// using System.Runtime.InteropServices;

        [DllImport("gdi32.dll")]
        protected static extern int GetDeviceCaps(int hDC, int nIndex);
        [DllImport("user32.dll")]
        protected static extern int GetDC(int hwnd);
        [DllImport("user32.dll")]
        protected static extern int ReleaseDC(int hwnd, int hDC);

        static void Farbtiefe()
        {
            int hDC = GetDC(0);
            int Pixels = GetDeviceCaps(hDC, 12);
            int x = ReleaseDC(0, hDC);

            string rlt = "";
            switch (Pixels)
            {
                case 1: rlt = "Monochrom"; break;
                case 4: rlt = "16 Farben"; break;
                case 8: rlt = "256 Farben"; break;
                case 16: rlt = "HighColor (16 Bit)"; break;
                case 32: rlt = "TrueColor (32 Bit)"; break;
            }
       }