图片增添高斯噪声

图片添加高斯噪声
 这是添加高斯噪声的代码，有没有大神看看为什么这个代码只能给部分图像加噪声
private void btngauss_Click(object sender, EventArgs e)
        {
            if (CurBitmap != null)
            {
                gaussnoise gnoise = new gaussnoise();
                if (gnoise.ShowDialog() == DialogResult.OK)
                {

                    Rectangle rect = new Rectangle(0, 0, CurBitmap.Width, CurBitmap.Height);
                    System.Drawing.Imaging.BitmapData bmpData = CurBitmap.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, CurBitmap.PixelFormat);
                    IntPtr ptr = bmpData.Scan0;
                    int bytes = CurBitmap.Width * CurBitmap.Height;
                    byte[] grayvalues = new byte[bytes];
                    System.Runtime.InteropServices.Marshal.Copy(ptr, grayvalues, 0, bytes);
                    double temp = 0;
                    Random r1, r2;
                    double v1, v2;
                    r1 = new Random(unchecked((int)DateTime.Now.Ticks));
                    r2 = new Random(unchecked((int)DateTime.Now.Ticks));
                    for (int i = 0; i < bytes; i++)
                    {
                        do
                        {
                            v1 = r1.NextDouble();
                        }
                        while (v1 <= 0.00000000001);

                        v2 = r2.NextDouble();
                        temp = Math.Sqrt(-2 * Math.Log(v1)) * Math.Cos(2 * Math.PI * v2) * gnoise.GetSigma + gnoise.GetMean;
                        //temp = (1 / gnoise.GetSigma * Math.Sqrt(2 * Math.Sqrt(2 * Math.PI)) * Math.Pow(Math.E, - (Math.Pow(v1 - gnoise.GetMean, 2) / (2 * gnoise.GetSigma * gnoise.GetSigma))));
                        temp = temp + grayvalues[i];
                        if (temp > 255)
                        {
                            grayvalues[i] = 255;

                        }
                        else if (temp < 0)
                        {
                            grayvalues[i] = 0;
                        }
                        else
                            grayvalues[i] = Convert.ToByte(temp);
                    }
                    System.Runtime.InteropServices.Marshal.Copy(grayvalues, 0, ptr, bytes);
                    CurBitmap.UnlockBits(bmpData);
                }
                gnoise.Close();
                Invalidate();
            }

[解决办法]
int bytes = CurBitmap.Width * CurBitmap.Height;
长度不对，标准一个像素点包含RGB三个字节，所以应该是

int bytes = CurBitmap.Width * CurBitmap.Height*3;