BTW, I've put a new version on http://www.tiac.net/users/rlk/print.tar.gz. This one improves the smoothness of regions of mixed Cc and Mm (light and dark cyan and magenta); that's about the only difference. Date: Thu, 28 Oct 1999 15:37:26 -0400 From: Michael Sweet <mike@xxxxxxxxxx> Robert L Krawitz wrote: > 4) The K->CMY code is distinctly tuned for the Stylus Photo EX > right now. Sorry, I don't have another color printer to play > with. > > This should be addressed, but it won't be unless we get testers. GCR and UCR can be a pain to get right. Here's a possible solution based on the CMYK generation code we're currently using in CUPS: ... This reduces the amount of black based on the saturation of the color (more saturated means less black), and uses a GCR function/lut to control the final amount of black. The intent of doing this isn't to improve saturation, but rather to minimize pixelation/graininess in bright (little ink) highlights. In fact, it's largely in UNsaturated regions (even light to medium grays!) that I want to eliminate the use of black altogether, to create a smooth texture. The other part of the problem is that an equal mix of CMY doesn't actually produce a neutral gray, particularly when the use of light inks is taken into account. Right now I'm using a ratio of K = C + 9M/8 + 3Y/2 to get a reasonable gray balance, and of course this will vary with different inks. A simple implementation might just use a cutoff level and ramp the values starting at the cut-off point, e.g.: int GCR[256]; int GCRlevel; for (i = 0; i < GCRlevel; i ++) GCR[i] = 0; for (; i < 256; i ++) GCR[i] = 1 + (i - GCRlevel) * 254 / (255 - GCRlevel); That's similar to my approach, although not with a lookup table (look for KDARKNESS_LOWER, which is your GCRlevel, and KDARKNESS_UPPER, which is an upper bound at which we simply use all black). Actually, kdarkness is a function of the other color intensities; the darker the other colors are, the more black mixes in. We're looking into doing something similar for CUPS 1.1 that will also provide a gamma (power) value for the GCR LUT. > 5) The Stylus Photo printing has become very slow for some reason > (at least at 720 dpi). On the other hand, the > microweave-induced banding has entirely vanished, yielding > much (arguably spectacularly) better quality. I'm not > positive exactly what did this, but it's not at the top of my > list of priorities to "fix". If it takes 30 minutes to print a > really high quality full-page print that doesn't seem so bad. > > Not to be fixed, since this "problem" improves output quality > substantially in the highest quality output mode. 30 minutes is way too long. I'm still wrangling with EPSON over the softweave algorithm; hopefully we'll be able to include the code in a future print plug-in/CUPS driver, which lowers print times significantly. I've seen prints made with softweaving, and I think that the 30-minute print job produces better quality than any softweave I've seen thus far. I'd like to offer it as an option for someone who wants the absolute maximum quality. I have some softweave stuff generated from other applications; even if you can't include it, I may be able to reverse engineer it purely from generated output. I think someone already has for Ghostscript. -- Robert Krawitz <rlk@xxxxxxxxxxxx> http://www.tiac.net/users/rlk/ Tall Clubs International -- http://www.tall.org/ or 1-888-IM-TALL-2 Member of the League for Programming Freedom -- mail lpf@xxxxxxxxxxxx "Linux doesn't dictate how I work, I dictate how Linux works." --Eric Crampton
