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copied!<p>Here's a copy/pastable version of the function I've come up w/ based on on this thread.</p> <p>The unsafe code expects the bitmap to be Format24bppRgb, and if it's not, it'll convert the bitmap to that format and operate on the cloned version.</p> <p>Note that the call to image.Clone() will throw if you pass in a bitmap using an indexed pixel format, such as Format4bppIndexed.</p> <p>Takes ~200ms to get a histogram from an image 9100x2048 on my dev machine.</p> <pre><code> private long[] GetHistogram(Bitmap image) { var histogram = new long[256]; bool imageWasCloned = false; if (image.PixelFormat != PixelFormat.Format24bppRgb) { //the unsafe code expects Format24bppRgb, so convert the image... image = image.Clone(new Rectangle(0, 0, image.Width, image.Height), PixelFormat.Format24bppRgb); imageWasCloned = true; } BitmapData bmd = null; try { bmd = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb); const int pixelSize = 3; //pixels are 3 bytes each w/ Format24bppRgb //For info on locking the bitmap bits and finding the //pixels using unsafe code, see http://www.bobpowell.net/lockingbits.htm int height = bmd.Height; int width = bmd.Width; int rowPadding = bmd.Stride - (width * pixelSize); unsafe { byte* pixelPtr = (byte*)bmd.Scan0;//starts on the first row for (int y = 0; y < height; ++y) { for (int x = 0; x < width; ++x) { histogram[(pixelPtr[0] + pixelPtr[1] + pixelPtr[2]) / 3]++; pixelPtr += pixelSize;//advance to next pixel in the row } pixelPtr += rowPadding;//advance ptr to the next pixel row by skipping the padding @ the end of each row. } } } finally { if (bmd != null) image.UnlockBits(bmd); if (imageWasCloned) image.Dispose(); } return histogram; } </code></pre>

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