Why does the Gamut Warning change when I change rendering intent?

Yes. Black point compensation should always be on. In a normal situation there is no reason to ever uncheck it.

Here’s an illustration showing why you want to use BPC, especially when the Intent is Relative Colorimetric. There are 4 samples showing as actual color RGB in the Info panel, and there is significant separation in the Actual values between #1 and  #4:

If I set the samples to Total Ink, I can see #1 thru #3 will output to the same CMYK values:

Turning on BPC creates relative separation between all 4 output values:

The gamut warning difference is coming from your Black Point Compensation setting, which is also showing in the shadow output numbers. I think in general you should always check BPC, otherwise your shadows will fill in on press—with it unchecked there is less separation between the black point and shadow numbers on the conversion:

Hi

its not possible for me to answer this with complete authority, because what happens inside Photoshop's programming isn't known to we forum volunteers.

However, my friend Steve Upton of Chromix, [software engineer & developer of the excellent ICC profile "Swiss army knife" toolbox: Colorthink and Colorthink Pro] has a take on this that makes sense. Here is my understanding of our talk.

Colorthink SW has a gamut warning option http://www.colorwiki.com/wiki/Quantify_Out_Of_Gamut_Colors and that can show out of gamut areas differently to Photoshop's [it also has a sliding scale]. Steve explained why they differ, in his opinion, as I understood it - what Adobe are showing you in Photoshop is which pixels will be remapped [during the conversion] by an amount that exceeds a certain threshold.

So, that’s apparently not, strictly speaking, showing you just what is outside the destination gamut boundary, rather revealing which pixels may be compromised by extensive remapping. Its useful, of course, and does the job, but Steve thinks it's not quite doing what most users think it is. 

here's a discussion on gamut warning: https://lists.apple.com/archives/colorsync-users/2008/Feb/msg00200.html

The Relative Colorimetric and Perceptual rendering intents deal with the mapping of out of gamut colour differently (you know that, right) and that's probably why you may see a difference in the "gamut warning" in some images and with some colour spaces.

That, or one of the profiles is broken somehow, or poorly crafted!

In a quick test I could not reproduce what you are seeing - 

Please attach your test image [or upload to wetransfer and post a link] with the document profile embedded, of course and also let us know the profile you're using in proof /setup. If it's a custom profile please upload that too.

I hope this helps

if so, please "like" my reply and if you're OK now, please mark it as "correct", so that others who have similar issues can see the solution

thanks

neil barstow, colourmanagement.net :: adobe forum volunteer

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