Graham Sutherland / Polynomialfor PNG images I attempt an indexed colour encoding, subtractively combine it with the original image data, threshold the luma and chroma deltas to get a per-pixel "different/same" value, sum those, and if less than 1% of the image is affected then I keep it. if not I fall back to max compression RGB888. (I don't use transparency in blog images)
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.