生成缩略图

 public Image ThumbImg(Image sourceImage)
        {
            int thumbwidth = 600;
            int width = sourceImage.Width;
            int height = sourceImage.Height;
            if (thumbwidth >= width)
            {
                return sourceImage;
            }
            else
            {
                Image imgThumb = new System.Drawing.Bitmap(thumbwidth, height * thumbwidth / width);
                System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(imgThumb);
                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                g.DrawImage(sourceImage, new Rectangle(0, 0, thumbwidth, height * thumbwidth / width), 0, 0, width, height, GraphicsUnit.Pixel);
                g.Dispose();
                return imgThumb;
            }
        }