[mattpavelle]

I'll run some of my own experiments on this today, but I'm initially concerned about color muting.

Specifically looking at the cat's eye example, in the bottom of the pupil area there's a bit of green (reflection?) in the lower pupil. In the original it is #293623 (green) - in the libjpeg it is #2E3230 (still green, slightly muted). But in the Guetzil encoded image it is #362C35 - still slightly green but quite close to grey.

In my experience people love to see colors "pop" in photos (and photography is where JPEG excels) - hopefully this is just an outlier and the majority of compressions with this tool don't lose color like this.

[jacobolus]

In general if you want to avoid any color changes in blobs a few pixels in size, you’ll want to take it easy on the compression, and take the hit of a larger file size in trade.

I suspect that if you give this algorithm twice the file size as a budget, that green color will come back.

[mattpavelle]

I agree, giving more file size may get us our colors back. And after some experimentation I'd like to be able to confirm something a bit abstract like, "Guetzli is good for reducing artifacts by sacrificing color" or some such snippet.

It would definitely have its uses as such. Or maybe it's great all around and I just found one bad example?

[JyrkiAlakuijala]

Guetzli sacrifices some chromaticity information, but tries to keep that in balance with the intensity loss. Guetzli sacrifices colors much less than the commonly used YUV420 mode -- the common default mode in JPEG encoding.

[natch]

Agree, that difference is very striking side by side to me at least. Maybe not to everyone, but I hope they have some people with very good color perception on their team so they'll be able to see the difference.