delphi - 无法压缩 JPEG 图像并将其显示在屏幕上

Question

我尝试在imgQInput(这是一个TImage)中加载图像，将其分配给TJpegImage，压缩它(压缩因子5)并在imgQOutput(另一个TImage)中显示它。但这不起作用。 imgQOutput 中的图像与原始图像相同。由于压缩因素，它看起来应该非常像素化!然而，压缩是有效的，因为当我将 JPEG 保存到磁盘时，它非常小。

  JPG:= TJPEGImage.Create;
   TRY
     JPG.CompressionQuality:= trkQuality.Position;
     JPG.Assign(imgQInput.Picture.Graphic);
     CompressJpeg(JPG);
     imgQOutput.Picture.Assign(JPG);          <--------- something wrong here. the shown image is not the compressed image but the original one
   FINALLY
     FreeAndNil(JPG);
   END;


function CompressJpeg(OutJPG: TJPEGImage): Integer;
VAR tmpQStream: TMemoryStream;
begin
 tmpQStream:= TMemoryStream.Create;
 TRY
   OutJPG.Compress;
   OutJPG.SaveToStream(tmpQStream);
   OutJPG.SaveToFile('c:\CompTest.jpg');       <--------------- this works
   Result:= tmpQStream.Size;
 FINALLY
   FreeAndNil(tmpQStream);
 END;
end;

Answer 1

您根本没有使用压缩的 JPG。

将 CompressJpeg 更改如下:

function CompressJpeg(OutJPG: TJPEGImage): Integer;
VAR tmpQStream: TMemoryStream;
begin
 tmpQStream:= TMemoryStream.Create;
 TRY
   OutJPG.Compress;
   OutJPG.SaveToStream(tmpQStream);
   OutJPG.SaveToFile('c:\CompTest.jpg');    // You can remove this line.
   tmpQStream.Position := 0;                //
   OutJPG.LoadFromStream(tmpQStream);       // Reload the jpeg stream to OutJPG
   Result:= tmpQStream.Size;
 FINALLY
   FreeAndNil(tmpQStream);
 END;
end;