Re: [Lcms-user] First steps and some questions

[Andreas R. <a.r...@gm...>]

Thanks a lot for help!

When I convert with Photoshop to sRGB / Absolute Colorimetric, I get different colors than I get from lcms.
Example: At xy(268, 190) I get RGB(0,163,77) in Photoshop, but RGB(77, 164, 1) in lcms.
Both images are opened in Photoshop for picking the colors.

I noticed the color shifts in the border areas, too, but the difference is much bigger there than the difference generated by different positions on the screen.

Code is pretty simple:

QImage* image = new QImage("/Users/ar/Desktop/basICColor_CM-Ampel.jpeg");
    cmsHPROFILE hInProfile, hOutProfile;
    cmsHTRANSFORM hTransform;
    hInProfile  = cmsOpenProfileFromFile("/Users/ar/Desktop/ampel.icc", "r");
    hOutProfile = cmsOpenProfileFromFile("/System/Library/ColorSync/Profiles/sRGB Profile.icc", "r");
    hTransform = cmsCreateTransform(hInProfile,
                                    TYPE_BGR_8,
                                    hOutProfile,
                                    TYPE_BGR_8,
                                    INTENT_ABSOLUTE_COLORIMETRIC, 0);
    cmsCloseProfile(hInProfile);
    cmsCloseProfile(hOutProfile);
    uchar *rgbOutTemp = new uchar[(image->width() * image->height()) * 3];
    uchar *rgbInTemp = new uchar[(image->width() * image->height()) * 3];
    int j = 0;
    for(int y = 0; y < image->height(); y++){
        for(int x = 0; x < image->width(); x++){
            QColor col = image->pixel(x, y);
            rgbInTemp[j] = col.blue();
            rgbInTemp[j + 1] = col.green();
            rgbInTemp[j + 2] = col.red();
            j += 3;
        }
    }
    cmsDoTransform(hTransform,rgbInTemp,rgbOutTemp,image->width()*image->height());
    QImage* imout = new QImage(image->width(), image->height(), QImage::Format_RGB32);
    int s = 0;
    for(int h = 0; h < imout->height(); h++){
        for(int w = 0; w < imout->width(); w++){
            QColor color(rgbOutTemp[s], rgbOutTemp[s+1], rgbOutTemp[s+2]);
            imout->setPixel(w, h, color.rgb());
            s+=3;
        }
    }
    ui->label->setPixmap(QPixmap::fromImage(*imout));
    imout->save("/Users/ar/Desktop/saved.jpg","JPG",100);

Regards
Andreas

Am 27.09.2012 um 20:31 schrieb Marti Maria <mar...@li...>:

> 
> Hi Andreas,
> 
> I have tested your image with PS CS4 and get 1 digital count of deviation of PhotoShop, which is due to the way different CMM do rounding. I can see no differences in color. 
> 
> Could you please detail the steps you follow to get different results?
> 
> Thanks
> Marti.
> 
> 
> El 27/09/2012 19:37, Andreas Rettig escribió:
>> Hello,
>> 
>> I'm trying to make my first steps with LCMS and build a very simple application to get familiar with everything.
>> All I want to do is transform a RGB-Jpeg from a special input profile to sRGB and produce the same results I get when I do exactly the same in Photoshop.
>> 
>> I'm using that image for testing with its embedded ICC profile as Input profile:
>> 
>> http://www.colormanagement.org/download_files/basICColor_CM-Ampel.jpg
>> 
>> Then I do a simple transformation from ampel.icc -> sRGB.icc, with different intents.
>> The results are always a little different from what I can produce in Photoshop (using the same profiles and the same intent).
>> 
>> The traffic light is green after the transformation, which shows me that it roughly works - but I expect to get exactly the same result.
>> 
>> The same happens in Gimp - it's always a little different from what I get through lcms (I saved the results to a file and checked RGB-Values).
>> Especially these grids at the borders have very different colors.
>> 
>> Sourcecode is more or less from the examples, nothing special. Profiles are the exactly the same in lcms and Photoshop.
>> 
>> Regards
>> Andreas
>> 
>> 
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