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Some tips! Every time you edit a .jpg file, it has to be decoded and re-encoded, which leaves artifacts everywhere. Often artifacts occur along hard lines and edges, because compressing large open spaces is much easier and prettier than trying to detect borders between two colors. Do it enough times and the artifacts will grow their own artifacts. Hideous! Artifacting also happens every time a large .jpg is uploaded to sites that compress them. This includes Twitter and Telegram!
To avoid quality loss in edits, start by saving the file as a .png, which don't have this problem because they are vector graphics (the file memorizes the pathway of lines, it's...math). You can use maximum compression because .png compression only requires more time to compress to a smaller filesize - the image will remain the same quality.
The second tip is also a no-brainer: don't edit re-uploads. Find the original and edit that, don't use the telegram rip of a telegram rip of a twitter upload someone sent you. Telegram can compress and recompress images so many times they begin to INCREASE in filesize. It's miraculous. There *is* a "send without compression" function, but it won't show a preview of the image, so nobody uses it.
The final tip is more "restorative" than the others: use Selective Gaussian Blur. It's a filter that blurs each pixel with only its SIMILAR neighbors. There are two parameters: 1. Amount of blur 2. The maximum allowed difference in color and lightness between two pixels to blur them. How does this remove artifacts? When you blur everything but the edges of an image, the "sharpness" of the lines and edges between colors is retained, but the one-off pixel artifacts get recognized as "the same as" their neighbors and "kneaded back into the dough". You don't actually need to understand it, just zoom way in and fiddle with both parameters until you don't see artifacts any more - just try to keep both parameters as low as possible, or images will start to look "oily".
Uh oh, did you get rid of the artifacts but now your whole image looks wet? Use an Unsharp Mask. Same story here, just try to keep both parameters as low as possible while still solving the problem.
That's it. I've been going back and using these strategies to try and restore a few high-res .gifs, because gifs have a special property called "dithering" that makes them look like ACTUAL GARBAGE and is ENTIRELY OUTDATED BY ALL MODERN ANIMATION FORMATS. Maybe I will make a thread here for high-quality .webps at some point, we'll see. It's a very tiring process.
Edited at 2021/03/19 07:43:04
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