如何用ZLib对流进行压缩及解压呀？

Question

    jpg.SaveToStream(m1); //将JPG图象写入流中
    jpg.free;如果用ZLIB对流进行压缩与解压缩呀？

Answer 1

这方面文章很多，可以自已找一下。压缩图像     procedure CompressBitmap(var CompressedStream: TMemoryStream;const 
      CompressionLevel: TCompressionLevel); 
    var 
      SourceStream: TCompressionStream; 
      DestStream: TMemoryStream; 
      Count: Integer; 
    Begin 
      //获得图像流的原始尺寸 
      Count := CompressedStream.Size; 
      DestStream := TMemoryStream.Create; 
      SourceStream := TCompressionStream.Create(CompressionLevel, DestStream); 
      Try 
        //SourceStream中保存着原始的图像流 
        CompressedStream.SaveToStream(SourceStream); 
        //将原始图像流进行压缩， DestStream中保存着压缩后的图像流 
        SourceStream.Free; 
        CompressedStream.Clear; 
        //写入原始图像的尺寸 
        CompressedStream.WriteBuffer(Count, SizeOf(Count)); 
        //写入经过压缩的图像流 
        CompressedStream.CopyFrom(DestStream, 0); 
      finally 
        DestStream.Free; 
      end; 
    end; 还原被压缩图像 
   procedure UnCompressBitmap(const CompressedStream: TFileStream; var Bmp: 
      TBitmap); 
   var 
      SourceStream: TDecompressionStream; 
      DestStream: TMemoryStream; 
      Buffer: PChar; 
      Count: Integer; 
   Begin 
      //从被压缩的图像流中读出原始图像的尺寸 
      CompressedStream.ReadBuffer(Count, SizeOf(Count)); 
      //根据图像尺寸大小为将要读入的原始图像流分配内存块 
      GetMem(Buffer, Count); 
      DestStream := TMemoryStream.Create; 
      SourceStream := TDecompressionStream.Create(CompressedStream); 
      Try 
        //将被压缩的图像流解压缩，然后存入 Buffer内存块中 
        SourceStream.ReadBuffer(Buffer^, Count); 
        //将原始图像流保存至 DestStream流中 
        DestStream.WriteBuffer(Buffer^, Count); 
        DestStream.Position := 0;//复位流指针 
        //从 DestStream流中载入原始图像流 
        Bmp.LoadFromStream(DestStream); 
      finally 
        FreeMem(Buffer); 
        DestStream.Free; 
      end; 
    end; 

Answer 2

//Zlib的使用
uses
  ZLib, Classes;procedure Compress(CompressedStream: TMemoryStream);
var
  SourceStream: TCompressionStream;
  DestStream: TMemoryStream;
  Count: Integer;
begin
  Count := CompressedStream.Size;
  DestStream := TMemoryStream.Create;
  SourceStream := TCompressionStream.Create(clMax, DestStream);
  try
    CompressedStream.SaveToStream(SourceStream);
    SourceStream.Free;
    CompressedStream.Clear;
    CompressedStream.WriteBuffer(Count, SizeOf(Count));
    CompressedStream.CopyFrom(DestStream, 0);
  finally
    DestStream.Free;
  end;
end;procedure UnCompress(CompressedStream: TMemoryStream);
var
  SourceStream: TDecompressionStream;
  DestStream: TMemoryStream;
  Buffer: PChar;
  Count: integer;
begin
  CompressedStream.Seek(0, soFromBeginning);
  CompressedStream.ReadBuffer(Count, SizeOf(Count));
  GetMem(Buffer, Count);
  DestStream := TMemoryStream.Create;
  SourceStream := TDecompressionStream.Create(CompressedStream);
  try
    SourceStream.ReadBuffer(Buffer^, Count);
    DestStream.WriteBuffer(Buffer^, Count);
    DestStream.Position := 0;
    CompressedStream.LoadFromStream(DestStream);
  finally
    FreeMem(Buffer);
    DestStream.Free;
  end;
end;

Answer 3

JPG图像本身已经是使用图像压缩技术处理过的，一般可压缩的内容较少，基本上大小已经不能再减多少

Answer 4

to hthunter(核桃-我的心在下雨,雨中我和她携手漫步) 其实采用clMax参数进行压缩，压缩率提高不了多少，反倒是压缩耗时却差别相当大，建议还是采用clDefault,必须时采用clFast就足够了。

Answer 5

嘻嘻，不过偶用措施也算是比较强硬，因为clNone其实上没用，所以偶通常把它给屏蔽掉，即只给出1、2、3三个选项,例:
'=================================================================================
'压缩选项
Public Enum ZlibCompressionLevel
       ZLIB_CompressionLevel_Fastest = 1 '最快压缩,速度最快,压缩率最低
       ZLIB_CompressionLevel_Default = 2 '默认压缩,速度一般,压缩率相当
       ZLIB_CompressionLevel_Max = 3     '最大压缩,速度最慢,压缩率最高
End Enum