Christopher Marshall schrieb: > All: > > I think I've basically answered my own question,"How should you attempt to > deduce a correct gamma > correction > value for your scanner with sane?" > > The procedure is this: > - open a graphics program like the gimp and make some blocks of solid color > (gray scale) > - I suggest hitting the following (R,G,B) values > (64,64,64) > (128,128,128) > (192,192,192) > - print the page > - scan it > - open the scan with a photoshop-like program like the Gimp > - measure the values from the corresponding blocks in the image.
Christopher, this way, you measure (and correct to some extent) the colour deviations of the *entire chain* image colour values -> printed colour -> scanned colour. But both '->', i.e. each "transformation" of the colours into a new "representation", introduces new errors. Especially, you must expect serious deviations by the print process. This does not help if you want to have "true colours" for a scan of a photo, since the photo has not been produced by the printer. I'd recommend to follow Gerard's recommendation to use IT8 targets for colour correction. With an IT8 target, you have a sort of a "calibrated image"; which you can scan, and using programs from lcms or gcms, you can "calibrate" your scanner, i.e. create an ICC profile for it. ICC profiles provide a far better way to get something similar to "true colours" than the comparatively simple gamma correction. Abel
