Not using subsampling

[olafura]

I've used gimp with subsampling 4:2:0 and get better compression than guetzli. Is it possible to have that option?

[robryk]

Thanks for taking your time to investigate Guetzli.

Would you mind sharing an image (or, better yet, a few) and quality levels at which you notice this? It will be helpful to understand what's happening.

[istvan-ujjmeszaros]

You can try with any image. I am using RIOT (Radical Image Optimizer) to convert png to jpg and the result is smaller and has better quality compared to Guetzli, with every image I have tried so far (not too much, but I am not happy with the results at all so I am just waiting if it gets better). FYI in RIOT I am usually setting the quality for 92%-94% (based on the image, the higher is usually required if there is text on the image) and the subsampling for 4:4:4 (if there are lot of reds on the image) or 4:2:2, sometimes 4:2:0 (if there is no red or green on the image). 4:1:1 produces very bad results so I am never using that. Ah, and these are usually small images, like 600x200. But I have attached a bit larger one that has better result with RIOT (but I was using 80% quality for that one image - tried 84% with Guetzly but it wasn't looking good).