Date: 13 Jul 84 11:16:41 PDT From: Plass.pa Subject: JaMImager colors To: ImagingInterest^ Reply-To: Plass cc: Plass JaMImager has been changed to allow Color separations to be done. This does not live up to the goal of device independence, but it is a way to get nice pictures out on the color Versatec (it should work for Lilac as well). This involves an incompatible change in the way halftone screens are specified when creating PD files. It used to be that you had to specify the screen before the pd file was opened. Now you must specify it it after opening the PD file, and you may change it while drawing the picture into the PD file. It is subject to the regular saving and restoring effects of .dosave. Here is an example that prepares three AIS separations for the color versatec: (Wong.jam) = (screenFreq) 30 .def (wong.pd) .opencolorversatecpd .newtoner (black . . . ) .print {0.55 screenFreq 45 .setdotscreen 0 808 72 72 .maskrectangle 288 808 .setxy (TimesRoman) 20 .setfont (Wong.AIS Plass.pa July 13, 1984).drawtext }.cvx .dosave .newtoner (cyan . . . ) .print {0.55 screenFreq 60 .setdotscreen 72 808 72 72 .maskrectangle (/pixel/images/wong-red.ais).setsampledcolor 0 0 600 800 .maskrectangle }.cvx .dosave .newtoner (magenta . . . ) .print {0.55 screenFreq 30 .setdotscreen 144 808 72 72 .maskrectangle (/pixel/images/wong-grn.ais).setsampledcolor 0 0 600 800 .maskrectangle }.cvx .dosave .newtoner (yellow . . . ) .print {0.55 screenFreq 0 .setdotscreen 72 144 .add 808 72 72 .maskrectangle (/pixel/images/wong-blu.ais).setsampledcolor 0 0 600 800 .maskrectangle }.cvx .dosave (closing) .print .closepd (.) = Some notes: Each separation should use a screen at a different angle, to get halfway decent color reproduction. The angles given above are more or less the standard ones used in the printing industry. The dot frequency (30 per inch) is about as high as you can use before seeing quantization effects on smoothly varying shaded area, but the rosettes are very noticable close-up. If you are doing only flat areas, you can get by with a finer screen. You may want to use custom bricks to generate special stipples. When putting out AIS separations, print each separation on its complementary toner. The color separations are always put out in the same order (black, cyan, magenta, yellow). The .newtoner operator says you want to start a new separation. I am told that the Versatec PD software gets confused if you put out a separation with nothing in it. I'll fix that sometime, but in the meantime it's probably a good idea to have some colored squares on each image to have some idea of how well the Versatec is feeling. Note that if you want a particular color, you have to figure out what grays to use in each separation. Putting your name somewhere near the top or bottom of the image is a good idea, at least until I get separators implemented in the PD interpreter. Here are the ways you can now specify halftone screens in JaMImager: .setlinescreen .setdotscreen . . . . . . . . . . . . . . . . . . .setcustomscreen .setaisscreen ’sets a line screen, the angle being in degrees. This is nice for ordinary resolution xerography. sets a dot screen. The ratio parameter controls how symmetrical the dots are  0.0 and 0.1 will yield lines screens (in different directions), and 0.5 gives symmetrical dots. The tij are reals in the range [0.0..1.0), and are the threshold values for the halftoning brick; n and m are the number of scans and the number of dots per scan in the brick, and phase says how much to shift the bricks between rows. Note the custom screen is dependent on the resolution and scan direction on the printer. uses an AIS file the specify a square, rotated brick. ÊŒ˜šœ«Ïeœî˜žJ˜J˜J˜ J˜Jšœ˜Jšœ˜˜!J˜J˜J˜KJ˜ —Jšœ˜˜!J˜Jšœ,˜,J˜J˜ —Jšœ!˜!˜!J˜J˜,J˜J˜ —Jšœ ˜ ˜ J˜$Jšœ,˜,J˜J˜ —Jšœ˜J˜J˜J˜J˜—˜ J˜øJ˜J˜TJšœ¬˜¬J˜gJ˜“˜DJ˜šœÏkœ žœ˜1J™aJ˜—šœžœžœ žœ˜>Jšœ¯™¯J˜—JšœÏdœŸœ Ÿœ˜JšœŸœŸœ Ÿœ˜J˜JšœŸœŸœ Ÿœ˜šœžœžœ žœ˜/JšœŸœ¼™ÃJ˜—šžœ žœžœ žœ˜AJ™5———J˜—…— &