JPG vs compressed JPG vs WEBP - why WEBP isn't the smallest one?

Question

I have this image (photo taken by me on SGS 9 plus): Uncompressed JPG image. Its size is 4032 x 3024 and its weight is around 3MB. I compressed it with TinyJPG Compressor and its weight was 1.3MB. For PNG images I used Online-Convert and I saw webp images much more smaller even than compressed with TinyPNG. I expected something similar, especially that I read an article JPG to WebP – Comparing Compression Sizes where WEBP is much smaller that compressed JPG. But when I convert my JPG to WEBP format in various online image convertion tools, I see 1.5-2MB size, so file is bigger than my compressed JPG. Am I missing something? WEBP should not be much smaller than compressed JPG? Thank you in advance for every answer.

Answer 1

My experience is that lossy WebP is superior below quality 70 (in libjpeg terms) and JPEG is often better than WebP at quality 90 and above. In between these qualities it doesn't seem to matter much.

I believe WebP qualities are inflated about 7 points, i.e., to match JPEG quality 85 one needs to use WebP quality 92 (when using the cwebp tool). I didn't measure this well, this is based on rather ad hoc experiments and some butteraugli runs.

Lossy WebP has difficulties compressing complex textures such as leafs of trees densely, whereas JPEGs difficulties are with thin lines against flat borders, like a telephone line hanging against the sky or computer graphics.