Bitmap bt = (Bitmap)pictureBox1.Image;
            int width = bt.Width;
            int height = bt.Height;
            for (int i =  0 ; i < width; i++)
                for (int j =  0 ; j < height; j++)
                {
                    Color cl = bt.GetPixel(i, j);

                    int red = cl.R;
                    int green = cl.G;
                    int blue = cl.B;

                    red = (red +  5  <  256 ) ? red +  5  : red;
                    green = (green +  5  <  256 ) ? green +  5  : green;
                    blue = (blue +  5  <  256 ) ? blue +  5  : blue;

                    Color cl2 = Color.FromArgb(red, green, blue);

                    bt.SetPixel(i, j, cl2);
                }
            pictureBox1.Image = bt;