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Comment by kowbell | Hacker News Reader

I've always been curious about the distinction between JPEG and JPEG2000. From what I can find online, everyone says that the visual quality is better than JPEG, it just flopped due to slow adoption. Could you elaborate on your claim that it's worse?

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The technology is very different. Both translate the image into a representation where it's easier to remove "unimportant" data. JPEG is based on discrete cosine transform (DCT), JPEG2000 on wavelet transform.

Visually, where JPEG produces ringing artifacts, JPEG2000 produces blurriness. JPEG artifacts look "sparkly" and are often a reasonable replacement for the original texture, JPEG2000 artifacts look offensively dull (my opinion). I think, in theoretical speak, it's called "JPEG better preserves high frequency energy". You should be able to find side by side comparisons using your favorite image search engine.

I've found a nice example. Compare the lawn, the part above the arc (especially on the right) and the uppermost window on the two 0.17 MB images. There are parts that look like the JPEG2000 encoder inserted big blotches where details should be. JPEG2000 seems to be better at large, gentle gradients and strong discontinuities between solid colored regions. https://www.imagepdf.com/images/jpeg2000.jpg

My understanding is that JPEG2000 never really demonstrated, in experiment, that it was better than JPEG at the types of images and use cases which JPEG was already designed for (photographic images, lossy compression). This use case is such a dominant use case for the web. If you wanted similar quality levels for JPEG and JPEG2000, you often got similar file sizes. I could dig up some of the tests, but the basic gist of it is that at lower file sizes, JPEG2000 would get blurry and JPEG would get that funky blocky noise it gets.

This is the result of actual experiments with human subjects judging image quality.

I haven't really heard claims that JPEG2000 is better, actually. I remember people saying that it was "supposed" to be better, but not by people who dug into it and made comparisons with human eyeballs.

There were some images that would appear visibly better with JPEG2000, like photographs with those beautiful fields of defocused color. JPEG2000 captured those fields of color with all the smoothness they originally had.

Thanks to the power of internet we do not need to speculate; here is a comparison between image formats, JPEG2000 being represented by "OPENJPEG": https://wyohknott.github.io/image-formats-comparison/#sking*...

Subjectively I think JPEG2000 is better across the different images, at least at this "medium" size preset.

I should also point out that mozjpeg is considerably better than jpeg compressors that were around when JPEG2000 was introduced. I don't know if openjpeg is similarly improved.

IMO, they are closer than in other comparisons except you can still see some of the usual problems: e.g. in the "Cecret [sic] Lake" image on Medium: with JPEG there is a hint of ripple on the lake and most of the raggedness of the edges of the clouds is still there. With JPEG2000, the reflections on the lake turn into blotches and clouds have soft edges, even missing some large and obvious details. For some reason, it's quite disturbing to me. OTOH, JPEG2000 does a surprisingly very good job on the bushes. Maybe JPEG2000 could be actually good by allocating a little more bitrate to low contrast areas.

I actually prefer JPEG, esp. in small size. – Thanks for the Link!

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