majidi@paul.rutgers.edu (Masoud Majidi) (03/28/91)
A while back somebody posted on this newsgroup a mapping from RGB values to gray intensities. I was wondering if there is a good mapping in the reverse direction. If you know how to get RGB values out of gray intensities I appreciate it if you let me know. (I don't know if this would make any difference but my images are from body organs) Thanks a lot, Masoud Majidi(majidi@paul.rutgers.edu)
kempkec@mist.CS.ORST.EDU (Christopher Kempke) (03/28/91)
In article <Mar.27.18.06.14.1991.28546@paul.rutgers.edu> majidi@paul.rutgers.edu (Masoud Majidi) writes: > >A while back somebody posted on this newsgroup a mapping from RGB >values to gray intensities. I was wondering if there is a good >mapping in the reverse direction. If you know how to get RGB values >out of gray intensities I appreciate it if you let me know. I don't think this can be done in the general case; the intensity value is a combination of three values for the red, green, and blue components, something like this: Grey = .299 * Red + .587 * Green + .119 * Blue, or I = .299r + .587g + .119b for brevity. Now, consider an intensity value of .500 (medium grey): There are clearly many mappings back to R, G, and B. R = .10, G = .78, B = .10 or R = .20, G = .70, B = .20 or any of an infinity of others. The possible exception to this is if you knew EXACTLY the palette of colors from which the greyscales were derived, in which case there MIGHT be a single unique answer to the equation among the options available to you. However, this would work only for a relatively small or carefully-picked palette; and is unlikely to be true in most situations. --Chris