Re: [Lcms-user] Unscaled XYZ profile creation measurement data

[Hal V. E. <hv...@as...>]

On Thursday 10 January 2008 00:55:48 Michael A. Litscher wrote:
> Hello all,
>
> Does anyone know what lcms functions to call to get the unscaled XYZ
> measurement data from a monitor's profile for the RGB(0, 0, 0) and RGB(255,
> 255, 255) swatches used during the profile's creation?  Also, would it be
> safe to assume that the measurement data for these two swatches exists in
> every monitor profile created using industrial grade profiling software?  I
> would like to use this data to shift and scale any further measurements of
> the monitor from XYZ(0, 0, 0) to XYZ(monitor's white point) without having
> to re-display and re-read RGB(0, 0, 0) and RGB(255, 255, 255) swatches.  It
> would also allow me to measure any shifts in luminance and chromaticity
> since the profile's creation.  The cmsTakeCharTargetData function seems the
> most likely, but the documentation for this function states that the tag
> this data is stored under is optional.

This tag is optional and I suspect that most profiles will not have this data.  
Some profilers like LProf will include this data but only if users select the 
highest verbosity level when creating the profile.  Most commercial profilers 
do not allow users to specify which optional tags to include in the profile 
so it is unlikely that profiles created by these will have this data.  But 
the only way to know is to check profiles created with different (or with 
your) profilers.

If the data is included it will be in a form that in most cases will look like 
a CGATS measurement file and you will likely not find anything clearly marked 
as a white or black point (this is the case for LProf).  You will have to 
parse through the data to find which measurements correspond to the white and 
black points.  In addition the exact format of the data will likely vary 
depending on the profiler used to create the profile.  For example LProf will 
show the RGB values of the patches in the range of 0 to 255 but ArgyllCMS 
will have 0 to 100 for these.  Other profilers may be different if the data 
is present at all.  One other thing to keep in mind is that some profilers 
will measure several white point patches during the profiling process in 
order to reduce measurement noise for the white point so you may find more 
than one white point measurement  (IE. patches where R=G=B=max RGB value) in 
this tag data.

>
> If this data isn't available, how do I get the absolute luminance XYZ
> value?  The function cmsIsTag returns true for icSigLuminanceTag, but none
> of the exported cmsTake functions seem to capable of returning an XYZ
> structure or just Y for icSigLuminanceTag.  The ReadICCXYZ function looks
> capable, but it isn't exported.
>
> Thank you for your time,
>
> Michael A. Litscher
> CTO, ColorMetrix Technologies, LLC
>
>
> -------------------------------------------------------------------------
> Check out the new SourceForge.net Marketplace.
> It's the best place to buy or sell services for
> just about anything Open Source.
> http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplac
>e _______________________________________________
> Lcms-user mailing list
> Lcm...@li...
> https://lists.sourceforge.net/lists/listinfo/lcms-user