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POWhy are pixel values of an image different between reading methods?
 

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  1. POWhy are pixel values of an image different between reading methods?
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    <p>This puzzles me for last two hours. Reading an image file results in different pixel values between imread in Matlab and Image.FromFile in C#?</p> <pre><code>aa=imread('myfile.tif') max(aa(:)) = 248 in matlab </code></pre> <p>In C#</p> <pre><code>var image2Array = imageToByteArray((Bitmap) Image.FromFile("myfile.tif")); byte maxx = 0; foreach(var a in image2Array) { maxx = Math.Max(maxx, a); } //maxx = 255 </code></pre> <p>Futhermore, in Matlab, </p> <pre><code>aa(1,1) = 13, aa(1,2) = 13 </code></pre> <p>but in C#</p> <pre><code>image2Array[0]=17, image2Array[1]=0 </code></pre> <p>They should be the same.</p> <p>BTW, in this case, pixel type is uint8. so there is no dimensional difference. </p> <p>If you ask me how I got byte array from Image, I used <a href="http://msdn.microsoft.com/en-us/library/5ey6h79d%28v=vs.80%29.aspx" rel="nofollow">MSDN document</a> to make this method.</p> <pre><code> public byte[] imageToByteArray(Bitmap bmp) { // Lock the bitmap's bits. Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height); BitmapData bmpData = bmp.LockBits( rect, 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. int bytes = Math.Abs(bmpData.Stride)*bmp.Height; byte[] rgbValues = new byte[bytes]; // Copy the RGB values into the array. System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes); // Unlock the bits. bmp.UnlockBits(bmpData); return rgbValues; } </code></pre> <p>What did I do wrong here? I suspect that they use different reading algorithms because two resulting images look same.</p> <p><strong>UPDATE:</strong></p> <p>I don't think there is anything wrong with what I was doing. I concluded that reading tif as a bitmap was the cause of the problem. To confirm this theory, </p> <ol> <li><p>I displayed the two images and they looked exactly the same. So there is no mistake on my part, I think.</p></li> <li><p>I tried to read the same file with opencv and its pixel values were exactly the same as the ones from matlab. This was surprisingly to me. I would very cautiously use Bitmap in C# from now on.</p></li> </ol>
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