Optimized images are too big

[confile]

I tried a lot of jpg image to optimize with image_optim.

It reduces the size but when I compare how the results of what facebook does are, these images are way smaller than what comes out from image_optim.

Is there a way to decrease the image size any further without reducing the quality?

[toy]

By default image_optim is lossless, so using all the tools it will only remove all unnecessary data and will try to optimise compression. But you can allow lossy optimisations using allow_lossy: true / --allow-lossy, and if not enough with default options, configure workers to reduce image size more like jpegrecompress: {quality: 0} / --jpegrecompress-quality=0.

As a small test I've uploaded a 2048×1536 941KB image to facebook and got same size 324KB image, using image_optim --allow-lossy --jpegrecompress-quality=0 I've got a 220KB image.
Visual difference in my case was hardly noticeable.
Comparing original vs optimised using imagemagick: mean error per pixel (normalized mean error, normalized peak error)
for facebook optimisation: 5.29145e+09 (0.000184438, 0.203922)
for image_optim: 5.96241e+09 (0.000240838, 0.262745)

The jpegrecompress worker will soon get more options like #103, so more flexibility to get the desired result.

[confile]

That is great thank you.