Re: Perceptual Javex
Re: Perceptual Javex
- Subject: Re: Perceptual Javex
- From: Graeme Gill <email@hidden>
- Date: Fri, 22 Sep 2006 13:26:15 +1000
eugene appert wrote:
Thanks for your answer. According to Colorthink this profile is a16
bit, 25 grid point table based profile, L*a*b* PCS Lut. Colothink also
describes it as a scnr type, I am not sure what that means.
It means that the profile class is an input profile.
> Though it
shows a white and black point of L*0 and L*100 in the devise color space
area , it describes the PSC white point as 0,9462, 1,,08249 in ICC
technical attributes. However under the tag table tab, it describes the
media white point as:
XYZ: 0.9640808, 0.9999847, 0.8248901
Lab: 100,, -0,03, 0,02
LCH: 100, 0.04, 154.72°
Yxy: 1, 0.35, 0.36
Luv: 100, 0.21, 0.49
5000°K
It sounds to me like Colorthink is showing the relative colorimetric
white point, not the absolute white point. ICC relative colorimetric
white is defined as being D50, so it's not telling you anything useful.
It makes me think that this is an indication of error, perhaps the
problem you mention with some profiling software outside the target
range. Would this mean that the dynamic range of the scanner exceeds the
expected response by the profiling software for the white patch. Such
that any white patch value measured above L*88 would be shot to L*100
and the profile cannot process values between the two?
You would hope that any useful scanner will have a greater dynamic
range than any media you place on it, and since it is physically
impossible to have a 100% reflective diffuse surface, while it
is perfectly possible to calibrate the scanner to register such
a surface (and many may be so calibrated to register this as 255),
it is usual that the test chart white patch will scan with a value
less than 255.
So if you feed values greater than the test chart white device
value into the profile, the output is undefined as far as the
profile is concerned, and it's up to the profiling software
as to what to do with it. The profile can't contain
L* values above 100, so it can't extrapolate in that direction.
Whether this has anything to do with your profile, only you
can tell.
Graeme Gill.
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