Unless you're targeting really old browsers, lossless WebP is absolutely worth it over PNG.
As a test, I have a set of 36 old MS paint Drawings, originally drawn on Windows 98SE, originally saved in bitmap format with a total size of 53.4 MB.
Transcoded to PNG format using FFmpeg and the highest -compression_level of 100, this same set of images takes up 403.8 kB.
Transcoded to -lossless WebP format using FFmpeg and libwebp with the maximum -quality value of 100 and maximum -compression_level of 6, the set of images takes up 174.8 kB.
Transcoded to lossless JPEG XL format using cjxl in the highest compression settings, the 36 images only takes up 126.6 kB.
Given the computing power required to decode JPEG XL images and their limited support, it may not make sense to use JPEG XL for non-archival purposes, but lossless WebP is an excellent middle-ground, achieving over 2x the compression level of PNG.
Lossless WebP has also been supported by all major web browsers since September 2022, when Apple finally added full support for lossless and animated WebP images. It really doesn't make sense to still be using PNG, unless you're targeting really out-of-date Mac or iOS devices. Having drawings and illustrations be 50% smaller (versus PNG) is huge!
As a test, I have a set of 36 old MS paint Drawings, originally drawn on Windows 98SE, originally saved in bitmap format with a total size of 53.4 MB.
Transcoded to PNG format using FFmpeg and the highest -compression_level of 100, this same set of images takes up 403.8 kB.
Transcoded to -lossless WebP format using FFmpeg and libwebp with the maximum -quality value of 100 and maximum -compression_level of 6, the set of images takes up 174.8 kB.
Transcoded to lossless JPEG XL format using cjxl in the highest compression settings, the 36 images only takes up 126.6 kB.
Given the computing power required to decode JPEG XL images and their limited support, it may not make sense to use JPEG XL for non-archival purposes, but lossless WebP is an excellent middle-ground, achieving over 2x the compression level of PNG.
Lossless WebP has also been supported by all major web browsers since September 2022, when Apple finally added full support for lossless and animated WebP images. It really doesn't make sense to still be using PNG, unless you're targeting really out-of-date Mac or iOS devices. Having drawings and illustrations be 50% smaller (versus PNG) is huge!