Re: [Lcms-user] Apply profile with PCS = cmsSigXYZData, Color Space = cmsSigGrayData

[Martí M. <mar...@li...>]

Hi,

 >Thanks, Marti. Is the white point and transfer function not already 
specified in the profile? Pardon my ignorance,
 >not that familiar with colour transforms.


No worries, if you use a real profile, yes, it is included in the 
profile. If you use a built-in profile, that is a template to generate 
profiles, so you need parameters.

Try this:

// A gamma-2.2 gray space
static
cmsHPROFILE Create_Gray22(void)
{
     cmsHPROFILE hProfile;
     cmsToneCurve* Curve = cmsBuildGamma(DbgThread(), 2.2);
     if (Curve == NULL) return NULL;

     hProfile = cmsCreateGrayProfileTHR(DbgThread(), cmsD50_xyY(), Curve);
     cmsFreeToneCurve(Curve);

     return hProfile;
}

Regards

Marti


On 20/02/2017 17:33, Aaron Boxer wrote:
> Thanks, Marti. Is the white point and transfer function not already 
> specified in the profile? Pardon my ignorance,
> not that familiar with colour transforms.
>
> On Mon, Feb 20, 2017 at 11:28 AM, Martí Maria 
> <mar...@li... <mailto:mar...@li...>> wrote:
>
>
>     Hi,
>
>     You need to specify white point and transfer function to
>     cmsCreateGrayProfile(), see manual page 28
>
>     Regards
>
>     Marti
>
>     On 20/02/2017 7:04, Aaron Boxer wrote:
>>     Hello,
>>
>>     I have a jpeg 2000 file with an ICC profile.
>>
>>     PCS is cmsSigXYZData and color space is cmsSigGrayData.
>>
>>     The file can be found here:
>>     https://github.com/GrokImageCompression/grok/issues/38
>>     <https://github.com/GrokImageCompression/grok/issues/38>
>>
>>     I am working on a library that decodes the jpeg 2000 file and
>>     applies the ICC profile, using LCMS.
>>
>>     Currently, I have this code:
>>
>>      in_type = TYPE_GRAY_8;
>>      out_type = TYPE_RGB_8;
>>      out_prof = cmsCreate_sRGBProfile();
>>
>>     and I can create the transform and apply the ICC profile, but the
>>     output is an RGB file.
>>     What I would like is to output a grayscale file.
>>
>>     So, if I instead call
>>
>>     out_prof = cmsCreateGrayProfile(NULL,NULL);
>>
>>     then cmsCreateTransform  returns NULL and I can't apply the profile.
>>
>>
>>     What is the best way of creating a transform for this kind of
>>     grayscale image ?
>>
>>     Thanks so much,
>>     Aaron
>>
>>
>>
>>
>>
>>
>>
>>
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