written by Original Real Color Wheel by Don Jusko, posted with his permission.
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Printers and plotters use the Computer's RGB color wheel and convert it to the printer's CYMK color wheel. They look almost the same, but not exactly. It's better to change the RGB to CMYK and adjust the CYMK. It's best to convert a RAW image directly into CMYK. Printing any converted RGB profile has some printing problems.
written by realcolorwheel.com
Intensely layered magenta isn't possible because the full depth of the pigments ink won't print with only one coat without effecting the rest of the print, even with the extra Light Magenta ink. CMYK adds black ink at this point.
RGB prints what looks on the computer like a perfectly balanced color wheel, and shifts the cyan and magenta 30 degrees in the print. This expands the Green to Cyan range and shortens the Magenta to Red range. WHAT YOU SAW IS NOT WHAT YOU GOT.. on your printer. Also the printer will not print the higher RGB gamma ranges of color.
The CMYK Real Color Wheel you see on your computer is what you will get on your printer or plotter. It looks much duller in comparison to higher gamma RGB realcolorwheel, but the CMYK is the gamma range that is possible and it is what the printed image will look like. The RGB color system has a much higher color gamut, much of high end color is lost in CMYK.
Give the plotter a CMYK image and profile as opposed to giving the printer an RGB image of higher gamma and letting the printer/plotter convert it. It won't correct the color shift of magenta and cyan, that takes an original CMYK image.
The newer plotters give more to play with, with as far as matching colors to a painting or photo. Longer ranges of colors can come into play. For instance, Cyan and Yellow pigment or ink must cover from cyan to yellow in both CYMK and RGB. That's 130 degrees plus the extra 30 degrees because of the RGB color shift. The colors between Green and Yellow are limited by at least 15 degrees. The new plotters give the option of adding another color to CYMK. An extra pre-made Green to mix with Yellow, that evens out the colors available to be reproduced in the green to yellow range. It's not perfect, but it can help. I didn't like it.
The most useful combination of color in nature painting is green and a yellow/orange/red mixture. Green and Magenta make a neutral black from color, the shadow color of green.
Orange is the other color that is hard for the printer to match because of the 30 degree color shift in RGB and the muddiness made from the opaque yellow and transparent Magenta mixed wet. Orange is the second extra color available to my plotter. Having an extra orange makes a greater range of browns and better green/orange color combinations and evens out my ink usage. It works, but after changing out my colors to orange and green and testing it out I changed back to my light cyan and magenta.