Thanks to Stefan, Dan, and David for your replies. I'll look into all three approaches, but this looks most directly like what I had in mind.
My limited intuition seemed to suggest that since RGB is an additive color space, there might be a direct way to subtract a cast out of it. Regards. - John Mills On Sun, 31 Jan 2010, David Gowers wrote: > On Sun, Jan 31, 2010 at 12:50 PM, John Mills <johnmi...@speakeasy.net> wrote: ... >> I am printing a scanned image onto a slightly toned surface (heavy >> watercolor paper), and I would like to precompensate somewhat for the >> effect of printing onto this warm toned medium. How can I correct the >> image before printing to approach the same colors as a print on white >> paper, at least in the darker areas? ... > I suggest trying this: > 1. Create an image full of the color of the paper. > 2. Look at the RGB values of the color you chose (my test color was > 244, 242, 219) > 3. Open up the 'Levels' tool. select Red channel, type the appropriate > value (eg 244) in the rightmost field under the 'input levels' > histogram+gradient. select green, type appropriate value (eg 242), > select blue, type appropriate value (219), OK. > 4. The canvas should now be completely white #FFFFFF / 255, 255, 255, > and you should have an appropriate Levels preset stored to apply to > your pictures; you may want to save the preset permanently with the > '+' button next to the preset selector (after first selecting it) > Note: > This method will clip out detail of colors that are as bright or > brighter than the real paper color. This is basically unavoidable > according to your description of the problem. > HTH, > David > _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
