下面代码可以获取差异部分，但是相同部分为黑色，经过多次修改还是不行，
如果用像素点一个个循环设置，又耗时太久，有那位大神可以看看下面的，能有快速办法么
 public static Bitmap DifCompare(Bitmap bmp1, Bitmap bmp2, Size block)
        {
            List<Rectangle> rects = new List<Rectangle>();
            PixelFormat pf = PixelFormat.Format24bppRgb;

            Bitmap difBitmap = new Bitmap(bmp2.Width, bmp2.Height, pf);

            BitmapData bd1 = bmp1.LockBits(new Rectangle(0, 0, bmp1.Width, bmp1.Height), ImageLockMode.ReadWrite, pf);
            BitmapData bd2 = bmp2.LockBits(new Rectangle(0, 0, bmp2.Width, bmp2.Height), ImageLockMode.ReadWrite, pf);
            BitmapData bd3 = difBitmap.LockBits(new Rectangle(0, 0, difBitmap.Width, difBitmap.Height), ImageLockMode.ReadWrite, pf);
            try
            {
                unsafe
                {
                    int w = 0, h = 0;
                    ;
                    while (h < bd1.Height && h < bd2.Height)
                    {
                        byte* p1 = (byte*)bd1.Scan0 + h * bd1.Stride;
                        byte* p2 = (byte*)bd2.Scan0 + h * bd2.Stride;
                        byte* p3 = (byte*)bd3.Scan0 + h * bd3.Stride;
                        w = 0;
                        Color c = Color.Transparent;
                      
                        while (w < bd1.Width && w < bd2.Width)
                        {
                            //按块大小进行扫描
                            for (int i = 0; i < block.Width; i++)
                            {
                                int wi = w + i;
                                if (wi >= bd1.Width || wi >= bd2.Width) break;


                                for (int j = 0; j < block.Height; j++)
                                {
                                    int hj = h + j;
                                    if (hj >= bd1.Height || hj >= bd2.Height) break;

                                    ICColor* pc1 = (ICColor*)(p1 + wi * 3 + bd1.Stride * j);
                                    ICColor* pc2 = (ICColor*)(p2 + wi * 3 + bd2.Stride * j);
                                    ICColor* pc3 = (ICColor*)(p3 + wi * 3 + bd3.Stride * j);
                                    if (pc1->R != pc2->R || pc1->G != pc2->G || pc1->B != pc2->B)
                                    {
                                        //当前块有某个象素点颜色值不相同.也就是有差异.
                                        int bw = Math.Min(block.Width, bd1.Width - w);
                                        int bh = Math.Min(block.Height, bd1.Height - h);
                                        rects.Add(new Rectangle(w, h, bw, bh));

                                        pc3[0] = pc2[0];
                                        pc3[1] = pc2[1];
                                        pc3[2] = pc2[2];
                                      
                                    }
                                }
                            }                     
                        }

                        h += block.Height;
                    }
                }
            }
            finally
            {
                bmp1.UnlockBits(bd1);
                bmp2.UnlockBits(bd2);
                difBitmap.UnlockBits(bd3);
            }
            return difBitmap;
        }