Change colored pngs to jpg and reduce pngs
if png has rgb colorspace
if png colorspace is not optimized palette
convert to HSB and get saturation
if saturation is lower than 5% convert rgb png to grayscale png
if saturation is higher than 5% convert color png to quality 80 jpg
The Magick version is using only ImageMagick
The Pingo version is using pingo for smallest b&w jpg size