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POConvert RGB to YCbCr - C code
 

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  1. POConvert RGB to YCbCr - C code
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    <p>I need to convert RGB to YCbCr for my final project and I trying to do this way (I'm programming in C):</p> <pre><code>/* Autor: Vinicius Garcia * Data : 09.ago.2011 * * Função que converte um pixel RGB em YCbCr * * param : int R valor do pixel no canal red * param : int G valor do pixel no canal green * param : int B valor do pixel no canal blue * return: int* vetor de inteiros com os valores H, S e V calculados - nesta ordem */ int* converter_RGB_para_YCbCr(int R, int G, int B){ int* YCbCr = (int*) malloc(3 * sizeof(int)); double delta = 128.0; //Constante necessaria para o calculo da conversão de cor double Y = (0.299 * R + 0.587 * G + 0.114 * B); double Cb = ((B - Y) * 0.564 + delta); double Cr = ((R - Y) * 0.713 + delta); YCbCr[0] = (int) Y; YCbCr[1] = (int) Cb; YCbCr[2] = (int) Cr; return YCbCr; } </code></pre> <p>But it doesn't work for me!</p> <p>I was comparing with cvCvtColor (from OpenCv library) and the results doesn't match:</p> <pre><code> R = 88, G = 76, B = 78 cvCvtColor: Y = 80, Cb = 127, Cr = 134 myfunction: Y = 382, Cb = 132, Cr = 132 (cr and cr are always equal!) </code></pre> <p>I really need help with this, I trying do this for a long time and I couldn't find any answer for my doubt.</p> <hr> <p>Do you guys think I'm getting the RGB values wrong? I'm doing this way:</p> <pre><code>uchar B = CV_IMAGE_ELEM(img_RGB, uchar, linha, coluna * 3); uchar G = CV_IMAGE_ELEM(img_RGB, uchar, linha, coluna * 3 + 1); uchar R = CV_IMAGE_ELEM(img_RGB, uchar, linha, coluna * 3 + 2); </code></pre> <p>Then I'm calling my conversion function this way:</p> <pre><code>converter_RGB_para_YCbCr(R, G, B); </code></pre> <p>My function expects int R, int G, int B but I'm passing uchar B, uchar G, uchar R. its that ok?</p>
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    1. USVinicius Garcia
    1. USVinicius Garcia
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    1. COHmm, that is Odd; even doing it by hand and using your method, Y = 80 (or rather rounded to 80 when converted to int) Can you inspect your method at the point where you assign Y,Cb and Cr to your YCbCr return value, and post what the values are here ?
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      1. POConvert RGB to YCbCr - C code
      1. USRuss Clarke
    2. COAlso what is this delta for ? I've not seen that used myself. Ill post an answer with the conversion as I'm aware of it...
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      1. POConvert RGB to YCbCr - C code
      1. USRuss Clarke
    3. CONo idea where you get Y = 382, it can never be > 255, assuming that R, G and B can be maximum 255. I get Y = 79.816, using a "pocket" calculator.
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      1. POConvert RGB to YCbCr - C code
      1. USRudy Velthuis
 

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