On 09/23/2016 11:57 AM, Ross Martinek wrote: > Thanks for jogging my memory. I think what I was thinking is that Adobe had > color palettes based on those catalogs, intended to produce printed colors > that matched the catalog. Like I said, it’s been a long time.
Those catalogs would be Pantone ones. They are usually most relevant when printing vector graphics, i.e. silk screen or offset printing. Printer's inks have Pantone values printed on their labels, and very precisely match the color chips on Pantone reference cards. I have seen "Pantone to HTML color" charts on the network, and they are better than nothing but far from precise. "HTML color" means hexadecimal RGB, which is also the GIMP's native color model. RGB stands for Red, Green and Blue. It is an "additive" color model, applicable to mixing colored light sources. Example: TV screens and computer monitors. LAB stands for Luminance, Red/Green, Blue/Yellow. It is based on studies of human color perception and is more or less universal, but no monitor or printer can duplicate this color space directly - it has to be exported to RGB (monitor) or CMYK (printer) for display. CMYK stands for Cyan, Magenta, Yellow and Black. It is a "subtractive" color model, applicable to mixing ink or paint colors to control the color of reflected light. When people start talking about computer programs that can "natively edit in CMYK", try not to groan: The only way to edit images in CMYK is with a paintbrush or comparable tool, because on a monitor you see the image in RGB no matter what format the program is reading from and writing to. An RGB image can be exported to or imported from a file with CMYK data, via a filter based on the intersection of RGB and CMYK values in LAB color space. But "what you see" on the monitor is not exactly "what you get" on the printed page. Upcoming versions of the GIMP with GEGL under the hood will support /much/ higher resolution RGB color, improving the potential color match between screen and paper versions of a given image. (GIMP layers can also include an Alpha channel for transparency; hence "RGBA" values.) In recent times I have had no problems with color management for print; PNG files imported to Scribus and saved as PDF come out looking like I want them to when printed. A decade ago, this was not always the case. I believe that LCD monitors and improvements in color conversion algorithms probably account for this. To get the best available color rendering, first check your monitor. If a color profile is available from the manufacturer, get it and install it on your workstation machine, and make sure the GIMP knows about it: Edit > Preferences > Color Management. This will tweak your video output for "best results." An alternative to this is to glovally disable color management and tweak your monitor by hand, see: http://www.lagom.nl/lcd-test/ Color perception is also a factor: The more neutral gray you see around an image, the less your eye and brain will distort the colors in the image. Conversely, if you know that a bunch of images you are working on will be displayed on a colored background - say a web page or brochure - you can set the Canvas Padding color in the GIMP to that color, and see your images in progress in their native color context: Edit > Preferences > Image Windows > Appearance. The GIMP includes a filter that converts the visible image to CMYK layers, and the result can be exported as a CMYK TIFF file. This may facilitate color adjustment at the print shop, and any commercial printers who still demand "Adobe Formats Only, or take your filthy money elsewhere!" will usually accept CMYK TIFF files without complaint. Color printing used to be a bit of a major nuisance, but lately not so much - depending the use case, your mileage may vary. The remaining problem is color resolution: If you have a big, subtle gradient you have to get just exactly right, you are going to see banding on your monitor and in the printed results. The upcoming GEGL based GIMP color model, with resolutions up to 64 bit floating point, should put a stop to that nonsense. :o) _______________________________________________ gimp-user-list mailing list List address: [email protected] List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list List archives: https://mail.gnome.org/archives/gimp-user-list
