QL-600: Huge quality difference between Windows driver and this

[V10lator]

The left one has been printed from a Windows VM while the right one has been printed from Linux using this driver. Both drivers had been configured to print in high-quality but as you see it's still day and night.

Here's the image file used for this:

[philpem]

This isn't a bug in the driver.

All the driver does is take the bitmap (1-bit black-and-white a.k.a. bitonal) data provided by CUPS and turns it into printer commands. The conversion from colour photo to bitonal is CUPS's doing -- or rather the PostScript renderer it uses (pstoraster). See apple/cups#5092 and apple/cups#4820.

The only way this could reasonably be improved is by rewriting rastertoptch as an 8-bit greyscale filter and implementing Floyd-Steinberg (and probably threshold) dithering in the driver itself. But if we're taking that route, the smarter money seems to be in adding P-Touch support to Michael R. Sweet's lprint driver: michaelrsweet/lprint#15

[ValdikSS]

OpenPrinting/cups-filters#642