jpegli strategies for (certain?) jpg

[TPS]

@JayXon https://github.com/google/jpegli/blob/main/README.md#encoder-improvements (last §) notes that it has compression optimizations for a certain subclass of jpg.

Support for more efficient compression of JPEGs with an ICC profile representing the XYB colorspace. These JPEGs will not be converted to the YCbCr colorspace, but specialized quantization tables will be chosen for the original X, Y, B channels.

Possible to implement here?

[JayXon]

I don't think that's lossless though?

[TPS]

You know, I'm honestly not sure. I know that cjxl does have a lossless mode for typical JPG, & I think I read that into jpegli. I'll open an issue there if I can't find docs directly addressing it definitely.

[TPS]

After a quick search & read, I'm almost certain jpegli has no lossless mode of any kind, but I've asked officially in the appropriate issue, so we'll know more shortly.

[TPS]

Definitively no, but, if jpegli were to develop some lossless JPG techniques, that's the issue they'd be noted.

notes that it has compression optimizations for a certain subclass of jpg. Is that lossless, @ least?

No, XYB jpegs are lossy. More efficient compression than regular jpegs but still a lossy process. Jpegli is not a transcoder like jpegtran.

Originally posted by @Galaxy4594 in google/jpegli#10 (comment)