Is there a science to perspective cropping...

[rutt]

... or is it a black art? I have a shot that I sort of like:

http://rutt.smugmug.com/photos/19002844-L.jpg

It suffers from whatever it calls when you have to point the camera up to get the tops things into the frame. I played around with perspective crops, but I couldn't tell when I had it right. Is there a way to know? If not, how do you decide?

[cletus]

Have you tried using the free transform tool to get rid of the "lean"? Sometimes I find the preview it provides helpful in making perspective adjustments.

[Andy]

... or is it a black art? I have a shot that I sort of like:



It suffers from whatever it calls when you have to point the camera up to get the tops things into the frame. I played around with perspective crops, but I couldn't tell when I had it right. Is there a way to know? If not, how do you decide?

turn your gridlines on. set the grid to be wide enough that you get some of the lines of the grid on lines in your shot. then use edit>distort, and go gently into these waters. if you don't go crazy, i find it fairly easy to get acceptable results :thumb

[Kirwin]

Hi rutt,

I see very little distortion in this image. I simply used a straighten picture tool and achieved acceptable results. I hope this helps.

[rutt]

turn your gridlines on. set the grid to be wide enough that you get some of the lines of the grid on lines in your shot. then use edit>distort, and go gently into these waters. if you don't go crazy, i find it fairly easy to get acceptable results :thumb

This chimney actually tapers to the top, which makes this a little hard.

[devbobo]

This chimney actually tapers to the top, which makes this a little hard.
I generally try to use the verticals in windows, door, walls, etc to square up the image. In this image the bridge uprights and the building provide a good reference.

With this photo, you might want to try rotating slight counter-clockwise to level the bridge and the roof-line first.

Cheers,

David

[Kirwin]

Here is the image after useing the straightening tool...
What do you think?

http://timebandit.smugmug.com/photos/19029101-L.jpg

[devbobo]

Here is the image after useing the straightening tool...
What do you think?


Looks good, but i think it needs to be rotated about -0.9 to level the roof and bridge.

David

[rutt]

Well, I fooled around with it ala Andy and Eric, and then fooled around with it ala me and I got this:

http://rutt.smugmug.com/photos/19031817-L.jpg

Now I'm back to my original point. Is this better? How can I tell? Do I just have to go by feel?

[DavidTO]

To my eye it's more about the barrel distortion.

You could demo LensFix (http://www.kekus.com/plugin/), if you don't already own it.

[John Mueller]

To my eye it's more about the barrel distortion.

You could demo LensFix (http://www.kekus.com/plugin/), if you don't already own it.
Or here is another (http://www.dlynnwaldron.com/ImageAlignPro.html)

[digismile]

If you're not in a hurry, Photoshop CS2 has a pretty cool new filter specifically for addressing lens distortion. It can address Barrel or Pin Cushion distortion, adjust Chromatic Aberration, as well as make adjustments to verticle or horizontal perspective.

Regards,
Brad

[adrian_k]

It probably won't get any harder than a tapering chimney.

That version looks good to me.

Use guides (ctrl+') and there seems to be a "vein" which is probably a lightening conductor that you can use as a vertical.

Well, I fooled around with it ala Andy and Eric, and then fooled around with it ala me and I got this:

http://rutt.smugmug.com/photos/19031817-L.jpg

Now I'm back to my original point. Is this better? How can I tell? Do I just have to go by feel?

[rutt]

It seems that the real answer to my original question is: "No, there is no science, you have to do it by eye."

[XO-Studios]

It seems that the real answer to my original question is: "No, there is no science, you have to do it by eye."
Also, and this might have already been pointed out, pull in a bunch of guides from the side to aide your transformation.

My approach would be

Pull in horizontal guide for the bridge

Pull in three vertical guides, on center tower, and one on each side symmetrical.

Now it is still a 'feel' issue, but at least the guides will tell you where you are, and where you are going.

I personally like guides better than grid, as I can place them exactly where I want them.

(bonus tip guides can be moved by using move tool (V) outside of picture area.)

XO,

[rutt]

Pull in horizontal guide for the bridge


The bridge isn't parallel to the focal plane. The left side is closer to the camera than the left, so I think it shouldn't be level. It is slightly above the level of the camera so I think the right side should be a little higher. Right?

[XO-Studios]

The bridge isn't parallel to the focal plane. The left side is closer to the camera than the left, so I think it shouldn't be level. It is slightly above the level of the camera so I think the right side should be a little higher. Right?
yes, and the guide will guide you in that, i.e. it is just helping keeping the perspective as it should be as you skew and transfrom the picture. You could even pull in a second horizontal guide, one for each side to maintain the original angle.

BTW, I had an a novel thought on this specific picture, pending if the resolution of the original picture is high enough. (3 actually)

#1 If the resolution is high enough, look at individual bricks (or multiples of them) in the tower and use the measuring tool (behind the eyedropper).The perspective is corrected properly when a row of 5 bricks is the same width in pixels in the bottom and in the top of the tower.

#2 Depending on the angle the camera was shooting at, verticals will look like a fan (hence the leaning tower) by measuring the angle of lean, and doing an estimate on the distance you were from the tower (EXIF/META data migh thelp), and the towers position relative to the center of the frame (axis of the lens) help) you could theoretically calculate the angle your camera pointing upwards. using that angle, you can the calculate the relative distance between you and the top of the tower vs you and the bottom of the tower, using that distance as a ration to do your perspective correction. My mind is in no shpae to do the calculation right here right now, but I know it is doable.

#3 Cheater solution. If you are in the field taking a picture like this, next time take a second picture, camera level with horizon, portrait/vertical and snap the tower with the camera level. Use that shot as a reference of tower ratio's and match those ratios in your other shot.

FWIW,

XO,

[rutt]

The originals are there. It was 8MP. Might have enough res.

This is the kind of insight I was looking for.

[philspace]

Thanks for starting the thread Rutt!

I just got my EFS 10-22 and had a couple shots that were good, but needed to be cleaned up - thanks to this thread, corners are straight and it's better than anything I could have ever stitched together :thumb

[colourbox]

It appears that the new Lens Correction (http://graphicssoft.about.com/od/photoshop/ss/cs2morenew_2.htm) in Photoshop CS2 will make these chores much easier.

[philspace]

Thanks, I was thinking about picking up an addon routine or plug-in to deal with it, but maybe I should just wait and make the jump to CS2:thumb