alfter@nevada.edu (SCOTT ALFTER) (05/02/91)
I have a whole bunch of color pictures I'd like to send to my Imagewriter. I can hack the routines together to do the actual printing. (Full-color printing on the Imagewriter would be done in four passes with four ribbons--yellow, red, blue, black.) The problems I'm having relate to (1) separating the colors and (2) halftoning. First, the color information in the pictures gives you red, green, and blue. As I mentioned above, though, you print with red, yellow, blue, and black. What formulas should be applied to generate the color separations? After that, is there an efficient way to generate a halfway-decent range of halftones? A way to make 256 different shades would be especially nice, but I'll probably have to settle for 64 shades (8x8 matrix for halftoning at 72x72 dpi). Maybe the GS system software gurus can help; they have to do the same stuff in the Imagewriter II drivers, but any code examples must be usable on 8-bit machines (I'm writing the programs on my IIe). Scott Alfter-----------------------------_/_---------------------------- Call the Skunk Works BBS (702) 896-2676 / v \ 6 PM-6 AM 300/1200/2400 Internet: alfter@uns-helios.nevada.edu ( ( Apple II: GEnie: S.ALFTER \_^_/ the power to be your best!
meekins@anaconda.cis.ohio-state.edu (Tim Meekins) (05/02/91)
In article <1991May1.173724.13975@nevada.edu> alfter@nevada.edu (SCOTT ALFTER) writes: >red, yellow, blue, and black. What formulas should be applied to >generate the color separations? After that, is there an efficient way C: Cyan or blue M: Magenta or red Y: Yellor or (you guessed it) yellow. First RGB -> CMY Since CMY is the inverse of RGB, it's as easy as: C = 1-R M = 1-G Y = 1-B Now, to take advantage of the black ribbon: CMY -> CMYK, where K is black K = min(C,M,Y) from above C = C - K M = M - K Y = Y - K >to generate a halfway-decent range of halftones? A way to make 256 >different shades would be especially nice, but I'll probably have to >settle for 64 shades (8x8 matrix for halftoning at 72x72 dpi). Maybe >the GS system software gurus can help; they have to do the same stuff >in the Imagewriter II drivers, but any code examples must be usable on >8-bit machines (I'm writing the programs on my IIe). > Hmmm. Now dithering is a whole new ballgame. With a little work, I'm sure you can figure out ordered dithering. But, common use in printing is the Floyd-Steinberg error diffusion. Not something I can really go into in a post like this. Also, dithering is a lot more complicated when working with several colors, namely CMYK. Most algorithms are for gray scale dithering, not several-color dithering. -- +---------------------------S-U-P-P-O-R-T-----------------------------------+ |/ Tim Meekins <<>> Snail Mail: <<>> Apple II \| |> meekins@cis.ohio-state.edu <<>> 8372 Morris Rd. <<>> Forever! <| |\ timm@pro-tcc.cts.com <<>> Hilliard, OH 43026 <<>> /|
daveh@ccwf.cc.utexas.edu (Dave Huang) (05/02/91)
In article <1991May1.173724.13975@nevada.edu> alfter@nevada.edu (SCOTT ALFTER) writes: >red, green, and blue. As I mentioned above, though, you print with >red, yellow, blue, and black. What formulas should be applied to >generate the color separations? After that, is there an efficient way The color separations are relatively easy, but they don't seem to come out right... I think the problem is that the "real" names for the subtractive primaries are cyan, magenta, and yellow. However, the colors in IWIIs ribbon aren't exactly those colors, they're more like blue, magenta, and yellow. This tends to turn things that should be blue into a purplish color :( Anyways, C = 1 - R M = 1 - G Y = 1 - B K = min(C,M,Y) then C = C - K, M = M - K, Y = Y - K >to generate a halfway-decent range of halftones? A way to make 256 >different shades would be especially nice, but I'll probably have to >settle for 64 shades (8x8 matrix for halftoning at 72x72 dpi). Maybe I don't know about halftones though. 256 shades is definitely too much for the IWII though, your pictures would be too chunky. I forgot how many shades the GS/OS printer drivers do, but I think it's around 9 shades of one primary color... It's listed in the Toolbox Reference Vol. 1, near the end, if you get a chance to look at one. Anyone else have helpful comments?? >Scott Alfter-----------------------------_/_---------------------------- >Call the Skunk Works BBS (702) 896-2676 / v \ 6 PM-6 AM 300/1200/2400 >Internet: alfter@uns-helios.nevada.edu ( ( Apple II: > GEnie: S.ALFTER \_^_/ the power to be your best! -- David Huang | Internet: daveh@ccwf.cc.utexas.edu | "One with a face made of metal UUCP: ...!ut-emx!ccwf.cc.utexas.edu!daveh | should not use the word 'rust'" America Online: DrWho29 |