[argyllcms] Re: CC Profiles In X Specification and dispwin

On Sunday 13 January 2008 04:28:42 Alastair M. Robinson wrote:
> xcalib's loading of calibration data into the LUTs works exactly
> the same way as xgamma - except that the data taken from the calibration
> portion of the ICC profile is calculated specifically to bring the
> display as close to an "ideal" state as possible.

Sort of.  Programs like xgamma and monica actually make a different call to 
the xserver than programs like dispwin and xcalib.  There are actually two 
sets of calls that can be used to set the video card LUT (this is also true 
on Windows and OS/X).  One is a very simple call that is passed an offset 
from the default curve and the xserver uses this offset to calculate the new 
gamma curves.  The offset can be either positive or negative.  In this case 
the LUT curve is always smooth and always deflected the same direction from 
the default curve (IE. it does not cross over the default curve).  This is 
what xgamma and monica uses.  

Applications like xcalib and dispwin use a more complex API that is actually 
passed a complete copy of the new version of the video card LUT.  This allows 
for the LUT curves to have arbitrary shapes even to the point of having 
discontinuities and/or reversals in the curves (this should be avoided but 
the xserver does not check for this).  For example it is possible this way to 
have parts of the new curve be both above and below the default linear curve 
and this is not possible with the API that is used by xgamma.

Hal

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