高质量图片缩略图生成（编程笔记）

        /// <summary>/// 生成缩略图/// </summary>/// <param name="maxWidth">生成的缩略图最大宽度</param>/// <param name="maxHeight">生成的缩略图最大高度</param>/// <param name="imgFileStream">图片文件流对象</param>/// <param name="savePath">文件保存路径</param>/// <param name="imgFormat">生成图片的格式</param>public void GenerateThumbnail(int maxWidth, int maxHeight, System.IO.Stream imgFileStream, string savePath,System.Drawing.Imaging.ImageFormat imgFormat){using (var img = System.Drawing.Image.FromStream(imgFileStream)){var sourceWidth = img.Width;var sourceHeight = img.Height;var thumbWidth = sourceWidth; //要生成的缩略图的宽度var thumbHeight = sourceHeight; //要生成的缩略图的高度//计算生成图片的高度和宽度if (sourceWidth > maxWidth || sourceHeight > maxHeight){var rateWidth = (double)sourceWidth / maxWidth;var rateHeight = (double)sourceHeight / maxHeight;if (rateWidth > rateHeight){thumbWidth = maxWidth;thumbHeight = (int)Math.Round(sourceHeight / rateWidth);}else{thumbWidth = (int)Math.Round(sourceWidth / rateHeight);thumbHeight = maxHeight;}}using (var bmp = new System.Drawing.Bitmap(thumbWidth, thumbHeight)){//从Bitmap创建一个System.Drawing.Graphics对象，用来绘制高质量的缩小图。using (var gr = System.Drawing.Graphics.FromImage(bmp)){//设置 System.Drawing.Graphics对象的SmoothingMode属性为HighQualitygr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;//下面这个也设成高质量gr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;//下面这个设成Highgr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;//把原始图像绘制成上面所设置宽高的缩小图var rectDestination = new System.Drawing.Rectangle(0, 0, thumbWidth, thumbHeight);gr.DrawImage(img, rectDestination, 0, 0, sourceWidth, sourceHeight,System.Drawing.GraphicsUnit.Pixel);//保存图像bmp.Save(savePath, imgFormat);}}}}

        protected void Button4_Click(object sender, EventArgs e){GenerateThumbnail(500, 500, FileUpload1.PostedFile.InputStream, "d:/1.jpg",System.Drawing.Imaging.ImageFormat.Jpeg);}