ArgyllCMS profiles: Black Point Compensation gives composite black when checked

[Ink stained Fingers]

Just keep these details in mind

BPC is always on for perceptual rendering intent, i.e., the checkbox setting has no effect.

This is copied from

http://www.gamutvision.com/docs/blackpoint.html



And read on here

https://www.myiro.com/de/blog/bpc

3. PERCEPTUALS REVENGE​

Unlike relative colorimetric the perceptual rendering intent can be freely defined by the developers of the ICC Profiling Engine. Thus it is very much possible to implement a gamut mapping which preserves the original images grey axis much better than BPC is allowed to do.

 

[Graeme Gill]

BPC is always on for perceptual rendering intent, i.e., the checkbox setting has no effect.

This is copied from

http://www.gamutvision.com/docs/blackpoint.html

That's a mistake in my view. BPC is not ICC, and Perceptual intent is the one where the profile maker has the most discretion to manipulate the color, so it is the least safe for a BPC algorithm to make assumptions about how it behaves.

The fact that the plots show that ArgyllCMS profiles give good L* values with Perceptual intent using gamutvision, even if gamutvision has BPC forced on, is consistent with lcms behavior - I don't see lcms BPC stuffing up on Perceptual intent the same way Adobe does.

 

[Ink stained Fingers]

@darshan ,

if you want to evaluate the black levels clearly do the tests you did above with ArgyllCms and Calibrite again with a paper of the matte/uncoated type with a weaker black level to start with - e.g. L* around 20 - or even plain copy paper and create the same displays for these profiles - ArgyllCMS and Calibrite. The explanations for the differences are given in this thread above to my understanding but become much more visible with that retest.

 

[Graeme Gill]

I can't reproduce any problems with Adobe Photoshop CS2 V9 BPC for Perceptual intent. BPC on or off makes no difference. So either this problem is specific to Lightroom, or Adobe have changed their BPC algorithm since Photoshop CS2.

 

[Ink stained Fingers]

So either this problem is specific to Lightroom,

All problems related to this context with BPC always on with the perc. RI refer to the print module and softproof function of Lightroom , Photoshop is not reported to have the same issues; Adobe implements this differently in their different products. Same for the saturation intent - it lacks in Lightroom but not in Photoshop.

 

[pharmacist]

Qimage has a particular mode called auto: that chooses between perceptual or relative colorimetric with the extra option to enable BPC.....I am not sure how the software chooses between those two rendering intents based on what algorithm.

 

[Ink stained Fingers]

Watch the video - it's about the out of gamut colors

 

[Graeme Gill]

It is probably worth re-visiting this problem in Lightroom using a print profile created using ArgyllCMS V3.2.0 and the colorprof -nI option. This may be a work around to the Adobe bug.

 

[pharmacist]

I presume the new colorprof option will eliminate the elevated black level when BPC is checked and the profile will print the darkest black possible.

 

[Graeme Gill]

I presume the new colorprof option will eliminate the elevated black level when BPC is checked and the profile will print the darkest black possible.

Unknown. It depends on what exactly is wrong with Lightroom. Since I don't own Lightroom, someone with it will have to test.