C#图片处理如何生成缩略图的实现

 
        public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, ThumbnailMode mode)
        {
            System.Drawing.Image img_OriginalImage = null;
            ImageFormat tFormat = null;
            try
            {
                img_OriginalImage = (Bitmap)System.Drawing.Image.FromFile(originalImagePath);
                tFormat = img_OriginalImage.RawFormat;
            }
            catch (Exception ex)
            {
                if (img_OriginalImage != null)
                {
                    img_OriginalImage.Dispose();
                }
               
                throw new Exception("压缩图片:" + originalImagePath + "失败！\r\n" + ex.Message);
 
            }
 
            int i_ToWidth = width;
            int i_ToHeight = height;
 
            int x = 0;
            int y = 0;
 
            int i_OriginalWidth = img_OriginalImage.Width;
            int i_OriginalHeight = img_OriginalImage.Height;
 
            switch (mode)
            {
                case ThumbnailMode.Width:
                    i_ToHeight = img_OriginalImage.Height * width / img_OriginalImage.Width;
                    break;
                case ThumbnailMode.Height:
                    i_ToWidth = img_OriginalImage.Width * height / img_OriginalImage.Height;
                    break;
                case ThumbnailMode.Cut:
                    if ((double)img_OriginalImage.Width / (double)img_OriginalImage.Height > (double)i_ToWidth / (double)i_ToHeight)
                    {
                        i_OriginalHeight = img_OriginalImage.Height;
                        i_OriginalWidth = img_OriginalImage.Height * i_ToWidth / i_ToHeight;
                        y = 0;
                        x = (img_OriginalImage.Width - i_OriginalWidth) / 2;
                    }
                    else
                    {
                        i_OriginalWidth = img_OriginalImage.Width;
                        i_OriginalHeight = img_OriginalImage.Width * height / i_ToWidth;
                        x = 0;
                        y = (img_OriginalImage.Height - i_OriginalHeight) / 2;
                    }
                    break;
                default:
                    break;
            }
 
            //新建一个BMP图片
            System.Drawing.Image img_BitMap = new System.Drawing.Bitmap(i_ToWidth, i_ToHeight);
            //新建一个画板
            System.Drawing.Graphics gp = Graphics.FromImage(img_BitMap);
            //设置高质量插值法
            gp.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            //设置高质量、低速度呈现平滑程度
            gp.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            gp.CompositingQuality = CompositingQuality.HighQuality;
 
            //清空画布并以透明背景色填充
            gp.Clear(Color.Transparent);
            //指定位置并按大小绘制原图片的指定部分
            gp.DrawImage(img_OriginalImage, new Rectangle(0, 0, i_ToWidth, i_ToHeight), new Rectangle(x, y, i_OriginalWidth, i_OriginalHeight), GraphicsUnit.Pixel);
 
            try
            {
                EncoderParameters ep = new EncoderParameters();
                long[] qy = new long[1];
                qy[0] = 100;//设置压缩的比例1-100  
                EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
                ep.Param[0] = eParam;
 
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo jpegICIinfo = null;
                for (int i = 0; i < arrayICI.Length; i++)
                {
                    if (arrayICI[i].FormatDescription.Equals("JPEG"))
                    {
                        jpegICIinfo = arrayICI[i];
                        break;
                    }
                }
                if (jpegICIinfo != null && Equals(tFormat, ImageFormat.Jpeg))
                {
                    //以JPG格式保存图片
                    img_BitMap.Save(thumbnailPath, jpegICIinfo, ep);
                    //Const.iSuccessCount++;
                }
                else
                {
                    img_BitMap.Save(thumbnailPath, tFormat);
                    //Const.iSuccessCount++;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("复制图片:" + originalImagePath + "失败！\r\n" + ex.Message + ex.StackTrace);
            }
            finally
            {
                if (img_OriginalImage != null)
                {
                    img_OriginalImage.Dispose();
                }
                if (img_BitMap != null)
                {
                    img_BitMap.Dispose();
                }
                if (gp != null)
                {
                    gp.Dispose();
                }
                //GC.Collect();
            }
        }

public enum ThumbnailMode
    {
        /// <summary>
        /// 指定宽度，高度按照比例缩放
        /// </summary>
        Width = 0,
 
        /// <summary>
        /// 指定高度，宽度按照比例缩放
        /// </summary>
        Height = 1,
 
        /// <summary>
        /// 按照指定的高度和宽度剪裁
        /// </summary>
        Cut = 2,
 
        /// <summary>
        /// 指定宽度，高度按照比例缩放
        /// </summary>
        None = 3
    }