[argyllcms] Re: XYZ/LAB to RGB
- From: Gerhard Fuernkranz <nospam456@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 08 Jan 2010 18:54:25 +0100
Pascal de Bruijn wrote:
> On Fri, Jan 8, 2010 at 12:12 AM, Klaus Karcher <lists@xxxxxxxxxxxxxxxxx>
> wrote:
>
>> Pascal de Bruijn wrote:
>>
>>> Hi,
>>>
>>> Argyll uses RGB values in it's ti2 files for printer profiling:
>>>
>>> SAMPLE_ID SAMPLE_LOC RGB_R RGB_G RGB_B XYZ_X XYZ_Y XYZ_Z
>>> 29 "B12" 22.745 18.431 73.333 12.622 7.4458 48.192
>>>
>>> Say I have some XYZ or LAB values, how can I compute the proper RGB
>>> values?
>>>
>> the XYZ values in ti2 files are estimated and only intended for validation
>> purposes. Why do you want to transform them to RGB?
>>
>> see
>> <file:///Applications/argyll/Argyll_V1.1.0_RC1/doc/File_Formats.html#.ti2>
>>
>>
>>> And is there an easy way to do this for larger data sets?
>>>
>> you can use icclu, xicclu or fakeread to transform colors from/to different
>> colorspaces.
>>
>
> Well, that's more or less my question in what colorspace are the RGB
> values in a ti2 file? sRGB?
>
> Basically I'd like to be able to add these patches to a printer target:
> http://www.oyranos.org/wiki/images/a/aa/ColorChecker_vendor_D50_2deg.cie
>
> This file has XYZ/LAB data, but not RGB, which printtarg seems to
> need, since setting the RGB to 0-0-0 produces black patches.
>
But a printer calibration target is supposed to prescribe the _device_
numbers (i.e. RGB or CMYK,...), while CIE numbers will be measured after
printing the target.
If you want to add particular CIE colors to your chart, then you already
need a (preliminary) profile for you printer and use this profile to
convert from XYZ/CIELAB to RGB.
Regards,
Gerhard
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