/// <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)
{
//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trueFileInfo firstFileInfo = new FileInfo(sFile);if (sfsc == true && firstFileInfo.Length < size * 1024){firstFileInfo.CopyTo(dFile);return true;}Image iSource = Image.FromFile(sFile);
    ImageFormat tFormat = iSource.RawFormat;

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1-100EncoderParameter 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();}
}