马赛克效果

 Color C;
            int r, g, b, rV, gV, bV, rT, gT, bT, y, z;
            Bitmap bmp = new Bitmap(pictureBox1.Image);//创建Bitmap对象
            Bitmap tmp = (Bitmap)bmp.Clone();
            //马赛克为5*5阵列
            for (int i = 0; i < bmp.Width - 5; i += 5)
                for (int j = 0; j < bmp.Height - 5; j += 5)
                {
                    rT = 0; gT = 0; bT = 0;
                    //获取区域块的像素颜色分量值
                    for (y = 0; y <= 5; y++)
                        for (z = 0; z <= 5; z++)
                        {
                            C = bmp.GetPixel(i + y, j + z);
                            r = C.R;
                            g = C.G;
                            b = C.B;
                            rT = rT + r;
                            gT = gT + g;
                            bT = bT + b;
                        }
                    //取平均值
                    rV = (int)rT / 25;
                    gV = (int)gT / 25;
                    bV = (int)bT / 25;
                    //处理颜色值溢出
                    rV = rV > 255 ? 255 : rV;
                    rV = rV < 0 ? 0 : rV;
                    gV = gV > 255 ? 255 : gV;
                    gV = gV < 0 ? 0 : gV;
                    bV = bV > 255 ? 255 : bV;
                    bV = bV < 0 ? 0 : bV;
                    //用平均值绘制5*5区域图像
                    for (y = 0; y <= 5; y++)
                        for (z = 0; z <= 5; z++)
                            tmp.SetPixel(i + y, j + z, Color.FromArgb(rV, gV, bV));
                }
            pictureBox2.Image = tmp;