减少图片分辨率

Color c=new Color();
            Bitmap box1=new Bitmap(pictureBox1.Image);
            Bitmap box2=new Bitmap(pictureBox2.Image);
            int r,g,b,i,j,k1,k2,size,xres,yres;
            xres=pictureBox1.Image.Width;
            yres=pictureBox1.Image.Height;
            size=2;
            for(i=0;i<=xres-1;i+=size)
            {
                for(j=0;j<=yres-1;j+=size)
                {
                    c=box1.GetPixel(i,j);
                    r=c.R;g=c.G;b=c.B;
                    Color cc=Color.FromArgb(r,g,b);
                    for(k1=0;k1<=size-1;k1++)
                        for(k2=0;k2<=size-1;k2++)
                            box2.SetPixel(i+k1,j+k2,cc);
                }
            }
            pictureBox2.Refresh();
            pictureBox2.Image=box2;