procedure GetScreen(var Bmp: TBitmap);
var
Dc: HDC;
MyCanvas: TCanvas;
MyRect: TRect;
begin
Dc := GetWindowDC(0);
MyCanvas := TCanvas.Create;
try
MyCanvas.Handle := Dc;
MyRect:=Rect(0,0,Screen.Width, Screen.Height);
//图像为 24位真彩色，也可根据实际需要调整
Bmp.PixelFormat := pf24bit;
Bmp.Width := MyRect.Right;
Bmp.Height := MyRect.Bottom;
//捕捉整个屏幕图像
Bmp.Canvas.CopyRect(MyRect, MyCanvas, MyRect);
finally
MyCanvas.Handle := 0;
MyCanvas.Free;
ReleaseDC(0, Dc);
end;
end;

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;

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;

procedure TForm1.Button1Click(Sender: TObject);
var
Bmp: TBitmap;
CompressedStream: TMemoryStream;
begin
Bmp := TBitmap.Create;
CompressedStream := TMemoryStream.Create;
Try
//捕获当前整个屏幕 ,将图像保存至 Bmp对象中
GetScreen(Bmp);
//将 Bmp对象中的图像保存至内存流中
Bmp.SaveToStream(CompressedStream);
//按缺省的压缩比例对原始图像流进行压缩
CompressBitmap(CompressedStream, clMax);
//将压缩之后的图像流保存为自定义格式的文件
CompressedStream.SaveToFile('C:\cj.dat');
finally
Bmp.Free;
CompressedStream.Free;
end;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
CompressedStream: TFileStream;
Bmp: TBitmap;
begin
Bmp := TBitmap.Create;
//以文件流的只读方式打开自定义的压缩格式文件
CompressedStream := TFileStream.Create('C:\cj.dat' , fmOpenRead);
Try
//将被压缩的图像流进行解压缩
UnCompressBitmap(CompressedStream, Bmp);
//将原始图像流还原为指定的 BMP文件
Bmp.SaveToFile('C:\cj.bmp');
finally
Bmp.Free;
CompressedStream.Free;
end;
end;