C# 按质量等级压缩图片

采用的压缩方式跟上一篇是一样的，不同的是，这次我们会同时融入一个等比压缩宽高的方法，这两个一起使用，会使文件空间大幅度减小，同时也可以单独压缩宽高，质量等级不要变（直接用100即可）；

实现功能：

压缩图片大小以及质量

开发环境：

开发工具：Visual Studio 2013

.NET Framework版本：4.5

实现代码：

//选择图片路径 
private void btnOld_Click(object sender, EventArgs e) 
{    
   OpenFileDialog ofd = new OpenFileDialog();     
   ofd.Filter = "图片|*.jpg;*.jpeg;*.png";     
   if (ofd.ShowDialog() == DialogResult.OK)     
　　{        
　　　　txtOld.Text = ofd.FileName;   
    }
}
 //选择保存路径 
private void btnNew_Click(object sender, EventArgs e) 
{     
　　FolderBrowserDialog fbd = new FolderBrowserDialog();  
   fbd.ShowNewFolderButton = true;   
  if (fbd.ShowDialog() == DialogResult.OK)  
   {         
　　　　txtNew.Text = fbd.SelectedPath;   
   }
 }
//压缩
private void btnCompressSize_Click(object sender, EventArgs e)
{   
　　 ImgSizeCompress(10L);
     ImgSizeCompress(50L);
    ImgSizeCompress(70L);    
   MessageBox.Show("成功");
}
//压缩方法   
private void ImgSizeCompress(long level)   
{      
　　 Image img = Image.FromFile(txtOld.Text);    
     ImageFormat imgFormat = img.RawFormat;
     Size newSize = new Size(img.Width / 2, img.Height / 2);     
     Bitmap outBmp = new Bitmap(newSize.Width, newSize.Height);
     Graphics g = Graphics.FromImage(outBmp);   
     g.CompositingQuality = CompositingQuality.HighQuality;  
     g.SmoothingMode = SmoothingMode.HighQuality;   
     g.InterpolationMode = InterpolationMode.HighQualityBicubic;    
     g.DrawImage(img, new Rectangle(0, 0, newSize.Width, newSize.Height), 0, 0, img.Width, img.Height, GraphicsUnit.Pixel);     
     g.Dispose();      
     img.Dispose();
     EncoderParameters encoderParams = new EncoderParameters();      
     encoderParams.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, level);
     ImageCodecInfo codecInfo = GetEncoder(imgFormat);      
     string savePath = txtNew.Text + "\\" + DateTime.Now.Ticks + "." + codecInfo.FormatDescription;       
     outBmp.Save(savePath, codecInfo, encoderParams);      
     outBmp.Dispose();
 }
 private ImageCodecInfo GetEncoder(ImageFormat format) 
{     
　　ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();    
    foreach (ImageCodecInfo codec in codecs)     
    {         
      if (codec.FormatID == format.Guid)         
     {            
       return codec;         
     } 
    }    
   return null;
 }