I know it's not necessary in JPEG, but some codecs (especially video and therefore video-codec-derived still image formats) have only 4:2:0 option. And if a cod

I know it's not necessary in JPEG, but some codecs (especially video and therefore video-codec-derived still image formats) have only 4:2:0 option. And if a codec chooses to use it, I'd prefer the test suite to require it done well. I've recently looked at it closely and found that almost every codec does chroma subsampling incorrectly, but the error is visible mostly in computer-generated graphics, and rarely in photos, and probably that's why nobody cared to fix it. https://github.com/mozilla/mozjpeg/issues/193 https://github.com/mozilla/mozjpeg/issues/193