Here are my exact steps:
- Open an sRGB or AdobeRGB image in Photoshop
- Convert to a linear(gamma 1.0) RGB color space
- Convert back to sRGB or AdobeRGB
At this point the image looks the same as from the start as expected. At step 2 however shadows look significantly darker. It's not possible use level adjustments with confience as the image with look different by step 3. I repeat the same steps in this GIMP build http://www.partha.com/downloads/Gimp-2.9.3-color-patched-64bit-portable.exe and unlike in Photoshop I have tonal consistency in step 2. What's going on here?
EDIT: The issue is only visible for magnification factors below 67%. To rule out GPU acceleration bugs you should set Preferences>Performance>Graphics Processor Settings>Advanced Settings...>Drawing Mode:Basic
Another issue with a linear gamma working space in PS is setting black levels. The adjustment range is very coarse.
Does anyone in the community use PS and linear working spaces or do you prefer to use other software? Or do stick to gamma encoded working spaces in PS?
Andrew pointed shadow treatment is a long standing problem with Photoshop showing up in various ways.
I only use gamma=1 for measuring absolute light levels. As Andrew pointed out, banding is there for other gammas too but is more noticeable for gamma=1 in dark shadows because vision is more sensitive to fixed light level changes at low luminance than at high. It appears when displaying images the interpolation process runs in 8 bit mode for display purposes. When looking at values in 16(15 actually) bit RGB mode they are sometimes shown as 15 bit values but rounded to 8 bits. At other times they are correctly displayed. At least for me. Isn't clear when they are shown incorrectly but I wouldn't trust any eyedropper readings below 100%. GPU and 30bit color makes no difference in my system. Current Photoshop CC, x64 Win10, CG318.
I found this process shows the effect quite strongly.
1. Create a 2000x1500 rectangle in Adobe RGB space, 16 bit.
2. Use a gradient fill going from 0 to 255
3. Convert to gamma=1 RGB.
At 100% the gradient is quite smooth.
At 50% the gradient shows strong shadow banding.
My system switches out of banding when going from 63% to 64%. This appears slightly different from what others see.