Convert RGB to Gray Scale without using Pointers

If their implementation is opaque to the compiler too, no code optimization can be done via inlining.

void GrayConversion()
{
    Bitmap BMP = (Bitmap)pictureBox1.Image; // BMP is the source image
    int Width = BMP.Width, Height = BMP.Height;
    Bitmap GRAY = new Bitmap(Width, Height); // GRAY is the resultant image

    // Access the bitmap data
    BitmapData BMPData = BMP.LockBits(new Rectangle(0, 0, Width, Height), 
               ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
    BitmapData GRAYData = GRAY.LockBits(new Rectangle(0, 0, Width, Height), 
               ImageLockMode.WriteOnly, PixelFormat.Format24bppRgb);
 
    // Loop on the rows
    for (int i = 0; i < Height; i++)
    {
        unsafe
        {
            // Start-of-row addresses
            byte* Bmp = (byte*)BMPData.Scan0 + i * BMPData.Stride;
            byte* Gray = (byte*)GRAYData.Scan0 + i * GRAYData.Stride;
 
            // Loop on the pixels
            for (int j = 0; j < Width; j++, Bmp += 3, Gray += 3)
            {
                // Extract the luminance of a source pixel using 14 bits fixed-point
                byte Y = (byte)((4897 * Bmp[2] + 9617 * Bmp[1] + 1868 * Bmp[0]) >> 14);
 
                // Assign it to the corresponding destination pixel
                Gray[2] = Gray[1] = Gray[0] = Y;
            }
        }
    }
 
    // Release
    BMP.UnlockBits(BMPData);
    GRAY.UnlockBits(GRAYData);
 
    picGray.Image = GRAY;
}