Support JPEG XL compression in DNG

[kmilos]

Just added in DNG 1.7, and is allowed for e.g. 3-channel LinearRaw photometric interpretation.

Available (C) implementations:

https://github.com/libjxl/libjxl (reference)
https://github.com/lifthrasiir/j40 (single header, public domain)

[cytrinox]

Good hint. Disappointed that they only specified it for LinearRaw but not for CFA.

[kmilos]

Disappointed that they only specified it for LinearRaw but not for CFA.

Check the new ColumnInterLeaveFactor as well.

[kmilos]

For example, appears as the enhanced linear raw subimage in new Adobe AI denoised DNGs.

[kmilos]

And now also looks like it's in Samsung Galaxy enhanced ExpertRAW DNGs.

[Entropy512]

Check the new ColumnInterLeaveFactor as well.

The stated purpose here describes a nonstandard/proprietary method of encoding raw sensor data I remember seeing a few years ago, but can't find at the moment (and in the process, ALMOST makes it standardized except for one issue, see my last comment) - Take the individual color planes from the CFA, and store them as adjacent images in a monochrome JPEG. A potential use case for this would be hardware that was severely IO-bound but had a reasonably performing hardware JPEG engine (I can think of one specific camera that would REALLY benefit from this, as it has a hardware JPEG engine but USB 2.0 and stores bracketed shots from 25 10-bit sensors, which wouldn't lose too much with nonlinear encoding to 8 bits/sample...), or to allow lossy storage of CFA data with JXL.

It seems that JXL + the new RowInterleaveFactor and ColumnInterleaveFactor would support exactly this, but wouldn't that technically require PhotometricInterpretation to be 32803 (CFA)? e.g. "so close yet so far" here.

[kmilos]

Looks like iPhone 16 started using it as well.