[argyllcms] Re: profile function and no and ni tags
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sat, 01 Sep 2007 20:14:45 +1000
John Weissberg wrote:
I have made a printer profile using the following command:
profile -ni -no -qm -bh mydata.ti3
Even though I specified the -ni and -no tags, when I do iccdump of
either AtoB or BtoA tags I certainly do see the input and output
matrices in addition to the CLUT.
For ICC V2 the lut input and output curves are not optional,
they have to be present. They can only be set to an identity
transfer.
The first few values of the BtoA1 input matrix are below. The values are
clearly not the identity matrix. How can I force both the input matrix
and output matrix to be the identity matrix?
You don't want this. The B2A input curves with -ni -no have no data
dependent nature, but the a* and b* curves are offset to ensure that
the a*=b*=0 input value lands exactly on a clut grid point. This is due
to the asymmetric nature of ICC L*a*b* PCS encoding. If this weren't
the case, white wouldn't map to perfect device white.
Graeme Gill.
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