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

[johnrellis]

"I'm now thinking its during the conversion from the native space to the non-native space some of the maths/rounding doesn't allow for a number bigger than 1  or smaller than 0 and you get a blown or clipping artifact in one or more of the channels."

This doesn't explain why the "cjxl" program from the reference implementation "libjxl" doesn't have this problem.  

[reproo2773183]

because cjxl and Affinity don't produce artifacts, indicates its a Lightroom limitation.

As an example of clipping and apologies because its backward in that Lightroom works and Photoshop doesn't; Lightroom can choose Perceptual or Relative to convert between color spaces and the results are different in Print Preview.

If you try the same thing between two RGB profiles in Photoshop the results are the same because in the RGB to RGB scenario intent is always Relative and the gamut is clipped rather than scaled.

Sorry to ramble, it might just be that Lightroom can't do the something special with lossy JPEG XL because it was built to calculate/transform things in a certain way.

Why don't we see artifacts in the 1:1 preview of a pano DNG?, I take it 1:1 previews are not lossy JPEG XL.

[johnrellis]

"Why don't we see artifacts in the 1:1 preview of a pano DNG?, I take it 1:1 previews are not lossy JPEG XL."

A panorama DNG created by Photo Merge is a "linear raw" with the raw pixels represented as three channels (RGB) in the color space of the camera's sensor. The pixels are normally compressed using JPEG XL compression, but their color space is that of the camera. 

When you view such a DNG in Library, it is converted to Adobe RGB, which is used for all Library previews. When you view the DNG in Develop, it is displayed in the working color space of Develop, Melissa RGB, which has the same color primaries as Prophoto RGB except with a linear curve instead of Prophoto's gamma curve.

So viewing Library is different than exporting:

Raw photos to panorama to Library preview: Camera color space > JPEG XL compression in camera color space > JPEG XL decompression > Adobe RGB.

Exporting raws to JPEG XL format in Prophoto: Camera color space > JPEG XL compression in Prophoto

[reproo2773183]

rudolfl27731976 Which Color Profile were you Exporting to? See Rick Spaulding's  pinned reply.

I had the pink/red blocks artifacts, but they disappear if I used Display P3

[rudolfl27731976]

I exported to AdobeRGB. Same as for you, they disappear when I use Display P3. 
Ruud

[reproo2773183]

just a thought; until this is fixed; would it be worth limiting the user's choices of color space when exporting from Lightroom.

eg remove or grey-out AdobeRGB and ProPhoto, when selecting JXL lossy.

[Krzysztof Cisło]

There was no such problem in version 13.2. Next versions of Lightroom have broken JPEG XL (lossy ProPhoto).

[johnrellis]

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With the same test photo I used above, I see artifacts in LR 13.2 too (below). Unfortunately, the Adobe engineering team has already decided this is a limitation of the JPEG XL format when used with Prophoto, not a bug, and it's unusual for them to change their minds in such cases. In my example above, the "cjxl" program distributed with the reference implementation "libjxl" doesn't produce such artifacts, so I'm highly skeptical about the engineers' claim.

[Krzysztof Cisło]

Are you sure? I checked and I don't see artifacts on 13.2. See below.
Current version 14.1.1 on the left and 13.2 on the right:

I used to use ProPhoto JPEG XL lossy (95%) as a replacement for flattened TIFs. They took up much less space while providing the same quality. I have a workaround. Since Adobe won't admit or fix this bug, I use the "unofficial" portable version 13.2 on the side to convert TIFs to JXLs.

[johnrellis]

"Are you sure?"

See the 13.2 version here:

https://community.adobe.com/t5/lightroom-classic-discussions/p-color-artifacts-in-jpeg-xl-prophoto-r...

which has green artifacts around the light bulbs not present in the original or the version created by "cjxl":

https://community.adobe.com/t5/lightroom-classic-discussions/p-color-artifacts-in-jpeg-xl-prophoto-r...

[apf102]

Weird artefacts with jpeg xl exports + advice on best export format

expectated behaviour - high quality jxl file

actual behaviour - file has blocky artefacts and weird colour shifts

Lr Classic  13.5.1 in Win 11 and Lr 9.5.1 on iPad 

Hi. Two quick questions.

1) Does anyone know why I am getting these weird red artefacts on my Jxl exports? This is viewed on Lr Cc on my iPad. Original file was a NEF of a film negative. It was converted in negative lab pro. You can see the NEF displays fine. If I export from the NEF to a jxl I get similar red artefacts, though less pronounced. Other formats are fine. The jxl settings were 16bit compressed at 100% quality in ProPhoto colour space from LR Classic on Pc.

2) this is a workflow question. I tend to import and convert film negatives in Lightroom Classic, but for various reasons I like to edit on my iPad. This means the best workflow is to create a positive image for editing on iPad and getting rid of the raw (I have the negative so no biggy). I had been exporting to sRGB JPEG but was getting weird results when printing and of course you lose a load of depth.. Tiffs are way too large to use. The plan was to use 16bit jxl maybe with ProPhoto colour space, which seems to be about 25mb, but am getting the issue described above.

Any ideas much welcomed!

[johnrellis]

Re the workflow question, see my suggestion for syncing the NEFs with LR Cloud and then LR Mobile on the Ipad:

https://www.lightroomqueen.com/community/threads/workflow-issues-with-jxl-and-lightroom-classic.5114...

[johnrellis]

Re color artifacts in JPEG XL ProPhoto RGB exports, Adobe has acknowledged this bug:

https://community.adobe.com/t5/lightroom-classic-bugs/p-color-artifacts-in-jpeg-xl-prophoto-rgb/idi-...

The color spaces Display P3 and Rec 2020 don't appear to have the problem.

[johnrellis]

Moderators, @Rikk Flohr: Photography, please merge with this bug:

https://community.adobe.com/t5/lightroom-classic-bugs/p-color-artifacts-in-jpeg-xl-prophoto-rgb/idi-...

[apf102]

Thanks. Have replied on the other forum too.

RE the bug. I can make the artefacts appear if I export to JXL in Rec2020 16bit with quality set to 100%. It is only the uncompressed exports which seem to be fine. 8 bit also fine.

[johnrellis]

"I can make the artefacts appear if I export to JXL in Rec2020 16bit with quality set to 100%. "

Please share a sample NEF showing these artifacts, so Adobe has more to work with. My sample NEF shows no artifacts with Rec 2020 at either 90% or 100%:

[Krzysztof Cisło]

Are you sure? I checked and I don't see artifacts on 13.2. See below.
Current version 14.1.1 on the left and 13.2 on the right:

I used to use ProPhoto JPEG XL lossy (95%) as a replacement for flattened TIFs. They took up much less space while providing the same quality. I have a workaround. Since Adobe won't admit or fix this bug, I use the "unofficial" portable version 13.2 on the side to convert TIFs to JXLs.

[Krzysztof Cisło]

Sorry. I replied to the wrong post.

[apf102]

Hi. Apologies, I think I must have got the files confused. Tried to replicate with the JXL again but didn't get anything. HOWEVER, you can see some of the red artefacting when exported as JXL 16 bit, 90% quality and in the AdobeRGB Colour Space, which I think is what you saw too.

Have also noticed the JXL export defaults back to 8 bit however you set up the export (even when saved as a preset)

[johnrellis]

"Have also noticed the JXL export defaults back to 8 bit however you set up the export"

Coincidentally, I just filed a bug report about that, having observed it working on another JXL issue:

https://community.adobe.com/t5/lightroom-classic-bugs/p-export-window-doesn-t-remember-previous-sett...

[Glenn McDowall]

same behaviour for me with CR2, might suggest the bug is in the export.

[reproo2773183]

I'm still seeing these Lightroom bugs (both the blocky artifacts and reverting to 8bit in the Export dialog) using the CC2025 release apps Lightroom Classic v14.0.1, ACR v17.0 Photoshop v26.0

[apf102]

Same here. Have recently switched to Mac too and the issue happens there. Has anyone tried it on other software?

[reproo2773183]

Affinity Photo 2 can Develop to 16bit AdobeRGB then Export to Lossy Quality100 jxl, without artifacts, worryingly the file size is much smaller than Lightroom's (6.1MB vs 41MB) and also I couldn't find any Lossless option.

[johnrellis]

"worryingly the file size is much smaller than Lightroom's (6.1MB vs 41MB)"

That's a LR bug that Adobe hasn't acknoweledged -- LR's JPEG XL exports are way too large compared to other apps:

https://community.adobe.com/t5/lightroom-classic-discussions/p-certain-raw-files-export-unusually-la...