Re: Scanner Color Space
Re: Scanner Color Space
- Subject: Re: Scanner Color Space
- From: email@hidden
- Date: Fri, 15 Nov 2002 12:23:35 EST
>
Scanners don't really have a gamut; they have a response range.
Here's another way of looking at it: It is true that the color gamut of a
scanner (or digital camera) is somewhat arbitrary as it depends on the
transformation between scanner RGB and CIE coordinates. However, since the
scanner has spectral responses that are different from those of humans, there
will be a certain amount of observer metamerism, since no scanner perfectly
satisfies the Luther condition (scanner and human responses are linearly
related). This means that the scanner will see colors differently from a
human and this therefore effectively reduces the scanner gamut. Obviously the
point of a profile is to compensate for this effect. But the scanner profile
will always be imperfect at characterizing the scanner gamut. An extreme case
is where a color's spectral reflectance is in a range where the scanner has
no sensitivity. It will be reproduced as black because the scanner just can't
"see" this color. Of course, input colors that exceed the range for which the
scanner has been set up (or profiled) will also be compressed or clipped
therefore further limiting the scanner gamut. Less extreme cases are more
common and lead to significant colorimetric errors and therefore less certain
color gamut.
Eric Walowit
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