Support for JXL thumbnail/preview in new lossy DNG file format

[Carlos2311]

Is your feature request related to a problem? Please describe

Since the release of Adobe Camera Raw 15 (october 2023), the lossy DNGs created by Adobe software use JXL compression by default, not only for the data itself, but also for the embedded preview (previously, it used a jpeg embedded preview). So, it is not possible to see the embedded previews for these files anymore, which used to be a jpeg embedded preview. Also, the thumbnails for these files are not displayed in Windows File Explorer - just a generic image icon is displayed, the same for all the files, which I assume is related to Windows not being able to generate specific thumbnails from the preview.

I've asked ImageGlass developers for support for this new lossy DNG format, but he said I must report it here since he uses ImageKick.

I'm sorry I can't provide a link to more detailed specifications of this change since, as far as I know, this has been a sneaky move by Adobe which was not announced or documented anywhere for the general public (maybe it's in the official DNG specification somewhere). I had a hard time finding out what was going on.

I'm attaching a sample of the "older" lossy dng's, and the "newer" variant.

sample lossy dngs.zip

Describe the solution you'd like

I assume the solution is to provide support for decoding/displaying the embedded JXL previews for this newer lossy DNG files.

Describe alternatives you've considered

I've registered a JXL library, and I can display .jxl files, but these are .dng files with an embedded .jxl preview, so it won't work.
So far, the only way to see the contents of the file is to open them in Adobe Camera Raw, import them to Lightroom Classic or browse those folders with Adobe Bridge.

Additional context

(Sorry if this is not the place or the protocol to report this kind of issue - I'm not a developer or anything, just trying to notify the appropriate people - thanks.)

[dlemstra]

It looks like there is no support for this format in libraw (https://github.com/LibRaw/LibRaw). This project uses version 0.21.2 of that library. I think you should report this upstream.

[Carlos2311]

Thanks for your reply, dlemstra. I'm not a developer so I'm not familiar with most of this protocolos and jargon. Reporting upstream means to report the issue in this other project, same as I did here? Thanks in advance if you can clarify that.

[dlemstra]

The libraw project is a dependency of ImageMagick and in open source development that is commonly referred to as upstream. And yes what I meant to say is that you will need to ask for support in that project instead.

[Carlos2311]

Thank you, dlemstra.

[kmilos]

Note that just using the latest LibRaw version is not sufficient for JPEG XL support, it must also be built w/ the Adobe SDK option enabled.

[dlemstra]

I don't know if we can use the Adobe SDK, will need to check if we can and want to take this dependency. But it will probably take a while before I have time to research this.