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sindresorhus / Gifski

🌈 Convert videos to high-quality GIFs on your Mac
https://sindresorhus.com/gifski
MIT License
7.83k stars 293 forks source link

Artifacts on 0-20% quality with screen recording #261

Closed sindresorhus closed 2 years ago

sindresorhus commented 2 years ago

GIF: https://user-images.githubusercontent.com/170270/148274421-a1d41304-e418-45ea-b21c-69a45289afaf.gif

Source video: https://user-images.githubusercontent.com/170270/148274565-5ec81390-60fc-4eab-ad18-b2839deca842.mov

@kornelski Is there anything the gifski library can do about this?

kornelski commented 2 years ago

I don't think it's a bug per se — it is working as designed. When you ask for low quality, you get frames limited to very few colors. MPEG compression adds changes all over the place, which requires redraw of a large area, which then is a mess, because it isn't allowed to use enough colors to redraw it nicely.

This case could have been handled better if I optimized specifically for it, but I never did. The quality option is documented as: "1-100, but useful range is 50-100"

sindresorhus commented 2 years ago

As a temporary fix, what do you think of making the "Quality" slider range be constrained to 0.2...1?

kornelski commented 2 years ago

Yes.

sindresorhus commented 2 years ago

@kornelski With latest Gifski, I noticed a small artifact on the lowest quality. Notice how the blue rectangle at the top (which says "Open the Mac app store...") is stuck on all the frames. Not a big deal. Just wanted to mention it in case there's anything that can be done about it. It was a user that sent me this.

Screen Recording 2022-01-12 at 23 53 47 Gifski

Source video: https://user-images.githubusercontent.com/170270/149186875-13668834-b4e3-42c4-a478-15fc0608601d.mov

kornelski commented 2 years ago

This artifact is file size reduction in action. Transparent pixels are cheaper than white pixels, so not overwriting the background color is cheaper than setting it to white. The previous color is kept when it's "close enough", and at low quality, everything is close enough.

sindresorhus commented 2 years ago

I kinda feel that when the whole contents change (in the GIF when there's a page change), it should waste some white pixels to get a clean slate. But it's not a big deal.