Encrypt text

public static Image EncryptText(Bitmap img, string text)
		{
            // Size of image :
            int height = img.Height;
            int width = img.Width;

            // Length of string :
            int len = text.Length;

            // Image Response :
            Bitmap response = img;

            // Check if there is the place to incode text
            bool validArguments = (height * width >= len * 1.5 );
            if (validArguments)
            {
                Console.WriteLine("Start encrypt text ...");
                // Create a liste of 4bit Code of string
                int lenBuffer = 2 * len + 2;
                int[] buffer = new int[lenBuffer];

                for (int i = 0; i < len ; i++)
                {
                    buffer[2*i] = text[i] / 16;
                    buffer[2*i + 1] = text[i] % 16;
                }

                // Encode the text in the image
                int itt = 0;
                int selectColor = 0;

                while (itt < lenBuffer)
                {
                    Color oldPixel = img.GetPixel(itt % width, itt / width);
                    int r = oldPixel.R;
                    int g = oldPixel.G;
                    int b = oldPixel.B;

                    if(selectColor == 0)
                    {
                        r = ((oldPixel.R / 16) * 16) + buffer[itt];
                    }
                    else if (selectColor == 1)
                    {
                        g = ((oldPixel.G / 16) * 16) + buffer[itt];
                    }
                    else if (selectColor == 2)
                    {
                        b = ((oldPixel.B / 16) * 16) + buffer[itt];
                    }

                    Color newPixel = Color.FromArgb(oldPixel.A, r, g, b);
                    response.SetPixel(itt % width, itt / width, newPixel);

                    selectColor++;
                    if(selectColor%3 == 0)
                    {
                        selectColor = 0;
                        itt++;
                    }
                }


            }
            Console.WriteLine("Done Encrypt text");
            return response;

        }