C#实现图片压缩方法

原文地址：http://www.cnblogs.com/lifeil/archive/2013/02/25/2931683.html

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：

        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：

        public Bitmap GetImageThumb(Bitmap mg, Size newSize)        {            double ratio = 0d;            double myThumbWidth = 0d;            double myThumbHeight = 0d;            int x = 0;            int y = 0;            Bitmap bp;            if ((mg.Width / Convert.ToDouble(newSize.Width)) > (mg.Height /            Convert.ToDouble(newSize.Height)))                ratio = Convert.ToDouble(mg.Width) / Convert.ToDouble(newSize.Width);            else                ratio = Convert.ToDouble(mg.Height) / Convert.ToDouble(newSize.Height);            myThumbHeight = Math.Ceiling(mg.Height / ratio);            myThumbWidth = Math.Ceiling(mg.Width / ratio);            Size thumbSize = new Size((int)newSize.Width, (int)newSize.Height);            bp = new Bitmap(newSize.Width, newSize.Height);            x = (newSize.Width - thumbSize.Width) / 2;            y = (newSize.Height - thumbSize.Height);            System.Drawing.Graphics g = Graphics.FromImage(bp);            g.SmoothingMode = SmoothingMode.HighQuality;            g.InterpolationMode = InterpolationMode.HighQualityBicubic;            g.PixelOffsetMode = PixelOffsetMode.HighQuality;            Rectangle rect = new Rectangle(x, y, thumbSize.Width, thumbSize.Height);            g.DrawImage(mg, rect, 0, 0, mg.Width, mg.Height, GraphicsUnit.Pixel);            return bp;        }

这样实现的压缩使压缩率大幅度上升。其实代码并没有变多少，最主要的是在保存的时候要是用jpg格式，如果不指定格式，默认使用的是png格式。

下面这个是园友写的根据设置图片质量数值来压缩图片的方法：

 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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