c# winform 把彩色图片转换为灰色的图片,变灰,灰度图片,速度很快,safe,unsafe

把彩色图片转换为灰色的图片,直接用.net接口遍历每个像素点转换的效率非常低,800K的图片65万像素我的电脑要用5分钟,而用了unsafe,速度提高了几千倍,同样的图片只用了0.几秒 

附一个常用的遍历像素点转换的代码 

构造函数 

public Tphc()
{
    InitializeComponent();
    this.pictureBox1.ImageLocation = "F:\黑色头发.jpg";
}

按钮单击事件 

private void button3_Click(object sender, EventArgs e)
{
    int Height = this.pictureBox1.Image.Height;
    int Width = this.pictureBox1.Image.Width;
    Bitmap bitmap = new Bitmap(Width, Height);
    Bitmap MyBitmap = (Bitmap)this.pictureBox1.Image;
    Color pixel;
    for (int x = 0; x < Width; x++)
        for (int y = 0; y < Height; y++)
        {
            pixel = MyBitmap.GetPixel(x, y);
            int r, g, b, Result = 0;
            r = pixel.R;
            g = pixel.G;
            b = pixel.B;
            //实例程序以加权平均值法产生黑白图像
            int iType = 2;
            switch (iType)
            {
                case 0://平均值法
                    Result = ((r + g + b) / 3);
                    break;
                case 1://最大值法
                    Result = r > g ? r : g;
                    Result = Result > b ? Result : b;
                    break;
                case 2://加权平均值法
                    Result = ((int)(0.7 * r) + (int)(0.2 * g) + (int)(0.1 * b));
                    break;
            }
            bitmap.SetPixel(x, y, Color.FromArgb(Result, Result, Result));
        }
    this.pictureBox1.Image = bitmap;
}