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    <p>As emgu website state there are primarly two strategies:</p> <p><strong>The safe (slow) way</strong></p> <p>Suppose you are working on an <code>Image&lt;Bgr, Byte&gt;</code>. You can obtain the pixel on the y-th row and x-th column by calling</p> <pre><code>Bgr color = img[y, x]; </code></pre> <p>Setting the pixel on the y-th row and x-th column is also simple</p> <pre><code>img[y,x] = color; </code></pre> <p><strong>The fast way</strong></p> <p>The Image pixels values are stored in the Data property, a 3D array. Ok so this is true but does not tell how to do it in a real scenario. So let's see some working code and then discuss performance and optimization:</p> <pre><code>Image&lt;Bgr, Byte&gt; original = newImage&lt;Bgr, byte&gt;(1024, 768); Stopwatch evaluator = newStopwatch(); int repetitions = 20; Bgr color = newBgr(100, 40, 243); evaluator.Start(); for (int run = 0; run &lt; repetitions; run++) { for (int j = 0; j &lt; original.Cols; j++) { for (int i = 0; i &lt; original.Rows; i++) { original[i, j] = color; } } } evaluator.Stop(); Console.WriteLine("Average execution time for {0} iteration \n using column per row access: {1}ms\n", repetitions, evaluator.ElapsedMilliseconds / repetitions); </code></pre> <p>So this is the average running time that you have after 20 runs using the safe slow way of setting image pixel On my machine it takes <strong>1021ms</strong>...</p> <p>So 1021 milliseconds as average time for looping and setting a number of pixels equal to 1024*768. We could have done a little bit better by looping on row by row </p> <p>So let's refactor a little bit our code and let's use the faster way using directly Image.Data property:</p> <pre><code>evaluator.Reset(); evaluator.Start(); for (int run = 0; run &lt; repetitions; run++) { for (int i = 0; i &lt; original.Rows; i++) { for (int j = 0; j &lt; original.Cols; j++) { original.Data[i, j, 0] = 100; original.Data[i, j, 1] = 40; original.Data[i, j, 2] = 243; } } } evaluator.Stop(); Console.WriteLine("Average execution time for {0} iterations \n using Data property: {1}ms\n", repetitions, evaluator.ElapsedMilliseconds / repetitions); </code></pre> <p>On my machine it takes <strong>519ms</strong>. So we have gained a performance boost of 50%. The execution time has been decreased by a factor of two.</p> <p>So looking carefully at the code keeping in mind that we are using C#, we can do a minor change that will drastically boost again our image pixel setting performance... <strong>we should not use c# property inside a loop!!!</strong></p> <pre><code>evaluator.Reset(); evaluator.Start(); byte[,,] data = original.Data; for (int run = repetitions - 1; run &gt;= 0; run--) { for (int i = original.Rows - 1; i &gt;= 0; i--) { for (int j = original.Cols - 1; j &gt;= 0; j--) { data[i, j, 0] = 100; data[i, j, 1] = 40; data[i, j, 2] = 243; } } } evaluator.Stop(); </code></pre> <p>With this latest piece of code you will have a huge performance boost <strong>(73ms)</strong> due to correct use of C# language. </p>
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    1. POIterate over pixels of an image with emgu cv
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    1. USLuca Del Tongo
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    1. COThank you so much for that detailed answer! I didn't know that rule, not to use Properties in a loop. One additional question: What does that mean: "unsafe data property". Unsafe in what manner? What are the risks?
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    2. COThere's nothing unsafe in using data property. The developer need more attention in specifying the correct index to get or set the correct value because Data property it's a 3 dimensional array
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      1. USLuca Del Tongo
    3. COI would appreciate if you could share how long time it takes in the last one (not using property)
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      1. USHayri Uğur Koltuk
 

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