Photoshop: Pasting any of the copied RGB channels will contain noise. A bug or some conversion / color mode problem?

  • 1
  • Problem
  • Updated 2 years ago
  • Solved
  • (Edited)
In short, copy / pasting a grayscale image from any of the RGB channels into photoshop layers will contain noise. Any idea why this happens and how to avoid it?
  1. New RGB Color image.
  2. Fill the image with any gray value, in e.g. 128,128,128.
  3. Go to the channels panel and select any of the single channels, in e.g. Red.
  4. Select all and copy to clipboard.
  5. Click all RGB channels back to visible and go back to layers panel.
  6. Paste the clipboard content.
  7. Add a levels adjustment layer and squeeze the sliders close to the histogram peak.
  8. Be amazed about the revealed noise.
Photoshop version: 2015.5.0 / 20160603.r88 x64
OS X version: 10.11.5
Photo of Hannu Hoffrén

Hannu Hoffrén

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  • Baffled

Posted 2 years ago

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Photo of Jeffrey Tranberry

Jeffrey Tranberry, Sr. Product Manager, Digital Imaging

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Official Response
From Russell Williams (Photoshop Architect):

"It's as designed. It’s a result of copying a single channel results in a grayscale image. When you paste that into a layer, you’re converting a grayscale image (implicitly whatever your grayscale profile is) to an RGB image (whatever your document profile is), with options as specified in color settings. If you’re using the defaults, that’s converting a grayscale image of “dot gain 20%” to sRGB, with dithering on (which hides banding). The lightness difference (which you can see visibly or with the histogram panel) is because of the gamma difference between the “20%” default grayscale profile and sRGB’s 2.2 gamma. If you switch the grayscale profile to be “gamma 2.2”, the brightness will match. If you turn off the “use dither (8 bpc images)” option, the noise will go away."