Various "extreme" compression methods, compared to this dithered image on the solarpowered website of Low Tech Magazine, which was 42,4KiB and had a 16 color palette:

Original color file (830,8KiB PNG as served, 513,3KiB after optipng) and a version with heavy smoothing and edge enhancements applied in GIMP (524,3KiB after optipng). The latter will be used in other tests from now on, because the original became unreadable too quickly:

pngquant with Floyd-Steinberg dithering, 16 colors (88,9KiB) and 8 colors (68,6KiB):

JPEGs, generated by GIMP at compression quality 80 (86,6KiB) and 40 (44,8KiB):

Grayscale. Optipng (223,4Kib)

JPEGs, generated by GIMP at compression quality 80 (70,9Kib) and 40 (37,8Kib)

pngquant with Floyd-Steinberg dithering, 16 colors (93,8KiB), 8 colors (72,1KiB) and 4 colors (46,7KiB):

GIMP positioned dithering, 16 colors (78,8KiB), 8 colors (55,9KiB) and 4 colors (36,2KiB):

Pushed shadows, pngquant without dithering, 16 colors (67,8KiB), 8 colors (46,0KiB) and 4 colors (27,8KiB):

Pushed shadows, pngquant with Floyd-Steinberg dithering, 16 colors (97,3KiB), 8 colors (75,3KiB) and 4 colors (52,9KiB):

Pushed shadows, GIMP positioned dithering, 16 colors (81,1KiB), 8 colors (53,3KiB) and 4 colors (38,7KiB):

Low-tech magazine 16 color 42,2KiB PNG as a point of comparison again: