JPEG XL
Posted: Tue Feb 08, 2022 8:26 pm
Hello,
I have a question and a suggestion about JPEG XL
1) Question
It is not clear at all for me how to use the 2 compression sliders. There is one from 0 (lowest) to 100% (best), another one (compression) from 0 to 9, which can be moved independently. I made some tests, read some papers on the web, but was not able to figure out how they interact (it seems that one may counter-balance a little bit the other). No means to have something clearer, such as for JPEG (a single compression slider, along with chroma subsampling and possibly some other options specific to JPEG XL) ???
2) Suggestion (possibly due to a bug)
JPEG XL is assumed to be able to losslessly convert JPEG into JPEG XL (and back). I tried with the lossless option in the JPEG XL menu. This results in a huge file (about 5 X larger whereas JPEG XL files should be lighter) and the file obtained is not exactly the same (different CRC). By the way, the difference is tiny: an arithmetic comparison pixel by pixel shows me that some pixels have changed a little bit (not a big issue as this not perceptible by a human eye, but strange for a compression assumed to be lossless). I would like to suggest to add an additional entry in the JPEG lossless menu for "create a JPG XL lossless copy" which would result in smaller files containing exactly the same information as the original JPEG. Ideally, it would be very useful if the lossless compression option in the JPG XL window could perform the same when starting from a JPEG file, so that the transformation can be batched through the batch convert menu.
Thanks
Simon
I have a question and a suggestion about JPEG XL
1) Question
It is not clear at all for me how to use the 2 compression sliders. There is one from 0 (lowest) to 100% (best), another one (compression) from 0 to 9, which can be moved independently. I made some tests, read some papers on the web, but was not able to figure out how they interact (it seems that one may counter-balance a little bit the other). No means to have something clearer, such as for JPEG (a single compression slider, along with chroma subsampling and possibly some other options specific to JPEG XL) ???
2) Suggestion (possibly due to a bug)
JPEG XL is assumed to be able to losslessly convert JPEG into JPEG XL (and back). I tried with the lossless option in the JPEG XL menu. This results in a huge file (about 5 X larger whereas JPEG XL files should be lighter) and the file obtained is not exactly the same (different CRC). By the way, the difference is tiny: an arithmetic comparison pixel by pixel shows me that some pixels have changed a little bit (not a big issue as this not perceptible by a human eye, but strange for a compression assumed to be lossless). I would like to suggest to add an additional entry in the JPEG lossless menu for "create a JPG XL lossless copy" which would result in smaller files containing exactly the same information as the original JPEG. Ideally, it would be very useful if the lossless compression option in the JPG XL window could perform the same when starting from a JPEG file, so that the transformation can be batched through the batch convert menu.
Thanks
Simon