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    <p>The performance issue is caused by GetPixels/SetPixels, which is an extraordinarily slow way to access the data in an .NET Bitmap. Instead, I would look into the Bitmap.LockBits method to get a pointer to the bitmap and manipulate data directly. It will be an order of magnitude faster. </p> <p>See <a href="http://msdn.microsoft.com/en-us/library/5ey6h79d%28v=vs.80%29.aspx">MSDN</a>: </p> <blockquote> <p>The following code example demonstrates how to use the PixelFormat, Height, Width, and Scan0 properties; the LockBits and UnlockBits methods; and the ImageLockMode enumeration. This example is designed to be used with Windows Forms. To run this example, paste it into a form and handle the form's Paint event by calling the LockUnlockBitsExample method, passing e as PaintEventArgs.</p> </blockquote> <pre><code>private void LockUnlockBitsExample(PaintEventArgs e) { // Create a new bitmap. Bitmap bmp = new Bitmap("c:\\fakePhoto.jpg"); // Lock the bitmap's bits. Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height); System.Drawing.Imaging.BitmapData bmpData = bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, bmp.PixelFormat); // Get the address of the first line. IntPtr ptr = bmpData.Scan0; // Declare an array to hold the bytes of the bitmap. // This code is specific to a bitmap with 24 bits per pixels. int bytes = bmp.Width * bmp.Height * 3; byte[] rgbValues = new byte[bytes]; // Copy the RGB values into the array. System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes); // Set every red value to 255. for (int counter = 2; counter &lt; rgbValues.Length; counter+=3) rgbValues[counter] = 255; // Copy the RGB values back to the bitmap System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, bytes); // Unlock the bits. bmp.UnlockBits(bmpData); // Draw the modified image. e.Graphics.DrawImage(bmp, 0, 150); } </code></pre> <p>If you want to go even faster rather than copy the array out, manipulate it and copy it back, you can operate on the bitmap in place using an unsafe pointer. In this case, the inner part would change as follows:</p> <pre><code> // Lock the bitmap's bits. Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height); System.Drawing.Imaging.BitmapData bmpData = bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, bmp.PixelFormat); // Get the address of the first line. IntPtr ptr = bmpData.Scan0; // Declare an array to hold the bytes of the bitmap. // This code is specific to a bitmap with 24 bits per pixels. int bytes = bmp.Width * bmp.Height * 3; unsafe { byte* rgbValues = (byte*)ptr; // Set every red value to 255. for (int counter = 2; counter &lt; bytes counter+=3) rgbValues[counter] = 255; } // Unlock the bits. bmp.UnlockBits(bmpData); </code></pre> <p>Just take care to note the PixelFormat of the bitmap. The example above assumes its 24 bits per pixel BGR. In actual fact many bitmaps are BGRA (32bits per pixel) so you will need to modify four bytes for Blue, Gree, Red, Alpha in that order per pixel. </p>
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    1. POc# Low performance in for-loop while searching pixels in image
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    1. COI can't really agree cause i'm also iterating over a bitmap with LINQ and call GetPixel()/SetPixel() without any noticeable performance hits. So i think it's maybe good to know this approach but i think the users problems is the slow `catch{}` clause like Steven wrote in his comment.
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    2. CO@Oliver the catch{} clause will only cause a performance problem if you are throwing exceptions. If that is the case then yes I would agree. An catch{} that is never used is not going to make a difference! I'd add some logging to the catch and try to see how often its throwing.
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    3. CONormally it does not use the catch{}, only if it for some reason detects an image too close to the border of the image, which shouldn't happen. I also tried removing the catch{} with no result.
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