How to access each byte in a bitmap image

Question

Say I have a bitmap image, is it possible to iterate through all the individual bytes in the image? If yes, how?

Answer 1

Use LockBits member on Bitmap class to obtain BitmapData, then use Scan0 and Marshal.ReadByte to readbytes. Here is small example (it is not about correct brightness adjustment, though):

    public static void AdjustBrightness(Bitmap image, int brightness)
    {
        int offset = 0;
        brightness = (brightness * 255) / 100;
        // GDI+ still lies to us - the return format is BGR, NOT RGB.
        BitmapData bmData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

        int stride = bmData.Stride;
        IntPtr Scan0 = bmData.Scan0;

        int nVal = 0;
        int nOffset = stride - image.Width * 3;
        int nWidth = image.Width * 3;

        for (int y = 0; y < image.Height; ++y)
        {
            for (int x = 0; x < nWidth; ++x)
            {
                nVal = Marshal.ReadByte(Scan0, offset) + brightness;

                if (nVal < 0)
                    nVal = 0;
                if (nVal > 255)
                    nVal = 255;

                Marshal.WriteByte(Scan0, offset, (byte)nVal);
                ++offset;
            }
            offset += nOffset;
        }
        image.UnlockBits(bmData);
    }