Hermann-Josef
Here's my understanding, which I believe is slightly different than what you
described...
A scanner profile provides a mapping between the scanner's device specific
RGB values and a device independent profile connection space, either XYZ or
Lab, both of which are mathematical models for the human perception of
color.
When you "assign" the profile to the RGB values that come from the scanner,
you are in essence giving human perceptual definitions to those RGB values.
Then when you "convert" the RGB values from the scanner profile to AdobeRGB,
you are changing the RGB numbers while maintaining the same human perceptual
definitions for the colors. It's the RGB values that are changing with this
conversion. After the conversion, you get new RGB values, now in AdobeRGB
space, that map as closely as possible to the same XYZ/Lab values that the
scanner's profile mapped to for those colors. So, while the RGB values are
changing, the colors that will be perceived by a human are being maintained.
One important concern with this conversion is the treatement of the target's
white patch. With a "relative" conversion, the scanner's RGB value
corresponding to the target's white patch gets converted to be pure white in
AdobeRGB, and other colors get adjusted a relative amount during the
conversion. With an "absolute" conversion, the target's white patch is not
converted to AdobeRGB pure white, it remains its own color, and AdobeRGB's
pure white for that file becomes the white of a theoretical perfect
reflecting diffuser.
Hope this helps.
And please correct me if I'm misunderstanding any of this.
Thanks.
- Brad
