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Photo Retouching "Improving" photos, post-production, correction, etc.

color noise

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  #1  
Old 10-23-2007, 02:53 PM
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jenniferfrances jenniferfrances is offline
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color noise

Hello all!
I did a quick search in the forums for techniques used to eliminate color noise in shadows.
I am aware of the reduce noise filter but it seems to give that gaussian blur effect.
Another have any other methods?
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Old 10-23-2007, 03:33 PM
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Re: color noise

Check the channels often noise can be more pronounced in one of the channels and then you can look at reducing the noise there. you can also try to color correct the color in the shadows to make it blend better with the shadow.
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Old 10-23-2007, 04:17 PM
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Re: color noise

Jennifer, that type of noise is quite common in underexposed areas of digital images. I have found the mosteffective way to reduce or eliminate the noise without over blurring the image is a good noise reduction plugin like Noiseware, Neat Image , or Noise Ninja. I find Noiseware the best of the 3.
Regards, Murray
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Old 10-23-2007, 05:30 PM
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Re: color noise

Easiest way (in Photoshop):

1) Duplicate layer
2) Change blend mode to "Color"
3) Gaussian blur (1-2 pixels is usually enough)
4) Merge

Use a luminosity mask or Select -> Color Range to perform step (1) on just the shadow areas if you like.
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Old 10-23-2007, 05:34 PM
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Re: color noise

im not necessarily looking for the easiest way
but i will definately give this a whirl..
thanks a bunch
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Old 10-23-2007, 05:39 PM
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Re: color noise

Quote:
Originally Posted by creeduk View Post
Check the channels often noise can be more pronounced in one of the channels and then you can look at reducing the noise there. you can also try to color correct the color in the shadows to make it blend better with the shadow.
how do i reduce the noise in individual channels?
dup channel then blur or reduce noise filter?

and thanks for your help
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  #7  
Old 10-24-2007, 09:05 AM
edgework edgework is offline
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Re: color noise

Convert to Lab.

Blur the a and b channels.

Convert back to RGB and place on top of your original.

If your shadow areas are pronounced, you can probably blend using Blend-if sliders to smooth the transition into the shadow range. Otherwise, mask and paint back to taste.
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Old 10-24-2007, 09:35 AM
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Re: color noise

edgework gave one the most used methods, using LAB.

TO do it in RGB you can simply move to the channels tab, select the desired channel, and the Noise reduction filter is still available and will function on that channel alone.

Or under the Noise Reduction panel, select advanced and you will now see a new tab "Per Channel" this area allows you to address the channels separately.
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  #9  
Old 10-24-2007, 12:08 PM
seedomo seedomo is offline
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Re: color noise

Edgework certain gave the best example but I would add a very important step. You will want to blur the A and B with surface blur or use dust and scratches to preserve the color detail of objects that have sharp edges. To visualize the technique, since a and b are usually hard to see, you can add a crazy adjustment curve layer set to color blending mode over the BG layer to increase the contrast of the two channels while you play with the blur filters. Another way, often overlooked in photoshop, is to first select the two channels using shift-click. THEN, press the ~ key which will show you the whole image while you are only working on the two color channels you have selected. I was just working on a painting that had subtle details of color and it was the first image I couldn't successfully work on in Neat Image (IMHO, the very best of all the noise programs) LAB is certainly the ONLY way you should approach this since color blending in RGB is VERY bad. This is a very difficult thing to explain, but better shown by a test.
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File Type: jpg colorblur.jpg (72.9 KB, 24 views)
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  #10  
Old 10-24-2007, 12:27 PM
seedomo seedomo is offline
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Re: color noise

After posting the previous test, I concluded that this was an unfair and inaccurate presentation of the difference. The previous test was taken right from Photoshop Lab Color: The Canyon Conundrum: And Other Adventures in The Most Powerful Colorspace
By DAN MARGULIS
I think Dan's examples are unfair since the top right image (Lab version) didn't show the L channel which made it look so much better than the RGB (set to color mode) that was the bottom right image. I have made my own examples that show both Lab and RGB without any luminance detail change. Notice how RGB brightens some of the colors and darkens others. The lab, on the other hand, is able to blur them without brightening or darkening any of them.
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File Type: jpg truetest.jpg (45.0 KB, 22 views)

Last edited by seedomo; 10-24-2007 at 02:33 PM.
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