c# 如何实现图片压缩

一般在web应用中，对客户端提交上来的图片肯定需要进行压缩的。尤其是比较大的图片，如果不经过压缩会导致页面变的很大，打开速度比较慢，当然了如果是需要高质量的图片也得需要生产缩略图。

下面贴出我自己琢磨的图片压缩算法，首先这个是未经优化的简单实现： 

代码如下:

        public static System.Drawing.Image GetImageThumb(System.Drawing.Image sourceImg, int width, int height)
        {
            System.Drawing.Image targetImg = new System.Drawing.Bitmap(width, height);
            using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(targetImg))
            {
                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
                g.DrawImage(sourceImg, new System.Drawing.Rectangle(0, 0, width, height), new System.Drawing.Rectangle(0, 0, sourceImg.Width, sourceImg.Height), System.Drawing.GraphicsUnit.Pixel);
                g.Dispose();
            }
            return targetImg;
        }

这个方法比较简单，用到的是高质量压缩。经过这个方法压缩后，200K的图片只能压缩到160k左右。经过改写代码实现了如下的方法： 

代码如下:

        public static bool GetPicThumbnail(string sFile, string outPath, int flag)
        {
            System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile);
            ImageFormat tFormat = iSource.RawFormat;
            //以下代码为保存图片时，设置压缩质量 
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = flag;//设置压缩的比例1-100 
            EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
            ep.Param[0] = eParam;
            try
            {
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo jpegICIinfo = null;
                for (int x = 0; x < arrayICI.Length; x++)
                {
                    if (arrayICI[x].FormatDescription.Equals("JPEG"))
                    {
                        jpegICIinfo = arrayICI[x];
                        break;
                    }
                }
                if (jpegICIinfo != null)
                {
                    iSource.Save(outPath, jpegICIinfo, ep);//dFile是压缩后的新路径 
                }
                else
                {
                    iSource.Save(outPath, tFormat);
                }
                return true;
            }
            catch
            {
                return false;
            }
            finally
            {
                iSource.Dispose();
                iSource.Dispose();
            }
        }

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