I have had good experiences with https://github.com/shssoichiro/oxipng . Although, I suspect this wouldn't give you nearly enough space savings as jpg. Source: about 1 year ago

If you do want the file as a PNG (for transparency and a common format that's well supported), but don't want it so huge, consider something like oxipng. https://github.com/shssoichiro/oxipng. Source: over 1 year ago

Oxipng, pngquant and svgcleaner — optimizing images. Source: over 1 year ago

I wonder how `pngcrush` compares to `oxipng` (https://github.com/shssoichiro/oxipng). Personally, I use `oxipng` if I want lossless compression. However, most of the time, I use `pngquant` instead, since it gives significant size reduction even at `99%` (I can't even distinguish between the original and reduced image).

    pngquant --quality=99 --ext=.png --force file.png

. - Source: Hacker News / almost 2 years ago

Depending on your workflow it might make sense to export PNGs directly from Affinity and then reduce their size with a utility like Oxipng, which uses all your cores to find the best algorithm for each particular image. Source: almost 2 years ago

There may be some newer program that also does this but it reminds me of the old Kuadro. Source: over 1 year ago