Re: ICC v4
Re: ICC v4
- Subject: Re: ICC v4
- From: Graeme Gill <email@hidden>
- Date: Thu, 17 Nov 2005 15:03:24 -0800
Rich Apollo wrote:
Question — does the gamut of the source really matter? Doesn't the
profile simply need to compute gamut compression from PCS to device
color space? I mean, regardless of the gamut of the source, the
destination colors are always coming from the PCS, right?
"PCS" has a very large gamut. For Lab its 0..100, -128..127, -128..127.
The XYZ PCS volume is even larger.
If you compress down from there when your actual image occupies a small
portion of the PCS gamut, your result will be very desaturated indeed.
Most images in output referred colorspaces are assumed to have been
adjusted to occupy as much of the gamut as possible, because the output
device is usually limited in its gamut. Because of this, it's usually
reasonable to assume the source colorspace gamut approximates the gamut
of the image. One of the limits of ICC V2 is that the destination profile
doesn't usually know the source colorspace.
CIE based and other very wide gamut or scene referred colorspaces
can't be relied upon to implicitly define an image gamut. To map
images in these spaces to an output device you either need to
determine the actual images gamut, have a gamut provided with
the image (just like an embedded ICC profile), or use an agreed
upon gamut (such as the ICC PCS reference gamut, or the scRGB Gamut
Boundary Definition in the case of scRGB).
Graeme Gill.
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| >Re: ICC v4 (From: Rich Apollo <email@hidden>) |