contrast. Make a contrast move with either an RGB curve in luminosity blend mode or an L curve in LAB mode and then make separate moves to adjust the colors either with R, G or B curve moves or A or B moves in LAB. In my normal workflow, I first get the global white balance right (either in ACR or with R, G or B curve moves), then enhance contrast (with a global curve), then decide if any finer grained color moves are needed (by shaping individual color channels).

When you are curving the R, G and B curves and trying to adjust color and contrast at the same time, it's either something only the Gods can do or it's just impractical and not nearly as easy as separating contrast moves from color moves like Dan taught us in the LAB book.

[edgework]

Well, according to Dan, we shouldn't have to do anything but global moves. Where' I'm stuck is in why/how r-g-b moves are better/easier than a single master curve move (which I did in my edit just above).

In theory, because the three RGB channels are of equal strength and equal values in all three yields dead neutral, master curves should simply darken and and lighten without shifting hue or saturation. It doesn't work that way. Darkening the Master curve pushes towards red. Setting a curve adjustment layer to Luminosity mode can ease that problem some, but there is still a red shift. Try it by taking a copy of the same image into LAB and pushing the lightness curve. Comparable moves in RGB will not produce identical results.

As for single channel moves, the point is to stretch the tonal range of each channel to maximize the full spectrum. Unless you are certain that the three channels are strong and deficient in the same ranges, a single, one-size-fits-all curve won't really fit any individual channel. The blue channel might need a boost in the shadow range while the red could need highlights stretched. No single Master curve can accomplish both.

As for global moves, I've always looked at it as Strategy vs. Tactics. Global moves are a sound strategy; if magenta is deficient in one part of the image, it's probably out of whack all over. But any general will agree that tactical requirements in the field trump stragegic planning every time. I like to work globally as much as I can, but sometimes a face needs different treatment. If the face is the point of the image, whether or not it balances perfectly with the background may not mean much. Ya gotta call 'em as you see 'em.

[DavidTO]

As for single channel moves, the point is to stretch the tonal range of each channel to maximize the full spectrum. Unless you are certain that the three channels are strong and deficient in the same ranges, a single, one-size-fits-all curve won't really fit any individual channel. The blue channel might need a boost in the shadow range while the red could need highlights stretched. No single Master curve can accomplish both.


Cool, I'd love to see it on that shot Andy has above of the man smiling at camera. The one the gefillmore took a whack at. I need to see someone do a channel by channel correction of that image that looks good. Like I said, I've given up.

[pathfinder]

I am so pleased to learn that I am not the only soul who has difficulty achieving good color and contrast balance by adjusting individual R,G, or B channels. I understand the theory, I think. I just find it rather hard to grok it out.

If I can find a black or a white or a good neutral, I can usually be confident of my results. But if they are not present, it gets much harder for me.

I too am more comfortable in LAB than RGB, and least comfortable in CMYK.

Here is my try at Andy's dog

http://Pathfinder.smugmug.com/photos/119928761-L.jpg

And his tailor

http://pathfinder.smugmug.com/photos/119928671-L.jpg

Not much editing needed by either of these shots though.

[kwalsh]

OK, so I went for the "What's the difference between composite and separate channels?" route.

Starting assumption: It's the guy's mug we care about. We want it to "snap" and so we want maximum contrast on his face.

Method: I don't want to dork with color, so it is an adjustment layer set to luminosity mode. Somewhere in the first few chapters Dan mentions many of his students do curves twice, once for contrast and once for color using the luminosity and color blend modes. Since chapter 2 is just on contrast I'm using the luminosity blend. Side note: If you think a composite curve doesn't effect color go ahead and click "luminosity" and be surprised just how much it changed the color!


So, set white and black points by moving the top and bottom of the curve and check "show clipping" and wait for something important to clip. In composite mode you can't do much, in per channel you can move 'em a lot.

Next, examine the face with the dropper and see where it lives in the curves. In composite it lives mostly above the 1/4 tone and is spread all over the place. In per channel it is in the middle for blue and near the middle top for green and very near the top for red. So blue will be an S and red and green just exponentials.

A word of apology, I forgot to flip the curves into "Dan" mode so they are backwards for all ya.

Final Results: I got a fair bit of contrast with both - but I couldn't get the composite curve to give me as much as the per channel. It always ended up either biased light, dark or if I did an S lost a lot of contrast. What I've posted here was about as much contrast as I could and ended up a bit light compared to the per channel.

Here are the curves:

http://kenandchristine.smugmug.com/photos/119936285-L.jpghttp://kenandchristine.smugmug.com/photos/119936317-L.jpg

Here is the full frame with per channel curves:
http://kenandchristine.smugmug.com/photos/119936432-L.jpg

Here it is with composite:
http://kenandchristine.smugmug.com/photos/119936128-L.jpg

And since the face is what I'm intersted in, left is per channel, right is composite:
http://kenandchristine.smugmug.com/photos/119936182-L.jpghttp://kenandchristine.smugmug.com/photos/119936256-L.jpg

So here it seems to me the face does have higher contrast while holding detail in the shadows and highlights. Unfortunately I couldn't get the composite to exactly match the brightness of the per channel without it going flatter on me. I'm not sure if that's a function of the difficulty of a composite channel or me just not being good enough.

So, in conclusion, I'm starting to get what Dan means here. I just don't think I'm clever enough to do contrast and color simultaneously and it sounds like lots of his students don't either! Are the differences here super drammatic? No, but I'm not sure much of this is (short of the LAB tricks that is). Anyway, hopefully this sort of illustrates using per channel curves, even if it is my inept first attempt.

Ken

[jfriend]

So, in conclusion, I'm starting to get what Dan means here. I just don't think I'm clever enough to do contrast and color simultaneously and it sounds like lots of his students don't either! Are the differences here super drammatic? No, but I'm not sure much of this is (short of the LAB tricks that is). Anyway, hopefully this sort of illustrates using per channel curves, even if it is my inept first attempt.

In the LAB book (I don't remember which chapter), Dan does suggest exactly the technique you used here - adjusting each R,G,B curve separately in the luminosity blend mode. I've found it to be a useful technique for contrast enhancement on some particular types images. In fact, it's even better than an L curve in LAB mode on some images.

The best I can tell, the images that it works uniquely well on are ones where the R, G and B channels all peak in very different locations, thus you can't target a single area of the composite curve to steepen and not miss a lot of interesting pixels, some of which you care about. Furthermore, when one of the areas you're trying to enhance contrast is pretty bright or pretty dark, it seems like it's easier to steepen a particular color channel in that region without throwing off the rest of the image as much as doing so in the composite channel causes.

From what I've read (and remembered) in this new book, I don't see Dan recommend using the Luminosity blend mode with his color channel moves. He seems to just have at it directly on the color channels, somehow doing simultaneous moves in color and contrast. I'm sticking to one at a time. Much more predicatable, quicker and more reliable for me. I don't think there are any disadvantages to separating the color and contrast moves either.

[kwalsh]

The best I can tell, the images that it works uniquely well on are ones where the R, G and B channels all peak in very different locations, thus you can't target a single area of the composite curve to steepen and not miss a lot of interesting pixels, some of which you care about. Furthermore, when one of the areas you're trying to enhance contrast is pretty bright or pretty dark, it seems like it's easier to steepen a particular color channel in that region without throwing off the rest of the image as much as doing so in the composite channel causes.

Yes, this is definately true I think. I don't think the doggie in the snow is going to have any help from per channel curves. Human faces on the other hand seem to be a reasonable target. I think accordian man will be problematic since we need to preserve the accordian - perhaps that'll be a CMYK with the K curve for the accordian. Yosemite belongs in LAB for sure.

One visualization trick if the whole mouse over the subject and watch where it lies on the curve thing doesn't do it for you. On the adjustment layer do each channel one at a time. Before doing the curve for a channel go to the channels panel and show only that channel. That way you'll basically be doing curves for three separate B&W images. Might be easier to digest at first.

Ken

P.S. I need to read the LAB book again too...

[rutt]

I'm in Italy until middle of next week and have only the most unreliable internet connection (thanks to tin.it)

Hey, Andy, good job. That's what I like to see, explain what you get, ask questions about what you don't get. Provoke discussion.

I've come to see RGB curves as an advanced technique. LAB curves are much easier. The L curve does just what you expect for contrast and the A and B curves make big color moves pretty easy. Combine with blend-if sliders and you get a lot of control pretty easily.

If you do need to work in CMYK, you just have to use the curves to adjust the shadows by steepening the dark end of the K curve and removing some of the other colors from the shadows (yellow in particular.)

RGB curves, on the other hand, are a less important tool in my box. My most frequent use of them is to adjust skin tones. I just did one, but I don't hink I can post. But when flesh is more magenta than yellow, make a curves layer, pull up the blue curve, find out where the magenta flesh tones live on the curve and pull the curve up just a little there (toward darkness). By darkening the blue, you are lightening the yellow and bringing it back into balance. Because you only change the curve where the fleshtones are, you have less chance of changing neutral points or the color in other parts of the image. Once you are done getting the flesh right, you can set the blending mode of the curve layer to "Color" and it won't effect contrast. Of course, since you have only played with the blue curve, it will have only a 10% effect on contrast, right?

Dan has plenty of examples with individual channels in RGB curves being particularly important. I'll scan through the book and cite some of them.

The white dog is like the most classic example of something I would do in LAB. The first class of Dan's we did an image of some white seals. We did it three times, once with CMYK curves, once with blending, and finally with LAB curves. The point was that LAB curves and sharpening did the best job easiest by far of keeping the neutral neutral.

[Andy]

Looking at Ken's and PF's edit, with r-g-b individual curves, I don't see an improvement over the master curve adjustment. I see loss of detail, too much contrast, and too much saturation.

I'm going to continue to be patient though, and wait for it to hit me like a ton of bricks :D

[kwalsh]

Looking at Ken's and PF's edit, with r-g-b individual curves, I don't see an improvement over the master curve adjustment. I see loss of detail, too much contrast, and too much saturation.

I'm going to continue to be patient though, and wait for it to hit me like a ton of bricks :D

Well I don't think there is any loss of detail in either the composite or per channel edits on my two images. Actually the detail is greatly enhanced because of the (excessively?) enhanced contrast.

I'm totally with you on the no huge difference between the two. Of course a lot of the differences between images in the book are pretty subtle as well. I too have yet to be hit with a ton of bricks :D.

As far as too much contrast goes, I'm not going to argue with you there. I was just taking Dan's "emphasize contrast on the subject" concept to the maximum. I'm not sure we really want to do that to this poor guy!

Taking another card from Dan's deck and over doing something and then dialing it back here is the per channel with the opacity dialed back to 50%:

http://kenandchristine.smugmug.com/photos/120004580-L.jpg

I greatly prefer this one to any of the previous posts. My ultra-high contrast ones are just too dark. Comparing this version to your's and PF's the face has much more depth and shape to it and he is set off from the background better. That said, too each their own! And now with it dialed back to 50% it would seem there would be even less difference between this and a composite curve. Probably need some more dramatically colored image to see a big difference.

Anyway, still playing and reading and looking around expectantly for bricks...

Ken

P.S. Great image, by the way.

[edgework]

Aside from an overall lightness in the shadows, the entire image feels too red. On first reading, the skin tones seem okay from the numbers. The biggest problem is that the face is flat. The only real variation in detail comes from the blue plate, which includes a host of skin imperfections that makes it unacceptable for use in plate blending.

The shadows in the clothing are weak, but also red; ideally, you would push towards neutral as you darken in areas. The most telling feature is his hair. Maybe he's still got light brown hair, but I'd bet that he's closer to grey than the numbers suggest: 36C 37M 43Y doesn't suggest light brown to me so much as a red cast.

The curves I used push the cyan element with a larger bulge in the Red channel, and pull all three down in the highlights, to bring out more detail in the face. I focused on different areas of the face which, predictably, has a variety of tones and hues, tweaking curves in the Green and Blue channels to keep either magenta or yellow from dominating. I added cyan by pushing the Red curve in the shadow areas in the clothing, and in the dark lines of his face, which you want to keep from going hot. Most of those shadows were in the cyan midtones, with the exception of the dark suit to the right of the image.

As it happens, without actually measuring any of the hair, it now looks a good deal grayer. Also, the shadows have pushed more towards neutral without losing the brillance of objects that are truly red, green and yellow. Note also, the increased detail in the red plaid at the left of the image.

(Since this is about curves, I avoided the big gun in face balancing: Selective color, with a slight subtraction of Magenta and addition of Yellow to the Reds, and a subtraction of Yellow and addition of Magenta to the Yellows).

http://idisk.mac.com/crawfordhart-Public/wiseguy.jpg


And, following the "Rule-of-75," which states that any move that looks good upon completion, will look much better the next day if you first pull the change back to 75% of its original intensity, we get this version:

http://idisk.mac.com/crawfordhart-Public/wiseguy_75.jpg

Another move I avoided, but which I ordinarily always use, is to make a fake black adjustment by copying the image, converting to CMYK and then using the black channel as a layer maske for a luminosity curve (the master curve works fine for this), adding weight to shadows in a much more subtle way than a raw Master curve could accomplish.

These are the three curves I used:

http://idisk.mac.com/crawfordhart-Public/curves.gif

[Duffy Pratt]

I own Samoyeds myself, so I ordinarily would have done the Samoyeds in LAB. For this, I did it in RGB, partially because I thought there was a slightly moving cast on the dog. I decided to neutralize the bluest parts of the dog, and let the snow go even more blue. I also picked the top of the dogs nose as the shadow, but set it's black point to a very conservative 30,30,30. For the white point I took the lightest point on the nose and set it to 245,245,245. This adjustment here is only the RGB curve, done by individual channels.

For the smiling man, I did a CMYK curve. The black point was basically a guess, and I was willing to be flexible on it. I decided on the sleeve of the jacket behind the window. The white point was the lightest part of the man's hair. The biggest problem with this picture was the excess magenta in the skin, and the big color variations in the skin as well. Again, this is just a CMYK curve and nothing else.

On the general issue, its been important for me to write curves on the individual channels even in the easy cases where a master curve could do, largely for practice and to learn. When things go haywire, I can always retreat to easier methods, but I find that things go haywire less often the more I try to use the methods Margulis recommends. And overall, the results seem to be better for me.

Duffy

[Duffy Pratt]

Can only upload one file at a time, it seems. This is the tailor done in individual CMYK curves, as discussed above.

Duffy

[DavidTO]

Can only upload one file at a time, it seems. This is the tailor done in individual CMYK curves, as discussed above.

Duffy


You can use IMG tags to put more than one pic in a post, but yes, attach is one at a time.

Check out the link in my sig for a how-to.

[jfriend]

RGB curves, on the other hand, are a less important tool in my box. My most frequent use of them is to adjust skin tones. I just did one, but I don't hink I can post. But when flesh is more magenta than yellow, make a curves layer, pull up the blue curve, find out where the magenta flesh tones live on the curve and pull the curve up just a little there (toward darkness). By darkening the blue, you are lightening the yellow and bringing it back into balance. Because you only change the curve where the fleshtones are, you have less chance of changing neutral points or the color in other parts of the image. Once you are done getting the flesh right, you can set the blending mode of the curve layer to "Color" and it won't effect contrast. Of course, since you have only played with the blue curve, it will have only a 10% effect on contrast, right?

I agree that I use individual R,G,B curve manipulations all the time when I am trying to tweak color, particularly skin tone. But, I'm not ready to use individual channel moves for tweaking contrast unless I've got them in luminosity blend mode. I really bought into the concept of separating contrast from color in Dan's Lab book as it really, really seems to simplify things and I'm not aware of any quality or flexibility sacrifice for that simplicity.

[Nikolai]

Great job on the chapter! :thumb
Speaking on per-channel curves and such...
1) I understand that master RGB/CMYK curve may, and most likely, will shift the colors. Hence - adjustment layer in luminosity mode or immediate Fade-Luminosity.
2) I also understand that a cleaner, yet still rather simple, way to do a basic curve work is doing it in L channel (adjustment layer or not)
3) What I do not get, not at least at my "spine brain" level, is how Dan comes to all those very particular and very different per chanel curves.
I mean, change any one channel - and your colors are shifted all over the board. He speaks of trade off, and that's exactly what we get here: if we improve the color/contrast/perception in one area, we inevitably lose something (shift color, for instance) in some other area, or, most likely ALL other areas of this image..

At this point I'm kinda in boat with Andy: if I need to do something curvy in one particular area and I do not want this change to affect the rest of the image - I simply do it via selection, or, actually, on a separate adjustment layer (which has mask by default) in a luminosity mode.

PS. I'm 40% done with my chapter (6, sharpening), hope to be ready soon.

[Andy]

Granted, this may not be the best example shot (Tailor-man) but I'm not convinced yet by anyone that individual moves are worth it.

[edgework]

Granted, this may not be the best example shot (Tailor-man) but I'm not convinced yet by anyone that individual moves are worth it.

If you feel that the image has no cast, then a contrast move is all that is called for. If there is a cast, then the Master curve will simply enhance it.

[AZsnapper]

Since reading this book, I have been trying real hard to only do per channel adjustments, and use the Shadow/Highlight tool a little bit.

I find the per channel works rather well if I know there are true blacks, whites, and neutrals in the image. But it can sometimes get a little frustrating.



If you feel that the image has no cast, then a contrast move is all that is called for. If there is a cast, then the Master curve will simply enhance it.

[Andy]

If you feel that the image has no cast, then a contrast move is all that is called for. If there is a cast, then the Master curve will simply enhance it.
Heheh I'm actually tired of him (the suit-seller), I originally processed him in BW and I really like him best that way... :lol3

[kwalsh]

I've played with a few more of my images and re-read the contrast chapter. A few things I've noticed:

1. It is very hard for me to do different curves per channel without using a luminosity blend. I'm definately not talented/experienced enough to do color and contrast at the same time.

2. In the end I haven't found an image that I see a drammatic difference between per channel and composite curves. HOWEVER, for me at least this has only been true when I do the per channel first and then play with the composite. I definately find it easier to create maximum contrast on the subject using per channel curves and luminosity blend. After doing this I can usually pull off a composite curve that does nearly the same thing. I have trouble eeking that much contrast out of the subject just starting with composite blind to the real possibilities in the image. That said, I rarely actually want that much contrast and I dial back the layer quite a bit. IN THE END, at the contrast levels I want if I really search for it I can see a very minor benefit in the per channel curves, nothing major.

3. Reading through what Dan says in the chapter I think perhaps some of our perplexity results from us doing RGB curves. It sounds like the master (i.e. composite) curve in CMYK is what really needs to be avoided ("disasterous" in Dan's words) because in that case the black channel really is totally unlike the others and almost always must be handled differently. He states in RGB this isn't as much of an issue except for a less "optimal" handling of contrast and the bigger issue of color and saturation shifts. I'm thinking composite curve with a luminosity blend is probably the fastest solution.

4. Now that I am aware of it I'm quite amazed at just how much the composite curve can freak out color and saturation. It think it definately should be used with a luminosity blend. It also makes me fear whether I'll ever get curves to work on color and contrast simultaneously. Composite seems so benign and yet it can really screw with the image.

5. With regards to the "trade off" Dan does address this in one of the early chapters. He basically says yes, you may freak out other colors with your curves. That is only a problem if those colors actually exist in the image you are working on. He's got an example (I believe it is the purple dress again) with a macbeth color chart in it. In his curve setup a lot of the colors on the chart go wacko. So what, they aren't part of the image. I think his point is if there is one dominant color in the image you are going to need to expand it (sort of like LAB does) to match the eye's simultaneous contrast and in doing so you are going to trade in screwing up a lot of other colors. That's OK if those colors aren't around to begin with.

Ken

[Duffy Pratt]

The by-the-numbers approach doesn't care about color shifts unless it does one of the following:

1) Kills neutrality in obvious neutral areas
2) Throws known colors out of whack; or
3) Makes something in the image have an impossible color.

From this perspective, there is a great deal of leeway for most things in most images. In the tailor shot, take a look at the yellow shirt in the right of the various submissions. No one knows what color yellow that shirt is. We do know it is not the color in the original picture, because of the cast in the entire picture. So how much of a move makes a color shift to that shirt untenable? This is a question on which one can disagree.

The samoyed shot, for the same reason, is much harder to color correct. Snow is white, and so is the dog. but if you look at the original, the snow is anywhere from -4 to -8 in the B channel, while the dog is anywhere from -3 to 4. That's a fairly big spread of 13 points in the B channel for stuff that is all supposed to be neutral. To make matters worse, it doesn't appear to me that the variation can be explained by light and shadow. On this picture, I just decided that people can live with blue snow, since all sorts of shots have that as a convention, and because the dog is the subject of the picture. But blue fur is a big no-no. So I killed the blue in the fur and generally cooled the picture. With more time, I might try to kill the cast in the snow and the fur, neutralizing them both, while retaining the brownish red in the dog's eyes and on his nose. That takes techniques that are outside the scope of this chapter, but its not that hard to do.

Duffy

[rutt]

OK, Andy, you question two of Dan's points:

Prefer global moves (curves, blending, sharpening, that sort of thing) over local ones (selections, painting, burning, that sort of thing.)
Superior results are possible with by writing a separate curve for each channel than by using the master RGB curve.

These are both excellent questions. I think the answer to 1. should wait until we've absorbed more of the book. When only a local move works, Dan doesn't hesitate to make it, but he accomplishes a surprising amount without doing so and mostly it is easier (once you know how!) and looks better.

The second question requires some careful parsing. If you know how to write individual curves, you can achieve superior results for most images. Sometimes the difference is very subtle, especially when a single color is most important, as in portraits and especially on a monitor as opposed to in print. How much better is Dan's waterfall with individiual curves than with the master curve? A little. How much better is Dan's image of the mountain in the mist with the individual curves than the version with master curves. A lot, I think. At least a lot by Dan's standards (remember, this is a competitive sport for him.)

I found an example where I could do a lot more with individual RGB curves than with the master curve. Here is the original:

http://rutt.smugmug.com/photos/120614288-L.jpg

With a master curve adjustment to set a light point in the stone just in front of the chestnut pan and steepen through the subject (face, shirt, fruit, chestnuts, apron; this is a busy image:

http://rutt.smugmug.com/photos/120613725-L.jpg

http://rutt.smugmug.com/photos/120632940-S.jpg

With individual curves, I was able to steepen each element of the subject more carefully without blowing or plugging other parts:

http://rutt.smugmug.com/photos/120614445-L.jpg

http://rutt.smugmug.com/photos/120632952-S.jpg

Now the chestnuts, fruit, shirt, apron, and face all pop better. [No plate blending, here. No sharpening. No LAB or CMYK. No exposure compensation. I'm just trying to compare apples to apples re master vs individual RGB curves.

If you only use the master curve you are limited to fairly simple forms of horsetrading. Often that's fine. But learning to use the individual curves can pay off by letting you squeeze a little extra contrast here without having to pay for it there.

Others have already pointed out that using individual curves works better when you are fighting a cast or want to change the color balance in some way. We can all agree on that, but that's not what this chapter is about. Dan's point here is that you may be able put together a complex trade that doesn't really lose anywhere in order to pay for it's improvements. But, the best examples of this are going to be "busy" images.

It was interesting to read this chapter again today. RGB curves are an elementary tool in Dan's box, but this particular application isn't my most common use for them. These days I do a lot of channel blending to try to bring out contrast and use RGB mosty in color mode to correct color balance. But Dan's images of the waterfall and especially the Chinese landscape show just how far this technique can take you if you are willing to think about the channel structure before starting to write curves.

[rutt]

And just to prove the point about the power of blending, I used a very simple blend here to give me a better starting point for my RGB curves: I used the green channel as for a luminosity blend. Then I got this:

http://rutt.smugmug.com/photos/120644890-L.jpg

with these curves:

http://rutt.smugmug.com/photos/120644505-S.jpg

So my point: hang on, there is a lot more fun to be had. Learning the how the individual channels contribute to both color and contrast opens the door to all kinds of entertainment.

[Myer]

And just to prove the point about the power of blending, I used a very simple blend here to give me a better starting point for my RGB curves: I used the green channel as for a luminosity blend. Then I got this:

http://rutt.smugmug.com/photos/120644890-L.jpg

with these curves:

http://rutt.smugmug.com/photos/120644505-S.jpg

So my point: hang on, there is a lot more fun to be had. Learning the how the individual channels contribute to both color and contrast opens the door to all kinds of entertainment.

= = = = = = = = = =


I think there are some basic issues I have.

I just spent 3 months adjusting my brain to LAB and that's how I now think. Which colors in which channels. What makes different parts of each channel lighter and darker, etc.

Now we find ourselves on a different book. Why? Well, we are either loyal to our new found knowledge in LAB or the author who seems to have abandoned (to now) much of what we learned in the LAB book.

Dan is very comfortable with LAB, RGB and CMYK. He switches from one to the other, what makes up various colors, what causes a channel to become light or dark, which number in which color space are increases or decreases in both/either color intensity and or light/dark.

I can see myself (I'm somewhere in Chapter 3) going back to the diagrams that explain the color relationships (I think in Chapter 1). Then I will create a new image that contains rectangles with about 10 basic colors. I want to switch between LAB, RGB and CMYK to see the values (numbers) and which channels become light and dark and when.

Dan very quickly mentions at one point "Brown - Oh that really some type of Red". I don't think that quickly. That's why I'm going to play with colors in LAB, RGB and CMYK.

Another problem I'm having is seeing flaws in images that he sees. I look at an imgae. If it looks very good to me, I find it difficult to play with since I'll probably make it worse and not better.

As someone else mentioned, much of the time I immediately think of how to improve the image in LAB since that is now my approach of choice.

I really like the idea of being able to separate Luminoscity from color. I can concentrate on one thing at a time.

An example of the two approaches. An image with a bluish-green cast. Dan is now suggesting we darken the Blue channel. He used an opacity of 65% (app). How he knows that is beyond me.

In LAB I merely move the exact portion of the b channel down (I place several holders above and below the spot to restrict movement). Also the a to reduce the green.

I've learned a lot of peripheral things in the LAB book. Creating and using channel masks and applying image has been fantastic. I check the RGB channels to channels to copy as masks as they have much more contrast in them than LAB channels.

I too have almost cheated in RGB. By using a Luminoscity Layer in RGB you are actually simulating LAB by separating Luminoscity from color.

I won't give up on Dan even if I may or may not use a lot of his approaches. The peripheral things learned alone are worth it. What I'm going to do is stop going frontwards and backtrack to become more comfortable in the workings of RGB and CMYK.

Way too long. Comments?

[rutt]

The LAB book is about the power of LAB. For something that seems so counterintuitive at first, LAB turns out to be a really easy colorspace once people get their minds around it. If you are going to master just one photoshop book, master Photoshop LAB. You get by far the most bang for the buck.

This book might best be called "10 Channels". We are still pretty far from the real payoff here, which I think is channel blending and sharpening. I have been to three of Dan's classes: the introductory class and two advanced classes. These are very competitive affairs. The format is like this: Dan gives an hour or two long lecture/demo. Then he assigns a set of about 5 images and everyone takes a few hours to correct them all. Then the class gathers together and compares all the versions, ultimately choosing a favorite of each. Dan always shows his version and one or two "ringers" from previous classes.

The LAB techniques alone will often get you to the semifinals of these competitions but rarely win them. I think the same is true of solid understanding of RGB curves and sharpening. No single set of techniques consistently produce the best images.

I am a computer scientist and got interested in Dan's techniques at least in part because I thought I'd be able to write a computer program to make them more accessible to a wider audience. It turned out that the simplest techniques (the basic LAB curve recipe, e.g.) were so easy that almost anyone could learn them and they do in fact make a huge difference. But the more I learned, the more confused I became about how to package in a user friendly way the enormous tool box that someone like Dan uses. As you read this book, keep a little notebook and note down all the different approaches he uses. Try to understand how he chooses which approach. The interplay technique and aesthetic judgment actually mindblowing. Near the end of the book (which I don't have with me) there is a little flowchart where he tries to explain how he goes about making these decisions. Skip ahead and take a look. It might help.

Meantime, try to relax and enjoy the book. It's still very early in the process. Once we get to chapter 5 you'll start to feel that there is something going on here that will take you beyond what you can do with just LAB techniques.

[Myer]

The LAB book is about the power of LAB. For something that seems so counterintuitive at first, LAB turns out to be a really easy colorspace once people get their minds around it. If you are going to master just one photoshop book, master Photoshop LAB. You get by far the most bang for the buck.

This book might best be called "10 Channels". We are still pretty far from the real payoff here, which I think is channel blending and sharpening. I have been to three of Dan's classes: the introductory class and two advanced classes. These are very competitive affairs. The format is like this: Dan gives an hour or two long lecture/demo. Then he assigns a set of about 5 images and everyone takes a few hours to correct them all. Then the class gathers together and compares all the versions, ultimately choosing a favorite of each. Dan always shows his version and one or two "ringers" from previous classes.

The LAB techniques alone will often get you to the semifinals of these competitions but rarely win them. I think the same is true of solid understanding of RGB curves and sharpening. No single set of techniques consistently produce the best images.

I am a computer scientist and got interested in Dan's techniques at least in part because I thought I'd be able to write a computer program to make them more accessible to a wider audience. It turned out that the simplest techniques (the basic LAB curve recipe, e.g.) were so easy that almost anyone could learn them and they do in fact make a huge difference. But the more I learned, the more confused I became about how to package in a user friendly way the enormous tool box that someone like Dan uses. As you read this book, keep a little notebook and note down all the different approaches he uses. Try to understand how he chooses which approach. The interplay technique and aesthetic judgment actually mindblowing. Near the end of the book (which I don't have with me) there is a little flowchart where he tries to explain how he goes about making these decisions. Skip ahead and take a look. It might help.

Meantime, try to relax and enjoy the book. It's still very early in the process. Once we get to chapter 5 you'll start to feel that there is something going on here that will take you beyond what you can do with just LAB techniques.



= = = = = =

I think I may have conveyed the wrong idea. I'm not frustrated by the new book. I find it very interesting. Just like the LAB book, I don't read more than a few pages at a time. Then I circle back and reread.

It seems he's speaking faster than I understand. I'm way more comfortable in LAB, getting a bit more comfortable in RGB and still a ways to go (long way) in CMYK. For simplicity, I'm thinking of ignoring CMYK but I'm concerned it may hamper me in the book.

You are correct that the title should have been "10 Channels".

I'm just going to spend a few days reviewing colors, values, channel lighter and darker and how various colors are produced (the ones that are not directly geen/magenta/blue/yellow or red/green/blue, etc.

I wonder if any other books are reviewed in this way?

[Duffy Pratt]

It's funny, I take the opposite approach. I just finished my first reading of it, without doing any of the examples. Now I've dived into a second go round, this time straight through while using the CD to mimc the examples. I figure on the third go round, some of the harder things might start seeping in.

That's how I did the LAB book, and unlike everyone else, I don't see anything unintuitive about LAB because that book is the first serious color correction book I ever used. I followed some Kelby recipes in Elements before that, but I started thinking about color correction in LAB.

Also, once the separation is done, I have found it much easier to write curves in CMYK than in RGB. And its interesting: I've always found it much easier to set the black point in CMYK and conversely for some reason I have an easier time setting a white point in RGB. Not sure why that is, but it almost always seems to be the case.

The book could have been called 10 channels, but I think even that is unfair to Dan's approach. Having read his stuff, I would love to be able to get a working HSB space, because I can already envision how you could do great things with an S plate, even though I've never actually seen one. Because I think you could apply his methods to other color spaces than the three he uses, I don't think its really fair to limit the book to even 10 channels.

Duffy

[edgework]

...I would love to be able to get a working HSB space, because I can already envision how you could do great things with an S plate, even though I've never actually seen one. Because I think you could apply his methods to other color spaces than the three he uses, I don't think its really fair to limit the book to even 10 channels.

Duffy

Here's a quick formula for producing an S plate.

Create a Selective Color adjustment layer.

For each of the six color options (Red, Yellow, Green, Cyan, Blue, Magenta) pull the Black slider all the way to the left (-100).

For the three neutral options (White, Neutral, Black) pull the black slider all the way to the right (+100).

Copy Merged.

Paste into a new channel. Saturated tones push towards white, desaturated towards black.

As for Hue and Brightness, I can imagine that Brightness would be somewhat like the Lightness channel, but I couldn't imagine what the hue channel would look like; similar to the a and b channels, but with the entire spectrum encoded between black and white. No idea how one would create it.

[Duffy Pratt]

Thanks for the tip. The only thing you left out is to make sure that you select absolute instead of the default "relative". Otherwise you don't end up with a black and white plate. This one probably deserves an action, because I can see lots of places where it would be useful to have this for masking purposes alone. Thanks again.

Duffy

[edgework]

Thanks for the tip. The only thing you left out is to make sure that you select absolute instead of the default "relative". Otherwise you don't end up with a black and white plate. This one probably deserves an action, because I can see lots of places where it would be useful to have this for masking purposes alone. Thanks again.

Duffy

Should also point out that it only works in RGB, though that would be obvious if it was attempted in CMYK.

[ginger_55]

Obviously I have not read this chapter. I am barely reading two pages a day in my Greg Iles novel.

But I read a lot of this thread yesterday. (I do part of my work in LAB, but I tend to "think" in RGB).

So, last night/early AM, I was working away in selective colors when a lightbulb went off.

No, I would not have rather been in curves. I wanted to work w individual colors. Now that is not like your stuff, Rutt, but it is also not a "master" approach. I do the "master" thing first, then go from there, usually.

Also, just coming back to check out this thread, I noticed that mention is made that Dan said something about the color "brown" being a something of "red". I noticed that months ago.

Am I somewhat smart, here, :barb , or just too dumb and ignorant to know what you all are really talking about?:rolleyes

ginger (and I like emoticons at times!!!) Can't read the bk this am, am checking messages, then have to shoot two baptisms, for free.

[gefillmore]

rutt: 'Meantime, try to relax and enjoy the book. It's still very early in the process. Once we get to chapter 5 you'll start to feel that there is something going on here that will take you beyond what you can do with just LAB techniques.'

I am finally getting a little time to get into this-

although I am more a pragmatist than a detail person (lazy? attention deficit? unorganized? I dunno; just the way I am) I am beginning to find this interesting and am looking forward to delving into this book more-

and besides telling all this, I wanted to bump this thread-

[erich6]

There's another aspect of individual RGB curve adjustments that hasn't been discussed yet and maybe the root cause of why individual adjustments are "technically" more accurate. Note that the key thing here is *accuracy* which may not ultimately lead to a better photograph.

When a CCD or CMOS sensor converts light into electrical signals that get digitized it does it by the photoconversion effect. If you remember from your physics classes light is energy and is quantized by photons. Photons get converted to electrons by silicon imaging devices and it is the number of electrons that generates the signal levels that get digitized.

Because Blue photons are more energetic than Red it takes more red photons to generate the same number of electrons. So for an equal distribution of brightness between blue and red you will get different signal levels from the CCD for each channel.

Because Red, Green, and Blue channels are basically filtered pixels of the same CCD it is likely that the camera makers don't have individually adjusted gains which is why you will get brightness levels for each portion of the spectrum mapped to different portions of the pixel digital scale.

When you apply a composite curve to an image it applies the same tone transfer to all the channels. So, if you have a particular color mapped to lower pixel counts it will see the knee of the curve while another color mapped to the higher pixel counts may see the shoulder of the curve. This results in a color shift.

My guess is that Dan is making the case that you want to individually adjust each channel so you get the right distribution of color counts across the tonal range. I think it's rather difficult to get a feel for this but it can be done. In the end, I find it more intuitive to adjust the tonal ranges for each color and then apply a master "composite" curve adjustment. If you did the individual R,G,B adjustments correctly you should see NO difference between the composite adjustment in "Luminosity" mode vs. "Normal" mode because you effectively adjusted the colors so they are proportional with Brightness (i.e., luminosity).

Here's Andy's street shot adjusted as he did with a "composite" master curve adjustment:

http://www.moonriverphotography.com/photos/119682829-L-1.jpg

Here's my cut using individual RGB adjustments:

http://hbphoto.smugmug.com/photos/125452114-L.jpg

I think you'll be hard-pressed to make a definitive call between the two.... The preference here will likely be more of a function of individual tastes and other aspects of post-processing are going to be more of a deciding factor.

The Yosemite shot is a different story. Here's what I got when I adjusted the original file with a "composite" master curve adjustment (I even used the black and white points Andy defined in the file):

http://hbphoto.smugmug.com/photos/125451789-L.jpg


Here's what I got when I adjusted each RGB channel individually:

http://hbphoto.smugmug.com/photos/125451697-L.jpg

While both shots could benefit from localized adjustments the individual RGB adjustments resulted in trees looking GREEN as they are supposed to. The rocks also have a better tonal range.

Erich

[jfriend]

There's another aspect of individual RGB curve adjustments that hasn't been discussed yet and maybe the root cause of why individual adjustments are "technically" more accurate. Note that the key thing here is *accuracy* which may not ultimately lead to a better photograph.

[snip]

While both shots could benefit from localized adjustments the individual RGB adjustments resulted in trees looking GREEN as they are supposed to. The rocks also have a better tonal range.

Erich
I'm sorry Erich. I just don't follow your argument that using individual color curves has something to do with how the sensor works. As for your two image corrections, I don't see that yours are clearly better.

In the image of the man, you end up with different colors (the shirt and facial colors are different). It's 100% opinion whether yours are better colors than the one from the master curve.

In the image of Yosemite, you might have different tree colors, but the first image has much better detail in the background and waterfall. Although I wasn't actually there when this Yosemite picture was taken (so I don't know what it's supposed to look like), you might be surprised to find that the original could be closer to reality. Forest trees are often more yellow than they are green (the same is true of grass). Yours looks way to green to me.

I still don't understand why manipulating individual color curves is better than separating color from contrast in LAB or using the color and luminosity blend modes to separate color from contrast in RGB.

[erich6]

In the image of the man, you end up with different colors (the shirt and facial colors are different). It's 100% opinion whether yours are better colors than the one from the master curve.


I agree...I said the same thing in my post. I think for the shot of the man there are going to be other factors that will make a bigger difference in the way the final image comes out.

In the image of Yosemite, you might have different tree colors, but the first image has much better detail in the background and waterfall. Although I wasn't actually there when this Yosemite picture was taken (so I don't know what it's supposed to look like), you might be surprised to find that the original could be closer to reality. Forest trees are often more yellow than they are green (the same is true of grass). Yours looks way to green to me.

Yeah...I noticed I didn't fix the highlights to keep from losing tonal range in the waterfall. I didn't spend a lot of time on the shot...simply trying to illustrate the concept.

I'm not arguing that you have to do RGB individual adjustments to get a good image in post-processing. I never do that myself in my workflow. I was just trying to point out why theoretically this would be the most accurate way of doing it. Personally I don't find it to be practical....

Erich

[JettyJ]

I think one thing that is tripping people up is that curves in individual channels has a much more profound effect when you have an image that needs serious correcting (colors are inaccurate, unbelievable, or just 'off') - Images that have mostly 'correct' colors from the start need more enhancing than correcting and probably be done with a master curve or a quick trip to LAB for some boost.

Somebody else has already said it but the point is that each image has 10 channels (R,G,B,C,M,Y,K,L,A,B) and each one of these channels has more or less detail than any of the others. Try not to take the individual corrections in the book so literally and try to start thinking about what each channel looks like in an image. Once you become proficient at that (and I am definitely not) you can use the techniques he talks about to pull the best detail from the best channels and use those to get the image you are after.

[rutt]

Try this as both a thought experiment and an actual one. Make a curves adjustment layer, but set the blending mode to "luminosity". Now, you can't do anything with the curves which will change the colors, only the contrast. So we are only thinking about contrast.

What additional control can you get at this point from using the individual curves over what you will get from just the master curve? Well, you can adjust the contrast of very blue things separately from that of very red or green things. It's very similar to making a good B&W. Once you convert you've lost information which may be useful. Similarly, using just the master curve loses the chance to address the contrast of different colors separately.

[jfriend]

Try this as both a thought experiment and an actual one. Make a curves adjustment layer, but set the blending mode to "luminosity". Now, you can't do anything with the curves which will change the colors, only the contrast. So we are only thinking about contrast.

What additional control can you get at this point from using the individual curves over what you will get from just the master curve? Well, you can adjust the contrast of very blue things separately from that of very red or green things. It's very similar to making a good B&W. Once you convert you've lost information which may be useful. Similarly, using just the master curve loses the chance to address the contrast of different colors separately.

I have used this technique frequently and found it quite helpful in certain images, particularly images where you are trying to restore detail and contrast in something in the top or bottom quarter tone. In those cases, you just don't have a chance with a global curve without really messing with the mid-tones more than you want, but you can sometimes do some really nice things with color curves set to luminosity mode. BTW, I learned this technique in Dan's LAB book and you can see some examples of it in my chapter 14 writeup (http://www.dgrin.com/showthread.php?t=26724) on separating color from contrast in RGB.

[Al Pomina]

I have used this technique frequently and found it quite helpful in certain images, particularly images where you are trying to restore detail and contrast in something in the top or bottom quarter tone. In those cases, you just don't have a chance with a global curve without really messing with the mid-tones more than you want, but you can sometimes do some really nice things with color curves set to luminosity mode. BTW, I learned this technique in Dan's LAB book and you can see some examples of it in my chapter 14 writeup (http://www.dgrin.com/showthread.php?t=26724) on separating color from contrast in RGB.

After seeing the corrections submitted I decided to send mine. Each channel was adjusted independenly. I used the gray hair on the left for white point and the blurred black coat in the background for the black point. Also put a marker in the face and the shirt. I think that it's better that what have been show so far. How may I send the image to you? I'm new at this :dunno
alpom111@yahoo.com

[Andy]

After seeing the corrections submitted I decided to send mine. Each channel was adjusted independenly. I used the gray hair on the left for white point and the blurred black coat in the background for the black point. Also put a marker in the face and the shirt. I think that it's better that what have been show so far. How may I send the image to you? I'm new at this :dunno
alpom111@yahoo.com
Hi Al,

You can link your images from your website... or you may attach them to a post.
More here: http://dgrin.smugmug.com/gallery/1083138

[Al Pomina]

Hi Al,

You can link your images from your website... or you may attach them to a post.
More here: http://dgrin.smugmug.com/gallery/1083138

Thank you for the info.
Here is one of the images

Al

[rutt]

Straight from the horse's mouth:


For example, think of an image of a red rose, green leaves. In the red
channel, the flower is a highlight, the leaves mid- to three-quartertones. In the
green, the leaves are midtones and the flowers shadows. In the blue, all
interest objects are shadows.

Clearly you can get more contrast by customizing the shape to each channel:
the red has nothing of importance that's very dark, but in the other two the
darkest areas are critical but the light areas, which are critical in the red,
are unimportant.

Such an image has critical detail in *at least one channel* in every range
from lightest to darkest. A master curve adjustment applies the same move to
each channel, guaranteeing that contrast will be damaged in at least one critical
area. With three separate curves there is no such problem.

[Pindy]

Just bought the 5th ed. based on the various recommendations here. Aside from the fact that the first 2 chapters made my brain hurt, I'm starting to wonder how much I should take to heart Dan's insistance on never using the main curve instead of the individual channels. I appreciate the superiority of curves to Levels (I use Aperture and I want to make its own Levels work but they are clumsy for all but white/black points imho) but this notion that you're lapsing into dereliction of duty by using the main curve line is a bit of a shock. Clearly the guy is beyond hip, PS-wise and I prostrate myself. Reading his views make me think that neither Aperture nor Lightroom will ever be worthy of your adjustments. This is severe, but that's the line he seems to be towing.

I'd be glad to hear the opinions of the more experienced in this regard (all of you).

Thanks

[DavidTO]

Pindy,

I've come to the conclusion that the cost/benefit of adjusting individual curves rather than the master curve is too high. It's just not worth it, IMO, as it can too easily cause more problems than it's worth, and I am far too lazy and have better things to do than to spend time on the miniscule benefits of this method. A professional retoucher might find it worth pursuing, but for the average joe photographer like you and me, it's just a waste of time, IMO.

[Nikolai]

After finishing and reviewing PPS5 and all the discussions here I started to set the curves (and level) adjustment layers to Luminosity mode, but that's about it.

While I believe there are some images where channel based curve/level adjustment are indeed necessary, for the vast majority of *my* images it's akin to crossing the mine field blindfolded to get a 1% discount on a sandwich. Minuscule benefits with the tons of risk and efforts. ROI is down the drain.

Maybe at some point in the future, when I get somewhat closer to Dan's level... Now I'm glad if my image is not OOF :-) :wink :rofl

Besides, who needs those minute adjustments if you are actually trying to get something like this:

http://nik.smugmug.com/photos/134504881-M.jpg

Cheers!

[Duffy Pratt]

I'm not making adjustments anymore on the RGB master curve. If I'm going to do curves in RGB, its usually to get rid of a cast or to balance skin tones. In those cases, individual curves are almost a must.

If I'm going to be curving simply for contrast, I would probably just move to LAB and do the curves there. There is almost always something else that is better done in LAB anyways (color contrast, shadow/highlights, L channel sharpening).

Duffy

[rutt]

I talked about this with Dan only yesterday. I think the first few chapters of PP5E are really confusing compared to the LAB book. The technique of using separate RGB (or CMYK) curves for contrast is an advanced technique IMHO. It has its place in the arsenal of someone who deals with a lot of images and has very high standards for the results but it wouldn't be the first thing I taught.

The first thing I would teach is the Ch 1. technique from the LAB book. And, in fact this has proven to be a very successful way to get people going. Blending in RGB for contrast is the next thing I'd teach, perhaps by teaching B&W conversions. Somewhere in there I'd work on sharpening.

The real value added in PP5E IMHO is in the later chapters, starting with Ch 15. These are really advanced techniques, but they can make a huge difference for some images, particularly when there are brightly colored objects, for examples flowers. False images are also really worth understanding. They can be the very fastest way to correct over/under exposed images not shot in raw.

I've been thinking that if I were Dan I'd try to unify the two books to get the great on-ramp of the LAB book and the best of the advanced techniques from PP. If anything, I'd split the content aimed at commercial printing into a separate book or section.


Anyway, I'd like to get things moving. I believe we have takers for both chapters 9 and 10. Do you know who you are? If not, I'll try to dig you up from my email and PMs. After that, let's split to chapter 15. Perhaps I'll take that one unless someone else wants it. After that, we should collect some brightly colored flower shots (maybe with faces) also wild colored clothing. Chapters 16-19 should help get a drammatic improvement in these.

[Nikolai]

John,
maybe you or somebody else advanced enough can do the rest of us mere mortals a small favor and show on a sample image how to use channel based curves (yet again) and explain why this curve, why at this particular points, etc.
The only limitation - the image cannot be yours, or Dan's, since I want to see how it works in the real, imperfect, world:-)
I'm willing to provide such an image...

[dandill]

...and explain why this curve, why at this particular points, etc. This week I have been attending Dan Margulis's sessions at Photoshop World Boston.

I learned that he selects regions of the R, G, and B curves by running the eye dropper over the "relevant" part of the image, and then adjusts the curve in just the part spanned by this sampling. That is, he doesn't set points; rather, he just eye-balls the region where the sampling falls on each curve and then adjusts the curve in just that region. It is very quick (a few seconds for each curve) and in each case very effectivive. The simplicity was a revelation; I had completely missed it reading the books

I hope this helps.

[Nikolai]

...The simplicity was a revelation; I had completely missed it reading the books
...

Do you think you will be willing to reproduce this simplicity for the rest of us? :bow

[dandill]

Do you think you will be willing to reproduce this simplicity for the rest of us? :bowFair question! Do you want to post an image for us to fiddle with?

[Nikolai]

Fair question! Do you want to post an image us to fiddle with?

Thank you! :thumb I will tonight... :deal

[Pindy]

thank heavens!

[Nikolai]

Fair question! Do you want to post an image for us to fiddle with?

Done.
http://www.dgrin.com/showthread.php?t=58191
TIA! :thumb

[rutt]

I know, Nik, that you want me to play with your image. I'm going to do that, but, sorry, I'm not going to promise to improve it. The reason is that I don't think the channel-based curve technique is the best technique for every image. In fact, as I keep saying, I think that Dan made a kind of mistake by introducing it before blending a basic technique for improving contrast for different elements of an image independently based on their colors.

Nevertheless channel based curves have their place. So first let's agree about what exactly we are talking about. Dan contends that:

Using separate curves on a luminosity blended curves layer gives better control over different areas of the image in some cases. Note that because the curves are luminosity blended, this is a contrast move, not a color move.
Using separate curves on a color blended curves layer gives better control over color.

2 should be uncontroversial. It's the first step of the portrait recipe and I use it all the time to correct the yellow-magenta balance in flesh. I hope you do that, too. If not, I'm glad to supply some examples.

So we are really talking about how effective 1. is. Before we start with it, let's remember an important fact: Photoshop's luminosity formula:

.3R + .6G + .1B

Why is this relevent here? It means that changes to the green channel curve have 6x more impact on the luminosity of the image than changes to the blude curve and 2x more impact than the red curve. This imbalance is the reason I think this technique is difficult to use and should be taught as a secondary technique to channel blending (chapters 6 (http://dgrin.com/showthread.php?t=52724) and 7 (http://dgrin.com/showthread.php?t=53842).)

Nevertheless, let's see what channel based curves can do in RGB. I'll start by opening up the image with a false profile, same as Duffy did. I'm doing this to open up the shadows and to give the curves more room to work. Here is the image after I assigned it to a 1.0 gamma sRGB profile and then converted it back to real sRGB:

http://rutt.smugmug.com/photos/141746183-L.jpg

Washed out, but except for the sky, a better starting point for our pedagogical purposes than the original. If I were illustrating blending instead of curves, at this point the first thing I'd do is use the red channel as a luminosity blend for the sky to recover some more detail there, or better in this case, keep the original before the false profile and use that for the sky. In fact, I think I'll do just that:

http://rutt.smugmug.com/photos/141748578-L.jpg

With this starting point, I wrote a composite curve to try to reestablish a good dark point, get some depth in the faces and get better contrast in that flag and sky. (Remember I'm using a luminosity blended curves layer here.)

http://rutt.smugmug.com/photos/141751709-S.gif

http://rutt.smugmug.com/photos/141752466-L.jpg

Can we improve on this by using the separate channel curves? Yes.

http://rutt.smugmug.com/photos/141753687-S.gifhttp://rutt.smugmug.com/photos/141753696-S.gif

http://rutt.smugmug.com/photos/141753706-L.jpg

(Again, remember this is a luminosity blended curves layer.)

Why is this better? Because I was able to keep better shadow detail while establishing a dark point. I was able to do this by making the dark end of the red (the weak channel for the soldiers' pants) steep. I got better depth in the faces, sky, and reds of the flag by making the green channel steeper in the highlights and midtones where these things live. What about the blue channel? Forget it. It's only 10% of the luminosity calculation, so it doesn't do much and I ignored it.

Is this the best I can do with this image? No. It's meant only as an illustration of what can be done with RGB channel based curves vs the composite curve.

Maybe I'll redo this image using all the tools and see how I can do. But that isn't the point is it? You wanted to know what channel based curves were good for and I have tried to illustrate.

[Duffy Pratt]

Rutt:

When you do the "once for color/once for contrast" approach to curves, the point seems pretty obvious. The more ways that you can segregate contrast before curving, the finer control you can have. By the same token, thats why curving in CMYK gives even more control. Instead of three areas to work with, you have four, and as a bonus, one of those areas is a natural selection of shadows.

Dan, however, shows curving the separate channels in a Normal blend. This is a much trickier thing to do. I've been practicing it quite a bit over the past few months, and am still surprised (sometimes unpleasantly) by the results. I think the resistance to PP5's approach in the early chapters comes from the union of color and contrast in these curves.

The main trouble I have with the "once for color/once for contrast" approach is that a big change in contrast does change the color. In LAB terms, brown and red are the same thing. But the commonsense approach says that they are different colors. That said, more and more I'm coming around to seeing the usefulness of the two step approach to color and contrast.

Duffy

(Edit: I suppose I should have called it "once for contrast/once for color". Because color changes when you change contrast, it makes sense to me that you should get your contrast the way you want, or close, before doing the fine color correction.)

[rutt]

Duffy, I've also been thinking about the reaction to those early chapters, especially in comparison to the success of the LAB book. I've even talked to Dan about it. Of course, these days, he's experimenting with something totally different: false profile to decrease gamma a lot, convert to CMYK. Steepen K, keep copy of K channel somewhere, convert to LAB. Steepen A+B through a layer mask containing that saved K channel, HIRALOAM all three channels. Of course, his results look great, mine, not so much yet. Dan demoed this at MIT on Wednesday.

In the last advanced class I took, Dan really stressed luminosity blending for contrast enhancement. I'm just beginning to get my mind around this.

If I were Dan (or his editor), I'd unify PP and the LAB book. I'd start with the first four chapters of the LAB book. I'd do impossible colors, including RGB channel curves for color. I'd teach blending. I'd teach sharpening including HIRALOAM and how to blend HIRALOAM and USM. Only then would I get into RGB channel curves for contrast.

But then who am I? I can't reproduce Dan's results even after they have been clearly demonstrated any number of times...

[Nikolai]

Thank you so much for your time! :bow

This is exactly was I was looking for :-) :clap

Now, to the things I got (and not... :rolleyes )


Curves in luminosity blend.
Heck, I didn't get that from Dan's book. However, as I indicated in the other thread, I have recently started to use curves (and levels) in Luminosity mode almost exclusively and even it was only a master curve, I was quite satisfied with this approach. Now, after reading your post, I feel kinda stupid, since in L-mode I could go to individual channels and get finer controls of some colors, yet still not screwing up a whole lot... So, if nothing else (which is not the case), your post was a great help/revelation! :thumb
Separate steps for contrast/color.
Again, great approach, makes total sense. It is much easier to control this beast this way! :thumb
Chanel curves in normal mode for the color shift fix.
Since I shoot RAW, it's not an issue. Pretty much all my portrait work was done in the controlled light environment, which means one shot with the gray card, one click in ACR - and whatever color cast was present is gone for good. I do understand it's possible to do via channels, but to me it would be a huge overcomplification.
Thing I didn't get from the book and I'm still not getting - false profile.:dunno Why is it a better starting point? How one decides on which gamma value to choose? Why not use middle Levels slider in PS or Exposure in ACR, which are, to a degree, doing the same thing, and are far easier to control? :scratch
It would be great if you can elaborate on this...Once again, I do appreciate your sharing! :lust

[rutt]

[Chanel curves in normal mode for the color shift fix.
Since I shoot RAW, it's not an issue. Pretty much all my portrait work was done in the controlled light environment, which means one shot with the gray card, one click in ACR - and whatever color cast was present is gone for good. I do understand it's possible to do via channels, but to me it would be a huge overcomplification.

I shot this in raw under mixed light (window, florescent). I tried various things in ACR, but there was no escaping that mixed cast. In the end I converted with AUTO white balance:

http://rutt.smugmug.com/photos/141877129-L.jpg

See how the window light makes a blue cast in the highlights (and the artificial light makes a yellow cast in the darker parts of his face?

Easily fixed with one blue curve:

http://rutt.smugmug.com/photos/141877361-S.gif

http://rutt.smugmug.com/photos/141877168-L.jpg

I just command-clicked on the parts of the image I didn't want to change, then command clicked on the part with the blue cast and moved that point toward darkness, to get the blue out of the highlights without changing anything else. Because this is the blue curve, it doesn't have much effect on contrast, but I could have set the blending mode of the curve layer to "color" if I were being paranoid.

This move is a prelude to the rest of the workflow. It's a first order color balance correction that targets more narrowly than color balance in ACR or a LAB curve correction. Sometimes a blend can do better, but this is my workhorse correction for mixed cast portraits (including ballet under theater lights.)

Thing I didn't get from the book and I'm still not getting - false profile.:dunno Why is it a better starting point? How one decides on which gamma value to choose? Why not use middle Levels slider in PS or Exposure in ACR, which are, to a degree, doing the same thing, and are far easier to control?

I'm also just getting the hang of false profiles. It takes some setup, but I've watched Dan do amazing things with it over and over. It's like having a huge curve library at your command. Dan likes to tell the story of a photojournalist who uses only false profiles as a post processing technique. But it's a very powerful way to make the entire image lighter, darker, more colorful, etc with a single move. In the case of your civil war image, it really opens up the shadows, a good preparation for curves, blending, etc. But as I said, I'm still getting the hang of this. Hope the reading group gets to it.

[Nikolai]

I shot this in raw under mixed light (window, florescent).

I see... Makes sense.
Also this whole "locking the parts you don't want to change" idea became MUCH clearer after you guys started to do your magic in this thread. :deal :thumb :clap

As to the false profiling... I guess you must have this library and this amount experience first to be able to use it effectively. I also need to re-read the book about how it's done, since during the first read it was way over my head...:dunno

[bas]

Practicing with rgb curves

http://img292.imageshack.us/img292/6710/119679475oflu8.jpg

http://img376.imageshack.us/img376/4920/curvesrd6.jpg

[jjbong]

I'm new to the forum. I've been reading the posts on this thread and seen
much discussion/question about the benefits of using curves in separate
channels vs. composite curves. I think a recent post demonstrated the former
reasonably well.

The only thing I'd add, based on my own experience (including taking one
of Dan's classes) is that this seems to be especially effective in CMYK,
and much trickier in RBG. I don't completely understand the science behind
it, but it seems that you can make bigger moves in CMYK curves that bring
out the details (read contrast) without screwing up the colors noticeably.
I can post a picture or two if anyone's interested.

I'm an RGB guy. The first day of Dan's class, we had to do everything in
CMYK. Based on that, I now do almost all of my curving in CMYK, and I'm
very happy with the results. Occasionally, I'll try it in RGB. Depending on
the picture, it can work well. But mostly, I find it easier (and quicker) to
do in CMYK.

The black point/white point setting is entirely by the numbers. Contrast
setting is done by moving the cursor over the interesting part of the
picture, and seeing where it lands on the curve (an earlier post discussed
this - I also didn't get this from the book, but saw Dan doing it in person).


John

[rutt]

The only thing I'd add, based on my own experience (including taking one
of Dan's classes) is that this seems to be especially effective in CMYK,
and much trickier in RBG. I don't completely understand the science behind
it, but it seems that you can make bigger moves in CMYK curves that bring
out the details (read contrast) without screwing up the colors noticeably.
I can post a picture or two if anyone's interested.

I'm an RGB guy. The first day of Dan's class, we had to do ever

Please do. Thanks.

[pathfinder]

The ease of writing curves for contrast without altering colors in CMYK makes sense. There are four channels, not three.

The individual color curves have lesser effect due to the addition of the black channel where much of the contrast and shadow detail lie. This is why curves in CMYK can be easier, if your brain is used to thinking in CMYK as pre press color editors are used to.

Unfortunately, my brain tends to work in RGB for some reason, hence writing CMYK feels like drawing with my non-dominant hand:scratch

[Nikolai]

With all due respect, I don't believe that any given single color space is a panacea. Different images and different tasks require different treatments, different tools and different spaces. Mastering one space is good, but why stop there? :rolleyes

[rutt]

Unfortunately, my brain tends to work in RGB for some reason, hence writing CMYK feels like drawing with my non-dominant hand:scratch

Just keep saying to yourself "CMYK is RGB". C = R, M = G, Y = B. More cyan is less red, more magenta is less green, more yellow is more blue.

Make a new blank document in Photoshop. Try RGB curves. Move the light endpoint of the red curve toward darkness. What happens? Less red and the image becomes cyan. Why? Because green and blue light is what's left.

Now cancel your curve and convert that plain white document to CMYK. Get a curves dialog and pull the light end of the cyan curve toward darkness. What happens? It become cyan, not surprisingly. You've added cyan ink, making the image darker. But how? By adding the ink that reflects green and blue but not red.

But you knew that. Mostly the very same curves translated from RGB to CMYK with R=C, G=M, B=Y will do the same thing. Except in the shadows. And where the shadows start is a function of the definition you use of CMYK. See PP5E, ch 5. So use CMYK when you are trying to conquer the shadows or when you are preparing for a CMYK press.

So what's hard about CMYK?

[Nikolai]

So what's hard about CMYK?
I guess it's hard for people who lack the knowledge/experience of the abstract topologies/ "spaces". For me personally all these colorspace shenanigans fade compared to an extremely simple, nice, easy to use and oh-so-forgiving L(2,oo) :wink

[jjbong]

So what's hard about CMYK?

The hardest thing for me coming from RGB was understanding neutrals.
R=G=B is pretty straightforward, but CMYK isn't at first. It turns out
not to be that big a thing, but it was an incredible mental block for me.
Getting past that was quite rewarding, allowing me to solve
problems I couldn't in RGB (bringing detail out in shadows, as you
mention, but also in highlights with custom conversions).

Another practical issue is setting up the curves plot to be consistent
in both spaces (and understanding that less is more, so to speak -
more C ink is less R glow).

In retrospect, I'm amazed that it seemed so hard at first.

[rutt]

The hardest thing for me coming from RGB was understanding neutrals.
These days I almost always curve twice, once for color and once for contrast, setting the blending mode of the curves layer with color and [/i]luminosity[/i]. Or I blend for contrast and curve for color. Or I work on casts in RGB and then go to CMYK for work on the shadows with the K curve. I fuss with the "cycan" curve for flesh after LAB corrections by using the red curve in RGB; only when there is some reason this won't work do I do it in CMYK. In any case, I try to avoid needing to neutralize in CMYK.


Another practical issue is setting up the curves plot to be consistent
in both spaces (and understanding that less is more, so to speak -
more C ink is less R glow).
One of Dan's best innovations, little appreciated, but very important for seamless 10-channel work.

[MichaelBorger]

I just came across this thread and am trying to go through Dan's book (2002 PS7 version but I'm sure the concepts are just about the same). Ok, I'm only in chapter 2 but I don't know where he is coming from with some of the stuff he says. I often feel like he's talking down to me. It would help if he would take just a bit more space to explain the rationale behind some of the decisions and assumptions he makes.

I'm not a complete newbie but am entirely self-taught from my camera through PS and have plenty of gaps to fill in. But I'm not sure this book is where I should first be going to do this. Perhaps something more of a 'Post processing finishing school 101' course would be better before I decide (if I decide) to get into Dan's ideas.

[pathfinder]

Michael,

Professional Photoshop 5th Edition by D Margullis is a challenging book. I don't think any of us who participated in that book review would say it was all easy sailing. But it is a very worthwhile journey, that many of us felt the need to take.

I found that I had to work through each example - Kind of like a math textbook:D Only very few folks can just read their calculus textbook, and say "oh yeah, that was obvious".

If this is your first endeavor into Photoshop self education be prepared to be challenged along the way. There are simpler, more direct texts around - Scott Kelby writes a number of good ones. Many of us had already read them, and wanted a deeper understanding of what was happening when we edit an image.

Dan did not title his book PROFESSIONAL Photoshop for no reason. It is addressed to pre press professional and would be serious photographers. It is not a tome for folks without a serious desire to learn. Dan also assumes a more than average understanding of Photoshop usage as well.

If you have specific questions feel free to drop in here and we'll see if some one can't round up an answer for you. It will be good review for those of us who reviewed chapters in this book.

[Nikolai]

I just came across this thread and am trying to go through Dan's book (2002 PS7 version but I'm sure the concepts are just about the same).
While what Jim (Pathfinder) said above is very true, I sincerely recommend to cough out some $$ (it's New Year!) and get 5th edition (you got 4th), as well as his LAB book. Yes, concepts are the same, but he himself changed alot over the course of time. You will find his latest books no less challenging, but more adequate for the digital age... I still own and hold dear a copy of 4th edition (as wel as the other two), but if I had to choose, I'd start with the 5th... Or maybe with LAB - it's kinda easier...
Just my 0.0000002 of the f/stop.

[pathfinder]

Thanks Nik, I missed that he did not have he current edition.

I agree, the 5th edition is really much more relevant for the digital photographer today. I suspect even the author would agree.

[MichaelBorger]

Thanks for the encouragement, guys. I've ordered the Kelby CS2 book and will let that fill in any gaps before proceeding with Dan's books. I don't mind taking extra time to make sure my foundation is solid. I'm sure I'll be redoing many of the photos on my site!