In general, Optimage can do automatic lossy (visually lossless) optimizations on JPEGs and PNGs, tries all possible image data representations (e.g. fast brute forcing of PNG delta filters), has some new tweaks to compression algorithms, converts to sRGB (tiny sRGB ICC color profile for JPEGs), handles more edge cases, and a lot of other small things. There are some other upcoming features, e.g. optimization of ICO and ICNS file types, lossless rotation of JPEGs according to Orientation meta in Exif.
In general, Optimage can do automatic lossy (visually lossless) optimizations on JPEGs and PNGs, tries all possible image data representations (e.g. fast brute forcing of PNG delta filters), has some new tweaks to compression algorithms, converts to sRGB (tiny sRGB ICC color profile for JPEGs), handles more edge cases, and a lot of other small things. There are some other upcoming features, e.g. optimization of ICO and ICNS file types, lossless rotation of JPEGs according to Orientation meta in Exif.
There's a good PNG test corpus at http://css-ig.net/images/png-test-corpus/png-test-corpus-2017.zip. Optimage – 276 201 bytes, ImageOptim – 297 561 bytes.