生成缩率图项目实例

 /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="fileName">源图路径（绝对路径）</param>
        /// <param name="newFileName">缩略图路径（绝对路径）</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="mode">"HW":指定高宽缩放（不变形）</param>    
        public static void MakeThumbnailImage(string fileName, string newFileName, int width, int height, string mode)
        {
            Image originalImage = Image.FromFile(fileName);
            int Imgwidth = width;
            int Imgheight = height;


            int towidth = width;
            int toheight = height;
            int tox = 0;
            int toy = 0;

            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;

            switch (mode)
            {
                case "HW"://等高宽缩放（不变形）
                    if ((double)ow / (double)oh > (double)towidth / (double)toheight)
                    {
                        towidth = width;
                        toheight = Convert.ToInt32((double)oh * (double)towidth / (double)ow);
                        toy = (height - toheight) / 2;

                        Imgwidth = width;
                        Imgheight = height;
                    }
                    else 
                    {
                        toheight = height;
                        towidth = Convert.ToInt32((double)ow * (double)toheight / (double)oh);
                        tox = (width - towidth) / 2;

                        
                    }
                    break;

                case "W"://指定宽，高按比例           
                    towidth = originalImage.Width > width ? width : originalImage.Width;
                    toheight = originalImage.Height * towidth / originalImage.Width;

                    Imgwidth = towidth;
                    Imgheight = toheight;
                    break;
                case "H"://指定高，宽按比例
                    toheight = originalImage.Height > height ? height : originalImage.Height;
                    towidth = originalImage.Width * toheight / originalImage.Height;

                    Imgwidth = towidth;
                    Imgheight = toheight;
                    break;
                case "Cut"://指定高宽裁减（不变形）                
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }

                    Imgwidth = width;
                    Imgheight = height;
                    break;
                default:
                    break;
            }


            //新建一个bmp图片
            Bitmap b = new Bitmap(Imgwidth, Imgheight);
            try
            {
                //新建一个画板
                Graphics g = Graphics.FromImage(b);
                //设置高质量插值法
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                //设置高质量,低速度呈现平滑程度
                g.SmoothingMode = SmoothingMode.HighQuality;
                g.PixelOffsetMode = PixelOffsetMode.HighQuality;
                g.CompositingQuality = CompositingQuality.HighQuality;
                //清空画布并以透明背景色填充
                g.Clear(Color.Transparent);
                //在指定位置并且按指定大小绘制原图片的指定部分
                g.DrawImage(originalImage, new Rectangle(tox, toy, towidth, toheight), new Rectangle(0, 0, ow, oh), GraphicsUnit.Pixel);

                SaveImage(b, newFileName, GetCodecInfo("image/" + GetFormat(newFileName).ToString().ToLower()));
                g.Dispose();
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {

                originalImage.Dispose();
                b.Dispose();
            }
        }