Photoshop - Perceptual colour space conversion not working

[digitaldog]

That is understood by everyone.

Gotta say,  I personally don't know what everyone understands.  

I think what shadowblade is asking for is what would the proper workflow be to achieve a genuine Perceptual conversion to sRGB that really prevents clipping. I.e. what in-between steps to do to convert his Adobe RGB/ProPhoto RGB into sRGB achieving real colour compression for those colours falling out of the sRGB gamut. And I'd like to know about this workflow as well

That's easy, get the sRGB profile that has a perceptual table. I provided a link for one such profile.

[Doug Gray]

What the OP needs is a device link profile that goes perceptually directly from Adobe RGB to sRGB. This would bypass the PCS and should produce the best results since both source and destination gamuts are known. But I haven't run across one.

[digitaldog]

“There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffet 

[Doug Gray]

That's easy, get the sRGB profile that has a perceptual table. I provided a link for one such profile.

Here's how you apply the transformation in Photoshop using your link to the Perceptual sRGB profile at color.org.
http://www.color.org/profiles/srgb_appearance.xalter

0. download and install the profile.
1. Load the image that's in Adobe RGB.
2. select and use the sRGB Appearance profile with Photoshop's Convert Profile selecting Perceptual intent.
3. Assign the standard sRGB profile to the converted image. This prevents undoing the conversion accidentally.

Should prevent abrupt clipping at gamut edges in most cases. Whether one likes the outcome or not one has to live with the smaller sRGB gamut and colors will shift a bit.

[shadowblade]

Found that same profile and gave it a try after I posted this thread.

Either Perceptual intent still doesn't work properly, or parts of the gamut contained in that profile still fall outside sRGB.

I tried it first by creating a colour gradient in Adobe RGB (Red values 10-245 from left to right, Green values 10-245 from top to bottom, Blue at 10 throughout, creating a two-dimensional gradient from 10,10,10 to 245,245,10 in Adobe RGB space). Conversion using the default sRGB profile just clipped large swathes of it, as expected. On conversion to sRGB (Perceptual, using the color.org profile), all the colours shifted, many quite dramatically - as expected with Perceptual conversion - but many parts of the gradient were still clipped at 0 or 255 in one or more channels.

I then tried it with several real photos. The results were better - significantly better than relative colorimetric conversion, given that a lot of my photos are highly saturated - but still clipped in areas.

[Doug Gray]

Found that same profile and gave it a try after I posted this thread.

Either Perceptual intent still doesn't work properly, or parts of the gamut contained in that profile still fall outside sRGB.

I tried it first by creating a colour gradient in Adobe RGB (Red values 10-245 from left to right, Green values 10-245 from top to bottom, Blue at 10 throughout, creating a two-dimensional gradient from 10,10,10 to 245,245,10 in Adobe RGB space). Conversion using the default sRGB profile just clipped large swathes of it, as expected. On conversion to sRGB (Perceptual, using the color.org profile), all the colours shifted, many quite dramatically - as expected with Perceptual conversion - but many parts of the gradient were still clipped at 0 or 255 in one or more channels.

I then tried it with several real photos. The results were better - significantly better than relative colorimetric conversion, given that a lot of my photos are highly saturated - but still clipped in areas.

The sRGB Appearance profile still clips when source colors fall outside the PRMG (Perceptual Reference Media Gamut). There are many colors near the edges (10 and 245) of Adobe RGB that are outside the colors possible from reflective media (with standard illuminants). The profile itself has no idea what the source image gamut is and doesn't know whether it is coming from ProPhoto RGB, Adobe RGB, or any other source. By the time it sees data to map to Perceptual that data is in CIELAB.

The PRMG is supposed to be roughly a gamut bounded by reflective colors found in real life. Lots of Adobe RGB (1998) colors are outside that. Expect that they will clip at gamut boundaries.

Added: Since even some sRGB colors are outside of the PRMG, you can actually see some expansion in some areas though most changes are compression. For instance the green color that is sRGB value (125,250,125) will clip on the green channel when converted through the sRGB Appearance profile.