Question

I try to load an image in imgQInput (which is a TImage), assign it to a TJpegImage, compress it (compression factor 5) and show it in imgQOutput (another TImage). But it doesn’t work. The image in imgQOutput is the same as the original. It should look VERY pixelated because of the compression factor! The compression works however, because when I save the JPEG to disk it is really small.

  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

You did not used the compressed JPG at all.

Change CompressJpeg as followings:

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;