上一次利用了 GetPixel 及 SetPixel，將圖片轉為灰階，雖然可以達成效果但是效能不佳！

這次採用 BitmapData 並且使用 指標 進行處理，達到更高的處理效率。

using System;
using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Windows.Forms;

namespace Test
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string Photo_route = Path.Combine(System.AppDomain.CurrentDomain.SetupInformation.ApplicationBase, "Tulips.jpg");
            Bitmap b = (Bitmap)Bitmap.FromFile(Photo_route);
            pictureBox2.Image = (Bitmap)Bitmap.FromFile(Photo_route);
            Stopwatch sw = new Stopwatch();
            sw.Start();
            BitmapData bData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            //使用unsafe允許使用指標
            unsafe
            {
                byte* p = (byte*)bData.Scan0.ToPointer();
                for (int y = 0; y < b.Height; y++)
                {
                    for (int x = 0; x < b.Width; x++)
                    {
                        byte newColor = (byte)((float)(p[0] + p[1] + p[2]) / 3.0f);
                        p[0] = p[1] = p[2] = newColor; //三個byte組成一個Pixel
                        p += 3;
                    }
                }
                b.UnlockBits(bData);
            }
            sw.Stop();
            pictureBox1.Image = b;
            MessageBox.Show(sw.ElapsedMilliseconds.ToString() + " /ms");
        }
    }
}

unsafe開啟方法：