在c#中图片原比例缩放

在c#中图片原比例缩放
cs中的一种写法.要引用using System.IO;

  string image_path = this.MapPath("~/work/" + Logo.jpg);
                ImageButtonLogo.Width = 120;
                ImageButtonLogo.Height = 90;
                ImageButtonLogo.ImageUrl = ResolveUrl("~/work/" + Logo.jpg);
                if (File.Exists(image_path))
                {
                    System.Drawing.Image img = System.Drawing.Image.FromFile(image_path);

                    double _width = img.Size.Width;
                    double _height = img.Size.Height;
                    double _zoom_factor = _width / 120;
                    if (_height / 90 > _zoom_factor) _zoom_factor = _height / 90;
                    if (_zoom_factor > 1)
                    {
                        ImageButtonLogo.Width = Convert.ToInt32(_width / _zoom_factor);
                        ImageButtonLogo.Height = Convert.ToInt32(_height / _zoom_factor);
                    }
                }
                else
                {
                    ImageButtonLogo.ImageUrl = ResolveUrl("~/work/default.jpg");
                }