Photoshop is smart enough to disable chroma subsampling[1] if it will screw up the image, it looks like jpeg.io doesn't do that.

One of the worst case scenarios for chroma subsampling is alternating black and red lines. Some monitors/TVs do 4:2:0 by default. It can cause problems...

https://plus.google.com/photos/photo/100697962438000631056/5...

[1] https://en.wikipedia.org/wiki/Chroma_subsampling

Hi, co-founder of jpeg.io and kraken.io here. Thanks for this, we're still in "kinda beta" right now and will have a fix in production shortly. In summary, that's not supposed to happen at all and there are highly likely some other nasties which we will be ironing out over the next hours.

for being "kinda beta" you have quite the claims up on your website

Thats kind of what the format is for.

jpeg.io may have lost on sharp lines, but it had WAY fewer artifacts than either of the other exports, and the blue was closer to the original compared to the Photoshop export. In my opinion, it's a better quality image.

Honest question: if I can't see the artifacts without zooming in, is there any reason why I should care? Of all the conversion results offered, the Photoshop export actually looks the best to my eyes, so I'm genuinely trying to understand why the jpeg.io result would be considered better quality in this particular case.

I don't need to zoom in or even look that hard to see the artifacts. Maybe that's me, or maybe that's the retina display on my MacBook, but that's why jpeg.io looks the best for me. If you can't see the artifacts though, I would say jpeg.io loses out.

For me, it looks like a different image. As in, I would never have expected that the differences to the original weren't a (bad) choice by the "designer" making the image. That seems risky, and in many use cases a worse kind of artifact.

Would it be worthwhile to compress the edges separately? I.e., use edge-detection + dilation + quantize + mask to get the edges, then compress that less aggressively, and overlay over the aggressively-compressed image?

That was your take away from the comparison? Wow ... I fail to see how the jpeg.io is worse than the other two examples.

Look closely around the red and yellow rectangles and just about and edge meeting the blue and you will see. Open all 3 and tab one to the next and you will notice the big difference.

upon first glance it looks like the lines are blurry in the jpeg.io one compared to the original and other two.

If you zoom in a bit that may still be the case, but it looks like the overall image quality is much better.

The photoshop export has significant artifacts visible, while the jpeg.io compressed image has far fewer visible artifacts. The tinypng version isn't jpeg compressed but shows dithering as you would expect from a GIF file.