Lars Aronsson wrote:
For example, the image http://runeberg.org/img/nfad/0670.4.png is 240 kbytes in 150 dpi 16-level grayscale PNG but only 200 kbytes in 600 dpi bitonal TIFF G4. The difference between 150 dpi grayscale and 600 dpi bitonal becomes very clear when you try to print the page on a 600 or 1200 dpi laser printer.
Have you tried a comparison against a 600 dpi bitonal PNG? The DEFLATE compression used in PNGs may or may not be as effective for bitone images as G4, but it should still handle them pretty well.