Question

I wrote the code below in order to manipulate the color of an image. I want to somehow rip apart each pixel of the image. So for each pixel, i want access to the 5 bits of red, 6 bits of green and 5 bits of blue (as per 16 bit images). How would i change my code to do this? I guess i would have to somehow convert those byte values which i’m setting to bits?

Any help would be great.

        private Bitmap InvertBitmap(Bitmap bmp)
        {

            unsafe
            {
                //create an empty bitmap the same size as original
                Bitmap newBitmap = new Bitmap(bmp.Width, bmp.Height);

            //lock the original bitmap in memory
            System.Drawing.Imaging.BitmapData originalData = bmp.LockBits(
               new Rectangle(0, 0, bmp.Width, bmp.Height),
               System.Drawing.Imaging.ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format24bppRgb);

            //lock the new bitmap in memory
            System.Drawing.Imaging.BitmapData newData = newBitmap.LockBits(
               new Rectangle(0, 0, bmp.Width, bmp.Height),
               System.Drawing.Imaging.ImageLockMode.WriteOnly, System.Drawing.Imaging.PixelFormat.Format24bppRgb);

            //set the number of bytes per pixel
            int pixelSize = 3;

            for (int y = 0; y < bmp.Height; y++)
            {
                //get the data from the original image
                byte* originalImageRow = (byte*)originalData.Scan0 + (y * originalData.Stride);

                //get the data from the new image
                byte* newImageRow = (byte*)newData.Scan0 + (y * newData.Stride);

                for (int x = 0; x < bmp.Width; x++)
                {

                    //set the new image's pixel to the inverted version

                    newImageRow[x * pixelSize] = (byte)(255 - originalImageRow[x * pixelSize + 0]); //B
                    newImageRow[x * pixelSize + 1] = (byte)(255 - originalImageRow[x * pixelSize + 1]); //G
                    newImageRow[x * pixelSize + 2] = (byte)(255 - originalImageRow[x * pixelSize + 2]); //R
                }
            }

            //unlock the bitmaps
            newBitmap.UnlockBits(newData);
            bmp.UnlockBits(originalData);

            return newBitmap;
        }
}

Answer 1

If you have a 16-bit integer x, you can extract ranges of bits within it by first masking those bits with a binary AND, then shifting the result. Like so:

int x = 33808;  // 1000010000010000, for testing

int r = (x & 63488) >> 11;    // 63488 = 1111100000000000
int g = (x & 2016) >> 5;      //  2016 = 0000011111100000
int b = (x & 31);             //    31 = 0000000000011111

// r = 10000
// g = 100000
// b = 10000

I hope that helps.