图像变成黑白

在写代码之前，先在工程的 属性-->生成-->勾选 “允许不安全代码“

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 public Bitmap ConvertBmp(System.Drawing.Bitmap bmp, int mode)        {            bool ret = true;                         int w = bmp.Width;            int h = bmp.Height;            try            {                byte newColor = 0;                BitmapData srcData = bmp.LockBits(new Rectangle(0, 0, w, h), ImageLockMode.ReadWrite, PixelFormat.Gdi);                unsafe                {                    byte* p = (byte*)srcData.Scan0.ToPointer();                    for (int y = 0; y < h; y++)                    {                        for (int x = 0; x < w; x++)                        {                            if (mode == 0)　// 加权平均                            {                                newColor = (byte)((float)p[0] * 0.114f + (float)p[1] * 0.587f + (float)p[2] * 0.299f);                            }                            else　　　　// 算数平均                            {                                newColor = (byte)((float)(p[0] + p[1] + p[2]) / 3.0f);                            }                            p[0] = newColor;                            p[1] = newColor;                            p[2] = newColor;                            p += 3;                        }                        p += srcData.Stride - w * 3;                    }                    bmp.UnlockBits(srcData);                    return bmp;                }            }            catch            {                return null;            }        }