Am 17.09.04, 21:02 +0800 schrieb Peter:
> Hello,
>
> I try doing the Lab to CMYK convertion with snippet like below, it works
>
> double fLab[3];
> unsigned char nCMYK[4];
>
> fLab[0] = 50.0;
> fLab[1] = 80.0;
> fLab[2] = 50.0;
> hOutProfile = cmsOpenProfileFromFile(szPath, "r");
> hLabProfile = cmsCreateLabProfile(NULL);
> hTransform = cmsCreateTransform(hLabProfile,
> TYPE_Lab_DBL,
> hOutProfile,
> TYPE_CMYK_8,
> intent, 0);
>
> cmsDoTransform(hTransform, fLab, nCMYK, 1);
> cmsDeleteTransform(hTransform);
> cmsCloseProfile(hLabProfile);
> cmsCloseProfile(hOutProfile);
>
> But when I change it to Lab 8 bit, it does not produce the similar result.
>
> unsigned char nCMYK[4];
> unsigned char nLab[3];
>
> nLab[0] = 50;
> nLab[1] = 80;
> nLab[2] = 50;
> hOutProfile = cmsOpenProfileFromFile(szPath, "r");
> hLabProfile = cmsCreateLabProfile(NULL);
> hTransform = cmsCreateTransform(hLabProfile,
> TYPE_Lab_8,
> hOutProfile,
> TYPE_CMYK_8,
> intent, 0);
>
> cmsDoTransform(hTransform, nLab, nCMYK, 1);
> cmsDeleteTransform(hTransform);
> cmsCloseProfile(hLabProfile);
> cmsCloseProfile(hOutProfile);
>
> Is it because Lab values are different for 8 bit format & double format ?
You can set
nLab[0] = fLab[0] * 255.0 / 100.0;
nLab[1] = fLab[1] + 127.0;
nLab[2] = fLab[2] + 127.0;
> The range is something like this ?
> L = 0 to 100
> a = -127 to 127
> b = -127 to 127
correct
regards
Kai-Uwe Behrmann
+ imaging development / panoramas
+ color management
+ email :[EMAIL PROTECTED]
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