Does anyone know how to

[Sam]

Reduce the noise in this type,(star trail) image?

This is a friends image, and he wants to print it, but doesn't like the noise. I did a test print, and I didn't think the noise was too distracting, but he is particular. Any suggestions will be appreciated.

Sam

Edit: OK I just posted this and the noise is ahrd to se in this small image.

[pathfinder]

Sam, I would select the lower quarter tones with Select >Color Range, mask out the bottom of the image outside the sky, and run the selected area through Noiseware or one of the other noise removal programs. The remaining black sky will be as smooth as a baby's bottom:thumb

[Sam]

Pathfinder,

Thanks for your response. I tried to understand your instruction, but I must admit I don't know how to chose the lower quarter tones?

Also I may have used the incorrect term to describe what the photographer wants to clean up.

Here is a crop of the sky, which hopefully shows what I am trying describe. Maybe a better term would be hot pixels? The points of light between the star trails.

Sam

[pathfinder]

To select the points, and not the trails, is more difficult. You may have to clone them out or use the healing brush on them.

Select > Color Range > Shadow will select the lower quarter tones .

[ziggy53]

Sam,

It looks like your friend did not use the long exposure noise reduction.

They might try to build a "dark frame" exposure, if they remember the original exposure length. They would find conditions similar to those when the original shot was exposed, at least a similar ambient temperature, and expose the camera with a lens capped the same duration as the original image. Then use the "dark frame subtraction" method here:

http://www.takegreatpictures.com/default.aspx?path=/HOME/Columns/Digital_Photography/Details&params=object/9503/_design_/print

Normally, you would do this right after the original exposure so this may not remove all of the hot pixels, but it should find the most persistent pixels and help quite a bit.

Next time, tell them to turn the long exposure noise reduction "on" to produce the best results.

[TrulyAlaskan]

Sam,

It looks like your friend did not use the long exposure noise reduction.

They might try to build a "dark frame" exposure, if they remember the original exposure length. They would find conditions similar to those when the original shot was exposed, at least a similar ambient temperature, and expose the camera with a lens capped the same duration as the original image. Then use the "dark frame subtraction" method here:

http://www.takegreatpictures.com/default.aspx?path=/HOME/Columns/Digital_Photography/Details&params=object/9503/_design_/print

Normally, you would do this right after the original exposure so this may not remove all of the hot pixels, but it should find the most persistent pixels and help quite a bit.

Next time, tell them to turn the long exposure noise reduction "on" to produce the best results.

Yeah, turn on the Long Exposure Noise Reduction. I do quite a bit of night photography and there are 4 major tools needed to make the shots look right: Long Exposure Noise Reduction, Neat Image (or noise ninja,) Hot Pixel Eliminator, and Photoshop.

[Sam]

Thanks everybody! Looks like a little reading in in order,

Sam

[Nikolai]

Sam, for the image like this there is a relatively simple approach that would clear most of the image, specifically the most of the sky.

Create a new duplicate layer (Ctrl+J)
Change its blending mode to Darken (or Darker - you can play with either later)
Select the whole layer (Ctrl+A)
Activate free transform tool (Ctrl+T)
Position the middle (pivot) point precisely(!) at the rotation center. It should be a few minutes off Polaris
Rotate the layer just a tad. You will lose the end points of the star trails and most (if not all) of the noise dusticles.
If you mispositioned the pivot point, press ESC to abort the transformation, reposition the pivot point and repeat steps 5-6
Once you satisfied with the results, hit Enter to confirm the transform
Add mask and brush out the landscape part and whatever artifacts you may have gotten alone this way
That's all folks! :wink

The idea here is that rotation would keep the arcs within themselves, thus leaving them pretty much intact.
At the same time, the brighter noise particles would be moved against the mostly black sky and the blending mode will kill them immediately.

[TrulyAlaskan]

Sam, for the image like this there is a relatively simple approach that would clear msot of the image, specifically the most of the sky.
Create a new dulicate layer (Ctrl+J)
Change its blending mode to Darken (or Darker - you can play with either later)
Select the whole layer (Ctrl+A)
Activate free transform tool (Ctrl+T)
Position the middle (pivot) point precisely(!) at the rotation center. It should be a few minutes off Polaris
Rotate the layer just a tad. You will lose the end points of the star trails and most (if not all) of the noise dusticles.
If you mispositioned the pivot point, press Esc to abort the transformation, reposition the pivot point and repeat steps 5-6
Once you satisfied with the results, hit Enter to confirm the transform
Add mask and brush out the lanscape part and whatever artefacts you may have gotten alone this way
That's all folks! :wink
The idea here is that rotation would keep the arcs within themselves, thus leaving them pretty much intact.
At the same time, the brighter noise particles would be moved against the mostly black sky and the blending mode will kill them immediately.

You sir deserve a beer!! This saved me about 4 hours of work! You are THE MAN!
:beer

[Nikolai]

You sir deserve a beer!! This saved me about 4 hours of work! You are THE MAN!
:beer

You're welcome :-) :thumb

Can we see the results? :wink

[TrulyAlaskan]

Sure thing, as soon as I'm done with all of them lol. You just opened my eyes to a new way to edit these!

[Nikolai]

Sure thing, as soon as I'm done with all of them lol. You just opened my eyes to a new way to edit these!
Glad to be of help:-) :D

[pyry]

The idea here is that rotation would keep the arcs within themselves, thus leaving them pretty much intact.
At the same time, the brighter noise particles would be moved against the mostly black sky and the blending mode will kill them immediately.

I see that could be used to bridge gaps in the trails if you've shot them as a bunch of shorter exposures.

Nik, you're a genius!

[Nikolai]

I see that could be used to bridge gaps in the trails if you've shot them as a bunch of shorter exposures.

Nik, you're a genius!

That's could be done, too:-) Thanks! :thumb

[Sam]

Nikolai,

Thanks for taking your time to post this!!!!

Sam

[Nikolai]

Nikolai,

Thanks for taking your time to post this!!!!

Sam
Sam, you're welcome, I hope you can use this method to clean up that very nice image of yours...:thumb