asp.net 为指定的图片生成缩图

程序代码

#region 为指定的图片生成缩略图
        /// <summary>
        /// 为指定的图片生成缩图
        /// <para>color != null，则不变形</para>
        /// </summary>
        /// <param name="sourcepath">源图的完整硬盘路径，包括文件名</param>
        /// <param name="maxwidth">缩图宽度</param>
        /// <param name="maxheight">缩图高度</param>
        /// <param name="color">指定背景色，可传null</param>
        /// <param name="bmpath">缩图的完整硬盘目录，以/结束，不包括文件名</param>
        /// <returns>是否成功</returns>
        public static bool Thumbnail(string sourcepath, int maxwidth, int maxheight, Color color, string bmpath)
        {
            string filename = Path.GetFileNameWithoutExtension(sourcepath); //拿到没有后缀的文件名
            string fileExt = Path.GetExtension(sourcepath).ToLower(); //取得扩展名
            if (fileExt.IsNullOrEmpty()) //如果取不到文件后缀,就认为传入路径是错误的
                return false;

            int ActualWidth = 0;  //图片实际宽度
            int ActualHeight = 0; //图片实际高度
            int Srcx = 0;         //图片左边距
            int Srcy = 0;         //图片上边距

            Image newImg;            
            using (Image oriImg = Image.FromFile(sourcepath))
            {
                if ((maxwidth < oriImg.Width) || (maxheight < oriImg.Height)) //执行按比例缩小
                {
                    if (maxwidth.toString() / maxheight.toString() > oriImg.Width.toString() / oriImg.Height.toString(0f)) //以高度为准计算
                    {
                        ActualWidth = maxheight * oriImg.Width / oriImg.Height;
                        ActualHeight = maxheight;
                        Srcx = (maxwidth - ActualWidth) / 2;
                    }
                    else
                    {
                        ActualWidth = maxwidth;
                        ActualHeight = maxwidth * oriImg.Height / oriImg.Width;
                        Srcy = (maxheight - ActualHeight) / 2;
                    }
                }
                else
                {
                    ActualWidth = oriImg.Width;
                    ActualHeight = oriImg.Height;
                    Srcx = (maxwidth - ActualWidth) / 2;
                    Srcy = (maxheight - ActualHeight) / 2;
                } //以上操作完成后,得到缩图的宽与高,下面生成缩图,并保存到缩图文件夹                

                //根据颜色判断是否产生固定大小的缩图
                newImg = color == null ? new Bitmap(ActualWidth, ActualHeight) : new Bitmap(maxwidth, maxheight);
                using (Graphics g = Graphics.FromImage(newImg)) //把新图形加载进Graphice对象中
                {
                    if (color != null)
                        g.Clear(color); //声明背景色
                    else
                    {
                        Srcx = 0;
                        Srcy = 0;
                    }

                    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                    g.InterpolationMode = InterpolationMode.HighQualityBicubic; //指定高质量插值法,关键在于HighQualityBicubic
                    g.DrawImage(oriImg, new Rectangle(Srcx, Srcy, ActualWidth, ActualHeight), 0, 0, oriImg.Width, oriImg.Height, GraphicsUnit.Pixel);
                }
            } //到这里，源图，画板均可以释放了

            switch (fileExt)
            {
                case ".jpg":
                    newImg.Save(bmpath + filename + ".jpg", ImageFormat.Jpeg);
                    break;
                case ".gif":
                    newImg.Save(bmpath + filename + ".gif", ImageFormat.Gif);
                    break;
                case ".png":
                    newImg.Save(bmpath + filename + ".png", ImageFormat.Png);
                    break;
                default:
                    newImg.Save(bmpath + filename + ".jpg", ImageFormat.Jpeg);
                    break;
            }
            newImg.Dispose();
            return true;
        }
        #endregion