Use oxipng in optimize_images

[fmarier]

As mentioned in this blog post and used in this script, oxipng (which is not yet in Debian) is a rewrite of optipng in Rust. It focuses on improving performance, but it might also lead to better compression. To be tested.

[fmarier]

I tested this on a small image and these are the results I got:

• original.png: 13737 bytes
• optipng.png: 11191 bytes (optipng -o9)
• oxipng.png: 11240 bytes (oxipng)
• oxipngmax.png: 10658 bytes (oxipng -o max -Z -a)
• smallest.png: 10234 bytes, the result of either:
  • optipng -o9 and advpng -z -4, or
  • oxipng and advpng -z -4, or
  • oxipng -o max -Z -a and advpng -z -4

In other words, by itself, it's better than optipng, but it's still not as good as using optipng and advpng together. There doesn't seem to be any need to swap optipng for oxipng if one uses advpng afterwards.