GSoC CM collaboration
madman2003 at gmail.com
Sun Mar 2 12:01:45 PST 2008
On 3/2/08, Hal V. Engel <hvengel at astound.net> wrote:
> On Sunday 02 March 2008 11:28:39 Maarten Maathuis wrote:
> > On 3/2/08, Kai-Uwe Behrmann <ku.b at gmx.de> wrote:
> > > Am 02.03.08, 19:56 +0100 schrieb Maarten Maathuis:
> > > > On 3/2/08, Kai-Uwe Behrmann <ku.b at gmx.de> wrote:
> > > > > Am 02.03.08, 19:14 +0100 schrieb Maarten Maathuis:
> > > > > > What kind of color correction do you have in mind? (besides the
> > > > > > usual gamma adjustment)
> > > > >
> > > > > Many colour transformations are CLUT based. This is in case of X a
> > > > > 3 dimensional table to interpolate from input to output. Additional
> > > > > gamma and matix operations can play a role. But for LCD's more and
> > > > > more CLUT's are used, as these devices are sometimes very non linear
> > > > > other than CRT's.
> > > >
> > > > If all you want is control of the LUT's, then i suggest you look at
> > > >
> > > > randrproto. I'm not sure if it's perfect yet, but it should be
> > > > reasonable.
> > >
> > > You talk about the graphics card gamma tables, while I talk about 3
> > > dimensional tables. Usually the a 3*3*17 sized for monitors and
> > > additional one dimensional curves.
> > > A 3*3*17 cube needs some interpolation routine to get the final
> > > output from an argitrary input. A nearest match would not suffice.
> > Why 3d tables if i may ask?
> Because it is a 3D problem. For output devices like monitors color management
> maps from some absolute color space such as CIELab or CIEXYZ into the devices
> color space in a way that corrects all colors not just those along the
> neutral axis. The most you can do with the video card LUT is to get the per
> channel gamma to be well behaved and the R=G=B axis to be close to neutral.
> You can not get colors correct for R!=G!=B. This is a direct result of the
> 1D limitation of the video card LUTs.
> An example, where this becomes very apparent is with the newer LED based wide
> gamut monitors. Even with a well calibrated video card LUT the display
> colors where R!=G!=B, with out full color management, will be much too
> saturated to the point of being garish. These monitors are starting to
> become fairly common so this will only become more of an issue going forward.
You're essentially assuming that the individual color channels are not
> > > The graphics card gamma tables are one dimensional, containing usual
> > > 3*256 values.
> > True.
> > > kind regards
> > > Kai-Uwe Behrmann
> > > --
> > > developing for colour management
> > > www.behrmann.name + www.oyranos.org
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