缩图

        private byte[] GetThumbnailFromImage(Stream imgStream, int size, string format)
        {
            System.Drawing.Image image = System.Drawing.Image.FromStream(imgStream);
            int newWidth, newHeight;
            if (image.Width >= image.Height)
            {
                newWidth = size;
                newHeight = size * image.Height / image.Width;
            }
            else
            {
                newHeight = size;
                newWidth = size * image.Width / image.Height;
            }
            System.Drawing.Image newImg = image.GetThumbnailImage(newWidth, newHeight, null, IntPtr.Zero);
            using (MemoryStream ms = new MemoryStream())
            {
                newImg.Save(ms, format == "JPG" ? System.Drawing.Imaging.ImageFormat.Jpeg : System.Drawing.Imaging.ImageFormat.Png);
                return ms.ToArray();
            }
        }