Re-optimize images with new encoders

Currently, I got the best results from libwebp 1.6.0 (2025-07-07) using cwebp -lossless -m 6 -q 100 something.png -o something.webp . Compared to libwebp 1.5.0, 1.6.0 gave better compression on 38 images, worse compression on 3 images (Clerk, Shah, and Stanlow), and the same compression on 9 images. Each of the images that were the same size were actually the same file with the same sha256 hash.

Other encoders I should try.

libwebp: I should try reencoding all images when the newest version is at least one year old, or two years if I switch to JXL before then.

https://chromium.googlesource.com/webm/libwebp/+/refs/tags/v1.6.0

zopfli 1.0.3 (2019): the repository is archived as of 2025, so I won't need to retest this one.
Other png encoders and converters, including ImageMagick, GraphicsMagick, pamtopng and pnmtopng.
libavif with libaom: Previously it has given worse results than libweb. The other AV1 encoders can't do lossless at all. I should retest when the newest vesrions of both libavif and libaom are at least two years old. As of 2026-03-05, the newest versions are libavif 1.4.0 (2026-03-04) and libaom 3.13.1 (2025-09-05)

https://github.com/AOMediaCodec/libavif/releases/tag/v1.4.0

https://aomedia.googlesource.com/aom/+/refs/tags/v3.13.1

libjxl: I need to wait for browsers to support it.
A potential AV2IF: I need to wait for it to exist and for browsers to support it.
giflib? I could only use this for grayscale images and color images with at most 256 distinct colors. As of 2026-02-25, all the color images have well over 256 colors, with the smallest number of colors being in Hemmel's image, with "only" 1834 distinct colors. I don't know how to use giflib to encode an image, but I can use different gif converters including ImageMagick, GraphicsMagick, and pamtogif.

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