[argyllcms] Re: gamut conversion through the LUT ?!
- From: "Hal V. Engel" <hvengel@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 21 Jul 2008 15:02:32 -0700
On Monday 21 July 2008 02:45:58 pm lee scratchy wrote:
> humm OK makes sense and would explain our results :(
>
> so even an ICC v4 can't help ?
>
> I read that there is 3x3 matrixes in the v4 ICC specs ?
>
> http://www.color.org/createv4.pdf
>
> sRGB gamut after color re-rendering by the new v4 ICC profile (transparent
> green) ... 3D CLUT = 3x3 matrix XYZ(D50) to RGB linear ...
>
> any idea how could I create such an ICC file ? :)
>
> Thanks,
>
> -Maxime
I think you are confused. Video card LUTs are 1D but the LUTs in ICC profiles
are 3D (or more). With 1D LUTs gamut mapping is not possible since the most
you can do with 1D LUTs is correct the gamma and neutral point of the device.
The 1D LUT does not have enough information to correct for anything beyond
this. With 3D LUTs you can do things like gamut mapping and other colorspace
conversions.
It is possible to use a gl shader program to do 3D LUT color space
conversions. But this does NOT use the video cards hardware LUTs but instead
uses LUTs stored in the video cards general memory space. There is an OpenICC
Google Summer of Code project that is working on adding GPU driven color space
conversion to enable system wide CM on X11 systems. I believe that this
project has had gl shaders doing 3D LUT color space conversions for some time
now.
>
> > Date: Mon, 21 Jul 2008 23:35:31 +0200
> > From: nospam456@xxxxxx
> > To: argyllcms@xxxxxxxxxxxxx
> > Subject: [argyllcms] Re: gamut conversion through the LUT ?!
> >
> > lee scratchy wrote:
> >> what the Pixel Shader script does is a simple 3D matrix from what I
> >> understand :
> >> [...]
> >> so are you saying that this can't be done through the LUT ?
> >
> > Yes, a 3D matrix multiplication can't be done with one-dimensional LUTs.
> > As I said, you need a three-dimensional LUT to accomplish what you want.
> > But the VCGT in the graphics card is just a one-dimensional LUT :-(
> >
> > Regards,
> > Gerhard
>
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