Participating Frequently

Question

P: Color artifacts in JPEG XL ProPhoto RGB

Forum|Forum|1 year ago
June 13, 2024
14 replies
10070 views

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

Windows

Show previous replies

apf102

Known Participant

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.

apf102

Known Participant

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

Genius

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.51142/#post-1340444

johnrellis

Genius

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-p/14678954

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

Rick Spaulding -

Legend

Update: Recommendations:

If using lossy compression, prefer using JXL-native color spaces such as sRGB, Display P3, or Rec 2020.
If you must use non-native color spaces such as Adobe RGB or ProPhoto, consider using Lossless (quality 13).

R

rudolfl27731976

Known Participant

I'm seeing artifacts I've not seen before when exporting in the JPEG XL lossy format. (90%) quality)

These a red blocks (I think 8x8 pixels size) around a strong blue colored bird.
See areas indicated by yellow areas on the picture below.
I compared it to TIFF and JPEG (90%) of identical of identical size (pixels), both are looking fine.
Increasing the JPEG XL quality to 100% doesn't solve it. Going to Lossless does.

When I started using JPEG XL, I have evaluated it and saw superior quality compared to JPEG of similar file size. These artifacts are new to me.

I'm using LR 14.1.1, Windows 11 computer.
See attached picture at 300% for easy vieweing. Unfortunately the artifacts are visible at 100% too.

Is this normal for JPEG XL? Have I overlooked it in the past? Is the contents of my picture so specific and causing this? is it a bug ? Are a few of the questions I have.
Can share the DNG file if you like.

johnrellis

Genius

@johnrellis

It is not as designed but rather a design limitation with the JPEG-XL. Comments from the engineers

"This is a quality limitation of JPEG XL when used with non-native color spaces in lossy mode."

I updated Rick Spaulding's post to reflect the correct workflow.

[This post contains formatting and embedded images that don't appear in email. View the post in your Web browser.]

@Rikk Flohr: Photography: "It is not as designed but rather a design limitation with the JPEG-XL. Comments from the engineers: "This is a quality limitation of JPEG XL when used with non-native color spaces in lossy mode.""

@Rikk Flohr: Photography, the "cjxl" program from the libjxl JPEG XL reference implementation doesn't produce these artifacts with ProPhoto RGB and lossy mode. So this points to a bug in LR's implementation rather than a limitation of JPEG XL. It would be interesting to get the engineers' perspective on why "cjxl" doesn't generate the artifacts.

To demonstrate with LR 14.1.1 / Mac OS 15.2:

1. I used LR to export a denoised DNG to the file x.png.

2. I exported x.png to x.jxl, with the options Image Format: JPEG XL, Quality: 100, Color Space: ProPhoto RGB, Bit Depth: 16 bits/component.

3. I used "cjxl" to generate x-cjxl.png from x.png, with the option --quality=99:

cjxl x.png x-cjxl.jxl --quality=99

The screenshot below shows x.jxl, x.png, and x-cjxl.jxl. There is no visual difference between x.png and x-cjxl.jxl, though there are quite noticeable artifacts in x.jxl:

You can download a catalog with all the images from here:

https://www.dropbox.com/s/q2kssve7f16gpt4/jxl-artifacts.2025-01-24.zip?dl=0

The exact "cjxl" command:

$ cjxl x.png x-cjxl.jxl --quality=99
JPEG XL encoder v0.11.0 [NEON]
libpng warning: iCCP: profile 'ProPhoto RGB': 0h: PCS illuminant is not D50
Encoding [VarDCT, d0.190, effort: 7]
Compressed to 30494.7 kB including container (5.369 bpp).
5504 x 8256,  14.558 MP/s [14.56, 14.56], , 1 reps, 12 threads.

The "jxlinfo" command shows that the image is lossy and in ProPhoto:

$ jxlinfo x-cjxl.jxl 
JPEG XL file format container (ISO/IEC 18181-2)
JPEG XL image, 5504x8256, lossy, 16-bit RGB
Color space: RGB, Custom, white_point(x=0.345705,y=0.358540), Custom primaries: red(x=0.734699,y=0.265302),  green(x=0.159600,y=0.840399),  blue(x=0.036597,y=0.000106)gamma(0.555315) transfer function, rendering intent: Perceptual
Brotli-compressed xml  metadata: 3381 compressed bytes

The warning "PCS illuminant is not D50" arises because "cjxl" thinks the white point of x.png's colorspace has x=0.345705, whereas ProPhoto's D50 white point has x=0.345704 -- probably a rounding error somewhere.

But otherwise, "jxlinfo" shows the colorspace of x-cjxl.jxl is identical to Prophoto RGB.