Performance Issue Loading JPEG
lazarus / 39-Graphics

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MaartenJB · 2011-06-09 12:00

Hi,

I've got a performance issue with loading large(r) jpeg foto's. I want
to show a preview of a JPEG image, but the way I'm using now is very
slow. In Delphi I can use the "TJpegImage.Scale" option, this is very
fast, but I can't find a similar function in Lazarus.

In lazarus 4mb jpg takes +/- 2.5 sec
Code: [Select]var
  myImage: TBGRABitmap;
begin
  myImage := TBGRABitmap.Create;
  try
    myImage.LoadFromFile('C:\temp\test.jpg');  // 4mb jpg, 2.5sec
    myImage.Draw(Image1.Canvas,Rect(0,0,Image1.Width,Image1.Height),Fa
lse);
  finally
    myImage.Free;
  end;
end;


In Delphi same image takes 140 MilliSec. (almost 20 times faster)
Code: [Select]var
  AJpg: TJpegImage;
begin
  AJpg := TJpegImage.Create;
  try
    AJpg.LoadFromFile('C:\temp\test.jpg'); //4mb,140millisec
    AJpg.Scale := jsEighth;
    Image1.Picture.Bitmap.Assign(AJpg);
  finally
    AJpg.Free;
  end;

I've tried a lot of things, browsed almost every web page, but can't
find a solution, I hope somebody else does....

Thanks in advance

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eny · 2011-06-09 15:08

Code: Delphi  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
myImage.LoadFromFile('C:\temp\test.jpg');  // 4mb jpg, 2.5sec0,9s on
my config.
Maybe Delphi cheats by initially just loading the raw data and not
doing any processing.

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MaartenJB · 2011-06-09 15:33

delphi needs to decompress the whole jpg first, before it's able to
draw the whole picture right?

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felipemdc · 2011-06-09 15:48

There was a fix in Free Pascal recently which could speed up image
loading. In this case you would need to try a snapshot containing the
latest fpc 2.5.1

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eny · 2011-06-09 17:49

Quote from: MaartenJB on June 09, 2011, 05:33:09 pmdelphi needs to
decompress the whole jpg first, before it's able to draw the whole
picture right?Sure, but is this done during the load process (which
apparently takes only 140ms) or just in time before the image is
drawn?

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MaartenJB · 2011-06-09 17:59

within the 140ms the jpg is loaded from file and drawn on the canvas.

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eny · 2011-06-09 19:52

Quote from: MaartenJB on June 09, 2011, 07:59:15 pmwithin the 140ms
the jpg is loaded from file and drawn on the canvas.

Did you verify this in the Delphi source code?
Did a small test myself: indeed Delphi is pretty fast!

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Leledumbo · 2011-06-09 23:13

I remember a posting in FPC forum / mailing list regarding palette
that's created by default. The svn fix disables this by default.

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theo · 2011-06-10 08:33

I've submitted a patch to enable scaling in fpreadjpeg:
http://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/packages/fcl-
image/src/fpreadjpeg.pas?r1=13963&r2=15855&sortby=date

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MaartenJB · 2011-06-11 11:08

@Theo;  Great stuff!  Thanks Theo, it works like a charm!

It took a while since I never worked with svn, and never compiled
fpc/lazarus before.

@All;  Thanks for the reply's!

Code: [Select]var
  myImage : TFPMemoryImage;
  myImgReader: TFPReaderJpeg;
begin
  myImage  :=  TFPMemoryImage.create(0, 0);
  myImgReader := TFPReaderJPEG.Create;
  try
    myImage.UsePalette := False;
    myImgReader.Scale:= jsEighth;

    myImage.LoadFromFile('C:\Documents and Settings\Administrator\My
Documents\Lazarus\foto\dsc_9537.jpg', myImgReader);
    Image1.Picture.Assign(myImage);
  finally
    myImage.Free;
    myImgReader.Free;
  end;
end;