C#无损高质量压缩图片实现代码

/// <summary>
/// 无损压缩图片
/// </summary>
/// <param name="sFile">原图片地址</param>
/// <param name="dFile">压缩后保存图片地址</param>
/// <param name="flag">压缩质量（数字越小压缩率越高）1-100</param>
/// <param name="size">压缩后图片的最大大小</param>
/// <param name="sfsc">是否是第一次调用</param>
/// <returns></returns>
public static bool CompressImage(string sFile, string dFile, int flag = 90, int size = 300, bool sfsc = true)
{
 Image iSource = Image.FromFile(sFile);
 ImageFormat tFormat = iSource.RawFormat;
 //如果是第一次调用，原始图像的大小小于要压缩的大小，则直接复制文件，并且返回true
 FileInfo firstFileInfo = new FileInfo(sFile);
 if (sfsc == true && firstFileInfo.Length < size * 1024)
 {
 firstFileInfo.CopyTo(dFile);
 return true;
 }

 int dHeight = iSource.Height / 2;
 int dWidth = iSource.Width / 2;
 int sW = 0, sH = 0;
 //按比例缩放
 Size tem_size = new Size(iSource.Width, iSource.Height);
 if (tem_size.Width > dHeight || tem_size.Width > dWidth)
 {
 if ((tem_size.Width * dHeight) > (tem_size.Width * dWidth))
 {
  sW = dWidth;
  sH = (dWidth * tem_size.Height) / tem_size.Width;
 }
 else
 {
  sH = dHeight;
  sW = (tem_size.Width * dHeight) / tem_size.Height;
 }
 }
 else
 {
 sW = tem_size.Width;
 sH = tem_size.Height;
 }

 Bitmap ob = new Bitmap(dWidth, dHeight);
 Graphics g = Graphics.FromImage(ob);

 g.Clear(Color.WhiteSmoke);
 g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
 g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

 g.DrawImage(iSource, new Rectangle((dWidth - sW) / 2, (dHeight - sH) / 2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);

 g.Dispose();

 //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)
 {
  ob.Save(dFile, jpegICIinfo, ep);//dFile是压缩后的新路径
  FileInfo fi = new FileInfo(dFile);
  if (fi.Length > 1024 * size)
  {
  flag = flag - 10;
  CompressImage(sFile, dFile, flag, size, false);
  }
 }
 else
 {
  ob.Save(dFile, tFormat);
 }
 return true;
 }
 catch
 {
 return false;
 }
 finally
 {
 iSource.Dispose();
 ob.Dispose();
 }
}