C#修改图片分辨率

FileStream fs = new FileStream(@"C:\aaa.JPG", FileMode.Open);
               Bitmap img1 = new Bitmap(fs);

                Bitmap img2 = new Bitmap(1024, 768, PixelFormat.Format24bppRgb);
                img2.SetResolution(900.0F, 900.0F);
                using(Graphics g = Graphics.FromImage(img2))
               {
                   g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                   g.DrawImage(img1, new Rectangle(0, 0, img2.Width, img2.Height), 0, 0, img1.Width, img1.Height, GraphicsUnit.Pixel);
                   g.Dispose();

                   img2.Save(@"d:\yyyyy.bmp", ImageFormat.Bmp);
               }

public static Bitmap KiResizeImage(Bitmap bmp, int newW, int newH)
        {
            try
            {
                Bitmap b = new Bitmap(newW, newH);
                Graphics g = Graphics.FromImage(b);
                // 插值算法的质量 
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                g.DrawImage(bmp, new Rectangle(0, 0, newW, newH), new Rectangle(0, 0, bmp.Width, bmp.Height), GraphicsUnit.Pixel);
                g.Dispose();
                return b;
            }
            catch
            {
                return null;
            }
        }