Maximum PNG Compression

Sixty-four colours sounds severe and is genuinely fine for a large class of images. Icons, flat illustrations, pictograms, simple charts and most brand marks are built from a deliberately small palette — often fewer than a dozen distinct colours plus antialiasing along the edges. Reducing to 64 leaves the flat regions untouched and only slightly coarsens the edge blending, which is invisible at the size these assets actually render.

What does not survive is continuous tone. Any smooth gradient — a shadow, a blurred background, a sky, skin — needs far more than 64 steps to look continuous, and at this level it will break into visible bands even with dithering active. Dithering trades those hard bands for fine noise, which reads better but is still a compromise rather than a fix.

Banding is easiest to spot in large areas of near-uniform colour, so check the smoothest region of the image rather than the busiest. Zoom to 100% rather than fitting to the window — browser downscaling hides banding convincingly, and an image that looks clean in a thumbnail can be visibly stepped at full size. Pay particular attention to edges where antialiasing blends a shape into its background, since those are where a shrunken palette runs out of intermediate shades first.

If the result bands, the answer is more colours rather than more dithering. Step back to 128 and compare: the file will be larger but usually still well under half the original, and on artwork that needed the headroom that is a better trade than noise. If even 256 colours bands, the image is photographic and belongs in a different format entirely.