Recent content by Graeme Gill

Note that any difference in the profiles using -nI will show up only in the A2B0 and A2B2 tables. The theory is that Lightroom is using round trips through the A2B0 and B2A0 tables in its BPC heuristic.

I don't think Gamutvision will show anything useful, since it has previously showed that existing ArgyllCMS profiles have a perfectly good perceptual intent black level. The problem reported seems to be mainly in Lightroom. So best if someone who has this problem re-create a profile with...

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

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.

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.

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...

I'm not seeing that from your plots. Colorimetric I can see that the Argyll black is slightly raised, but that is to be expected with an accurate colorimetric profile - the lowest L* black is not neutral, so you get minimum dE clipping, which has a worse L*. If the Calibrite profile is giving...

Then I suggest that a customer of Adobe (i.e. someone who owns a copy of Lightroom) report the problem to them - I can't, since I'm not a customer! Or use some other software without this bug, instead of Lightroom to manage your printing color workflow. ArgyllCMS profiles match ICC...

Except that it provides exactly that for perceptual rendering. Setup your perceptual table for your source colorspace, and it will attempt to map your black to the lowest possible neutralish black that the printer provides. (If I remember correctly) the previous discussion and investigation...

Lightroom is broken then - either report the bug to Adobe, or use something else to print images. ArgyllCMS perceptual works perfectly well when used as intended - which is simply using it with the source profile it was created for, as per ICC expectations. BPC is not ICC spec. You'll get an...

Simply don't do that. Don't invoke (some unknown implementation of BPC) on ArgyllCMS Perceptual intent. It was never intended that it be used with such a hack, and in fact was specifically intended to avoid the need for BPC ! The profile doesn't do anything - it's the BPC that raised the black...

You mean full range of their colorspace. No printer will print L* = 0.

I tried to reproduce this using LittleCMS's implementation of BPC, but couldn't. It works as expected, and gives the same (good) black as not using BPC when using Perceptual intent. Looking through the thread it's not clear to me what is implementing the BPC that is showing this problem (i.e...

The colorimetric table seems to be pretty well behaved: icclu -ff -ir PX720_optimized.icm 0.000000 0.000000 0.000000 [RGB] -> Lut -> 4.248098 -0.397643 -5.411831 [Lab] icclu -fb -ir PX720_optimized.icm 0.000000 0.000000 0.000000 [Lab] -> Lut -> 0.102383 0.019198 0.000000 [RGB] icclu -ff -ir...

Without being able to see the measurement data and know what the profile making workflow is (i.e. the options used to create the profile), I really can't say. The aim generally is to create the darkest black point possible. But the main limitation may be the neutrality of the lowest L* value...