C#图片按比例缩放

// 按比例缩放图片
        public Image ZoomPicture(Image SourceImage, int TargetWidth, int TargetHeight)
        {
            int IntWidth; //新的图片宽
            int IntHeight; //新的图片高
            try
            {
                System.Drawing.Imaging.ImageFormat format = SourceImage.RawFormat;
                System.Drawing.Bitmap SaveImage = new System.Drawing.Bitmap(TargetWidth, TargetHeight);
                Graphics g = Graphics.FromImage(SaveImage);
                g.Clear(Color.White);

                //计算缩放图片的大小 http://www.cnblogs.com/roucheng/

                if (SourceImage.Width > TargetWidth && SourceImage.Height <= TargetHeight)//宽度比目的图片宽度大，长度比目的图片长度小
                {
                    IntWidth = TargetWidth;
                    IntHeight = (IntWidth * SourceImage.Height) / SourceImage.Width;
                }
                else if (SourceImage.Width <= TargetWidth && SourceImage.Height > TargetHeight)//宽度比目的图片宽度小，长度比目的图片长度大
                {
                    IntHeight = TargetHeight;
                    IntWidth = (IntHeight * SourceImage.Width) / SourceImage.Height;
                }
                else if (SourceImage.Width <= TargetWidth && SourceImage.Height <= TargetHeight) //长宽比目的图片长宽都小
                {
                    IntHeight = SourceImage.Width;
                    IntWidth = SourceImage.Height;
                }
                else//长宽比目的图片的长宽都大
                {
                    IntWidth = TargetWidth;
                    IntHeight = (IntWidth * SourceImage.Height) / SourceImage.Width;
                    if (IntHeight > TargetHeight)//重新计算
                    {
                        IntHeight = TargetHeight;
                        IntWidth = (IntHeight * SourceImage.Width) / SourceImage.Height;
                    }
                }

                g.DrawImage(SourceImage, (TargetWidth - IntWidth) / 2, (TargetHeight - IntHeight) / 2, IntWidth, IntHeight);
                SourceImage.Dispose();

                return SaveImage;
            }
            catch (Exception ex)
            {
              
            }

            return null;
        }