Convert CMYK image to RGB image
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Thread: Convert CMYK image to RGB image

  1. #1
    Join Date
    Aug 2004
    Location
    ROMANIA
    Posts
    2

    Convert CMYK image to RGB image

    Hi!

    I'm want to convert a CMYK image to a RGB image using VisualC++6.0 and CMM.

    The code looks like this:

    Input :
    inputPixels - a structure with the pixels from the image
    profile1 - char* the name for the CMYK file profile
    profile2 - char* the name for the RGB file profile

    Output :
    outputPixels- the output pixels


    HPROFILE inputProfile, outputProfile;
    HTRANSFORM transform;
    BOOL result;
    int nPixels = columns * rows;

    inputProfile = OpenColorProfileFromFile(profile1);
    outputProfile = OpenColorProfileFromFile(profile2);

    PHPROFILE pProf = (PHPROFILE)malloc(sizeof(HPROFILE)*2);
    pProf[0] = inputProfile;
    pProf[1] = outputProfile;

    PDWORD intent = (PDWORD)malloc(sizeof(DWORD));
    intent[0] = INTENT_SATURATION;
    transform = CreateMultiProfileTransform(pProf,2, intent,1, BEST_MODE, 2);
    if (transform == NULL)
    {
    ShowError(GetLastError());
    }

    outputPixels = (PixelStruct*)malloc(sizeof(PixelStruct)*nPixels);

    result = TranslateBitmapBits(transform, inputPixels, BM_KYMCQUADS, columns, rows, 0, outputPixels, BM_xBGRQUADS,0,NULL,0);

    if (!result)
    {
    ShowError(GetLastError());
    return NULL;
    }

    return outputPixels;
    }

    This code show the image, but not quite good.
    Those anyone know how to do that.

    P.S. Using the profile1 and profile2 files, in Photoshop the result image is correct.

  2. #2
    Join Date
    Dec 2001
    Location
    Greece, Athens
    Posts
    1,015
    My answer won't be code based, cause I don't know how to directly display a CMYK image. But I know that to convert an CMYK image to RGB values you just do the following


    CMY2RGB:
    --> RED = 1-C
    --> GREEN = 1-M
    --> BLUE = 1-Y ,


    since the RGB ans CMY color spaces are complements. Before doing that though, you have to convert CMYK to CMY by adding the "black" (K) value to the CMY values. The black value is the minimum of the other 3 values:


    CMYK2CMY
    Cyan = minimum(1,Cyan*(1-Black)+Black)
    Magenta = minimum(1,Magenta*(1-Black)+Black)
    Yellow = minimum(1,Yellow*(1-Black)+Black)


    Hope this helps.
    Theodore
    Personal Web Page (some audio segmentation tools): www.di.uoa.gr/~tyiannak

  3. #3
    Join Date
    Dec 2001
    Location
    Greece, Athens
    Posts
    1,015
    I also have found the following link with a demo of such conversion:
    http://www.codeproject.com/tools/xcmyk.asp
    Theodore
    Personal Web Page (some audio segmentation tools): www.di.uoa.gr/~tyiannak

  4. #4
    Join Date
    Apr 2009
    Posts
    4

    Re: Convert CMYK image to RGB image

    Give rgb value
    r=
    g=
    b=
    double R, G, B;
    R = (double) r;
    G = (double) g;
    B = (double) b;

    R = 1.0 - (R / 255.0);
    G = 1.0 - (G / 255.0);
    B = 1.0 - (B / 255.0);

    double C, M, Y, K;
    if (R < G)
    K = R;
    else
    K = G;
    if (B < K)
    K = B;

    C = (R - K)/(1.0 - K);
    M = (G - K)/(1.0 - K);
    Y = (B - K)/(1.0 - K);

    C = (C * 100) + 0.5;
    M = (M * 100) + 0.5;
    Y = (Y * 100) + 0.5;
    K = (K * 100) + 0.5;

  5. #5
    Join Date
    Nov 2008
    Posts
    6

    Re: Convert CMYK image to RGB image

    No he wants to convert the image using ICC profiles color conversion. I have the same problem when I convert from CMYK to RGB. My code is similar to yours. The result is not what I expect. If you find the cause to the problem please post it.

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