P: Color artifacts in JPEG XL ProPhoto RGB

[Krzysztof37569275vhjb]

JPEG XL files with the ProPhoro RGB color space exported from Lightroom contain color compression artifacts. They appear in quality 100% and lower. Other color spaces do not have this problem.

Lightroom version 13.3.1

Windows 11 23H2 version 22631.3593

[reproo2773183]

Thanks John, don't suppose there is any news from the investigating team.

[johnrellis]

That report was just acknowledged by Adobe and its status set to Investigating:

https://community.adobe.com/t5/camera-raw-bugs/p-certain-raw-files-export-unusually-large-with-jpeg-...

(With the release of LR 14, it can take longer than normal to process incoming reports.) If you follow that thread, you'll get notified of any changes in status. Adobe rarely comments if/when an issue will be fixed, but they're very good at updating the status (whether they consider it a bug or feature request, if they need more information, when a fix is released).

[reproo2773183]

I've just done a little test with Photoshop 26.8

first I Exported a lossy 16bit AdobeRGB Jpeg XL from Lightroom to verify its still giving artifacts, which it was.

Next I opened in Photoshop a lossless 16bit ProPhoto Jpeg XL from Lightroom which does not have the artifacts.

Next I used Convert to Profile in Photoshop to Convert to AdobeRGB.

Next I Save As this to JPEG XL (embed profile AdobeRGB - yes) Lossy 100 16bit with all 4 checkboxes checked at the bottom.

Closed and Opened, no artifacts.

However the embedded Profile IS NOT AdobeRGB.

Its shown in the screengrab a long string of numbers starting D65.

I'm fairly confident this is a V4 icc.

Is the limiting factor the old V2 iccs?

[johnrellis]

"However the embedded Profile IS NOT AdobeRGB."

The "jxlinfo" utility distributed with the libjxl reference implementation shows the following for .jxls produced by Photoshop 26.8 from AdobeRGB images:

Color space: RGB, D65, Custom primaries: red(x=0.639997,y=0.329997),  green(x=0.210005,y=0.710005),  blue(x=0.149998,y=0.060004)gamma(0.454707) transfer function, rendering intent: Relative

These are the parameters of Adobe RGB (modulo round errors). I don't have access to the JPEG XL standard (for which the antediluvian ISO charges hundreds of dollars). But from casual reading, it appears that JPEG XL doesn't require a full ICC profile to be embedded in the file -- the parameters can be embedded instead.  The output above suggests that the file uses JPEG XL color-space representation rather than a full ICC profile.

[johnrellis]

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Since Photoshop 26.8 can export JPEG XLs in the Adobe RGB and Prophoto RGB color spaces without artifacts, this further diminishes the credibility of the Adobe engineers' unsubstantiated claim that the artifacts are a consequence of the JPEG XL standard.

Using the photo "x.png" in my previous posts, here are the results of exporting to JPEG XL with LR versus PS, with 16-bit lossy quality 100:

Adobe RGB, LR versus PS:

 

Prophoto RGB, LR versus PS: