Kind of, but JPEG converts image data to its own internal 3 came channel colour space before applying DCT. It is not compressing the R, G and B channels of most images. So a multichannel compression is not just compressing each channel separately.
JPEG 2000 supports lossless mode.
I can’t comment on the others, but PDF to JPEG should be easy enough. ImageMagick, which another commenter suggested, is possible but not user friendly. However you can just open the PDF in many applications and export it as an image. Adobe Acrobat and Photoshop can do it. GIMP probably too.
I’m a last ditch effort you can even just open the file and screenshot it.
And this time it is indeed typical
The canine revolution has started. They’ve been playing us for fools, making us think it’s the feline population we had to fear, all the while planning this.
You could also try ecosia. I’ve been using them for years, and since a few months Vivaldi has a deal with them too.
“And while Spectral JPEG XL dramatically reduces file sizes, its lossy approach may pose drawbacks for some scientific applications.”
This is the part that confuses me. First of all, many applications that need spectral data need it to be as accurate as possible. Lossy compression in that might not be acceptable.
More interestingly (and I’ll read the actual paper for this): which data will be more compressed? Simply put, JPEG achieves its best compression by keeping the brightness but discarding colour. Which dimension in which spectral space do the researchers think can be more compressed than others? In this case there is no human visual system to base the decision on.