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  1. PO
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    <p>Without understanding your measurement of greenness, the lines which computes the measurement is:</p> <pre><code>nCombinedVal = (pixelPtr[nPixelPos +2]) *( 255 - pixelPtr[nPixelPos +1]); </code></pre> <p>The nPixelPos is the index to the pixel. If the image follows the OpenCV BGR convention +1 will give you the green channel and +2 gives you the red channel. If it follows the RGB convention, +1 will still be green but +2 will be blue.</p> <p><strike>To change detected color to red, my best guess would be to replace +1 with +2 and change +2 to +1 or +0. Be sure to modify both lines.</p> <pre><code>nCombinedVal = (pixelPtr[nPixelPos +1]) *( 255 - pixelPtr[nPixelPos +2]); </code></pre> <p></strike></p> <p>If you would be willing to replace the code, I would suggest a different measurement of color:</p> <pre><code>greenness = green - max(red, blue) redness = red - max(green, blue) blueness = blue - max(red, green) </code></pre> <p><strike> Which would look something like this in your code:</p> <pre><code>for(int i = 0; i &lt; img_output.rows; i++) { for(int j = 0; j &lt; img_output.cols; j++) { nPixelPos = i*img_output.cols*cn + j*cn; int greenness = int(pixelPtr[nPixelPos +1]) - max(pixelPtr[nPixelPos], pixelPtr[nPixelPos +2]); if (greeness &gt; 10) { pixelPtr1[nPixelPos + 0] = 255; pixelPtr1[nPixelPos + 1] = 255; pixelPtr1[nPixelPos + 2] = 255; } else { pixelPtr1[nPixelPos + 0] = 0; pixelPtr1[nPixelPos + 1] = 0; pixelPtr1[nPixelPos + 2] = 0; } } } </code></pre> <p></strike></p> <p><strong>EDIT:</strong> OpenCV stores HSV color information in reversed order and divides hue by two to fit into a byte (more details <a href="http://docs.opencv.org/modules/imgproc/doc/miscellaneous_transformations.html?highlight=cvtcolor#cvtcolor" rel="nofollow">here</a>). pixelPtr[nPixelPos +2] is therefore the hue and pixelPtr[nPixelPos +1] is the saturation. To change the color you are looking for, replace the row with something like this:</p> <pre><code>nCombinedVal = abs(pixelPtr[nPixelPos +2]-target_hue) *( 255 - pixelPtr[nPixelPos +1]); </code></pre> <p>Where target_hue is the hue you want to find divided by two.</p>
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    1. POColor detection in openCV - Pixel checking issue
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    1. USmorotspaj
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    1. POColor detection in openCV - Pixel checking issue
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    1. COHI Can you please tell me the OpenCV HSV convention ? As I am using HSV to find colour here .
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      1. USJean-Luc Godard
    2. COHSV information is now added!
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