Jpegli has the possibility of using XYB. By default as by being just a replacement of mozjpeg or libjpeg-turbo it doesn't.
I believe Jon has compared jpegli without XYB. If you turn XYB on, you get about 10 % more compression.
Jpegli is great even without XYB. It has many other methods for success (largely copied over from JPEG XL adaptive quantization heuristics, more precise intermediate calculations, as well as the guetzli method for variable dead-zone quantization).
disclaimer: I created the XYB colorspace, most of the JPEG XL VarDCT quality-affecting heuristics, and scoped jpegli. Zoltan (from WOFF2/Brotli fame!) did the actual implementation and made it work so well.
I believe Jon has compared jpegli without XYB. If you turn XYB on, you get about 10 % more compression.
Jpegli is great even without XYB. It has many other methods for success (largely copied over from JPEG XL adaptive quantization heuristics, more precise intermediate calculations, as well as the guetzli method for variable dead-zone quantization).
disclaimer: I created the XYB colorspace, most of the JPEG XL VarDCT quality-affecting heuristics, and scoped jpegli. Zoltan (from WOFF2/Brotli fame!) did the actual implementation and made it work so well.