Bitmap to byte[] using Fopen

Question

I am trying to write a code that extracts pixel color values for each pixel in a bitmap file. For such purpose I have imported the bmp as a bitmap object and I have used Bitmap.GetPixel(x,y) method but it was not fast enough for my application. One of my colleagues gave me an advice; I think I can use fopen to open the file itself, parse the byte data to an array. Do any of you have any idea? Using fopen method is not a must, I can use anything.

Thanks in advance.

It's not that easy. You need to convert different formats to your target format from raw data and that's not an easy job. At least this is how much I know. You can use `byte[] data = System.IO.File.ReadAllBytes('file.bmp')` to get your data, but I have spoken about formatting. — MahanGM, Aug 02 '13 at 09:22
The fopen() function isn't any faster or different from FileStream or File.ReadAllBytes() or Image.FromFile(). Focus on using unsafe pointers, *that's* the alternative for GetPixel(). Use Bitmap.LockBits(), there are a ton of google hits out there. — Hans Passant, Aug 02 '13 at 12:01

score 2 · Accepted Answer · answered Aug 02 '13 at 09:39

2

You can use either unsafe code block or you can utilize the Marshal class. I'd solve this way:

public static byte[] GetBytesWithMarshaling(Bitmap bitmap)
{
    int height = bitmap.Height;
    int width = bitmap.Width;

    //PixelFormat.Format24bppRgb => B|G|R => 3 x 1 byte
    //Lock the image
    BitmapData bmpData = bitmap.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
    // 3 bytes per pixel
    int numberOfBytes = width * height * 3;
    byte[] imageBytes = new byte[numberOfBytes];

    //Get the pointer to the first scan line
    IntPtr sourcePtr = bmpData.Scan0;
    Marshal.Copy(sourcePtr, imageBytes, 0, numberOfBytes);

    //Unlock the image
    bitmap.UnlockBits(bmpData);

    return imageBytes;
}

answered Aug 02 '13 at 09:39

Balázs Szántó

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This was the first answer, and it worked perfectly. Thank you. But I was not able to understand what marshal class is about, and what lockbits method does, could you please explain them briefly? – talkanat Aug 02 '13 at 19:24
1

1, Lockbits => During the lifetime of the objects their position in the memory could be changed, for example after a garbage collection. To prevent this behaviour the bitmap is locked/fixed in the memory. I think It works like the fixed statement. 2, Marshal is a static class with bunch of methods to interop between managed and unmanaged code, allocate unmanaged memory, etc. – Balázs Szántó Aug 02 '13 at 20:00

Bitmap to byte[] using Fopen

1 Answers1