[argyllcms] Re: XYZ/LAB to RGB
- From: Pascal de Bruijn <pmjdebruijn@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 8 Jan 2010 19:45:18 +0100
On Fri, Jan 8, 2010 at 6:54 PM, Gerhard Fuernkranz <nospam456@xxxxxx> wrote:
> 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.
Well I'd like to try to produce something like a ColorChecker at home.
Getting as near to the real thing as possible.
So I'd like to add the ColorChecker patches during profiling to make
the profile more accurate on those patches.
So if I add their RGB values to the profiling patches, and then use
the same RGB values to print the target with the profile, I should get
in the ballpark of a real ColorChecker right?
Or am I missing something?
In the ti1 files targen generates there must be some correlation
between the RGB and XYZ values?
Regards,
Pascal de Bruijn
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