Question

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#?

aa=imread('myfile.tif')

max(aa(:)) = 248 in matlab

In C#

var image2Array = imageToByteArray((Bitmap) Image.FromFile("myfile.tif"));
byte maxx = 0;
foreach(var a in image2Array)
{
     maxx = Math.Max(maxx, a);
}
//maxx = 255

Futhermore, in Matlab,

aa(1,1) = 13, 
aa(1,2) = 13 

but in C#

image2Array[0]=17,  
image2Array[1]=0

They should be the same.

BTW, in this case, pixel type is uint8. so there is no dimensional difference.

If you ask me how I got byte array from Image, I used MSDN document to make this method.

    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;
    }

What did I do wrong here? I suspect that they use different reading algorithms because two resulting images look same.

UPDATE:

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,

1. I displayed the two images and they looked exactly the same. So there is no mistake on my part, I think.

2. 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.

Answer 1

TIFF has many formats, you are attempting to read it as a bitmap.

I suggest reading it using a proprietary TIFF reader instead : Good Tiff library for .NET