C# ppc中，如何正确保存调整大小后的图片？

public static void Resized(string imageFile , string newImageFile)
{
Bitmap srcmap = new Bitmap(imageFile);
Bitmap destbit = new Bitmap(128 , 128);

Rectangle srcRec = new Rectangle(0 , 0 , srcmap.Width , srcmap.Width);
Rectangle destRec = new Rectangle(0 , 0 , 320 , 240);

Graphics g = Graphics.FromImage(destbit);
g.DrawImage(srcmap , destRec , srcRec , GraphicsUnit.Pixel);

destbit.Save(newImageFile , System.Drawing.Imaging.ImageFormat.Bmp);
}