[argyllcms] Re: XYZ/LAB to RGB
- From: "Alastair M. Robinson" <profiling@xxxxxxxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 08 Jan 2010 19:20:40 +0000
Hi :)
Pascal de Bruijn wrote:
Well I'd like to try to produce something like a ColorChecker at home.
Getting as near to the real thing as possible.
So I'd like to add the ColorChecker patches during profiling to make
the profile more accurate on those patches.
OK, well all you can do is scatter a few patches roughly where in the
device space you think they'll be. This is precisely *why* I tend to
scatter a few extra near-greys for sparse targets - if I knew the device
values for true greys I wouldn't need to give the profiling process any
help in finding them!
So if I add their RGB values to the profiling patches, and then use
the same RGB values to print the target with the profile, I should get
in the ballpark of a real ColorChecker right?
Remember that RGB values don't mean a lot without a frame of reference -
i.e. an ICC profile - you don't know what the colourchecker patches' RGB
values in the printer's colour space will be until after you've
generated the profile - you can estimate, but that's all.
In the ti1 files targen generates there must be some correlation
between the RGB and XYZ values?
Yes, but it's only a rough generic conversion, because in a .ti2 file
the XYZ values aren't used in any capacity that requires accuracy -
they're only used to allow chartread to spot when the wrong strip's been
read, and print out the "Seem have read strip Y instead of strip X" and
"Unexpected spectral response" warnings.
All the best
--
Alastair M. Robinson
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