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    <p><code>cv::Mat</code> is preferred over <code>IplImage</code> because it simplifies your code</p> <pre><code>cv::Mat img = cv::imread("lenna.png"); for(int i=0; i&lt;img.rows; i++) for(int j=0; j&lt;img.cols; j++) // You can now access the pixel value with cv::Vec3b std::cout &lt;&lt; img.at&lt;cv::Vec3b&gt;(i,j)[0] &lt;&lt; " " &lt;&lt; img.at&lt;cv::Vec3b&gt;(i,j)[1] &lt;&lt; " " &lt;&lt; img.at&lt;cv::Vec3b&gt;(i,j)[2] &lt;&lt; std::endl; </code></pre> <p>This assumes that you need to use the RGB values together. If you don't, you can uses cv::split to get each channel separately. See etarion's answer for the link with example.</p> <p>Also, in my cases, you simply need the image in gray-scale. Then, you can load the image in grayscale and access it as an array of uchar.</p> <pre><code>cv::Mat img = cv::imread("lenna.png",0); for(int i=0; i&lt;img.rows; i++) for(int j=0; j&lt;img.cols; j++) std::cout &lt;&lt; img.at&lt;uchar&gt;(i,j) &lt;&lt; std::endl; </code></pre> <p><strong>UPDATE</strong>: Using split to get the 3 channels</p> <pre><code>cv::Mat img = cv::imread("lenna.png"); std::vector&lt;cv::Mat&gt; three_channels = cv::split(img); // Now I can access each channel separately for(int i=0; i&lt;img.rows; i++) for(int j=0; j&lt;img.cols; j++) std::cout &lt;&lt; three_channels[0].at&lt;uchar&gt;(i,j) &lt;&lt; " " &lt;&lt; three_channels[1].at&lt;uchar&gt;(i,j) &lt;&lt; " " &lt;&lt; three_channels[2].at&lt;uchar&gt;(i,j) &lt;&lt; std::endl; // Similarly for the other two channels </code></pre> <p>UPDATE: Thanks to entarion for spotting the error I introduced when copying and pasting from the cv::Vec3b example.</p>
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    1. POCycle through pixels with opencv
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    1. USDat Chu
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    1. COHow is it that you get values that are non-integers for the image?
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      1. USDat Chu
    2. CO`img.at<uchar>(i,j)[0]` - this isn't going to work :) the `[0]` has to go
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      1. USetarion
    3. COI got to this question and it solved a problem I had, but now I have the question, why does ::at<uchar> work? why doesnt it work with the at alone? like at(0,0)?
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      1. USZloy Smiertniy
 

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