Jpeg to Bmp conversion takes unreasonable amount of time - delphi

Question

I have this function that takes 4.2 seconds to convert a jpg to bmp.
Why it takes so long? Can I make if faster?
IrfanView loads and converts the file in only a fraction of that time.
I thought that is spends most of the time in JPG.LoadFromFile. But when I measured the time I was surprised to see it spends most of the time in BMP.Assing(JPG).
function ConvertJPG2BMP(CONST FileName: string): TBitmap;
VAR JPG: TJpegImage;
begin
Result:= NIL;
JPG:= TJpegImage.Create;
TRY
JPG.LoadFromFile(FileName);
if (JPG.Width > 0) AND (JPG.Width < 32768)
AND (JPG.Height> 0) AND (JPG.Height < 32768) then
begin
Result:= TBitmap.Create;
TRY
Result.HandleType:= bmDIB;
// Fuji_FinePix_F550.JPG [3200x1800] [1.44MB]
Result.Assign(JPG); <--- 4 seconds!!
EXCEPT
FreeAndNil(Result);
END;
end;
FINALLY
FreeAndNil(JPG);
end;
end;

Answer 1

Since I wanted to test the slightly older functions once, it is a good opportunity to do this now.
The sources used are here
These have been changed a bit in the code below.
Somewhat adapted source code of OP's function ConvertJPG2BMP() (2512 : ms)
function ConvertJPG2BMP(CONST FileName: string): TBitmap;
VAR
JPG: TJpegImage;
begin
Result:= NIL;
JPG:= TJpegImage.Create;
TRY
JPG.LoadFromFile(FileName);
if (JPG.Width > 0) AND (JPG.Width < 32768)
AND (JPG.Height> 0) AND (JPG.Height < 32768) then
begin
Result:= TBitmap.Create;
TRY
Result.PixelFormat := pf24bit;
Result.Width := JPG.Width;
Result.Height := JPG.Height;
Result.HandleType:= bmDIB;
// 2018-10-17 14.04.23.jpg [2560x1920] [1.66MB]
Result.Assign(JPG);
Result.SaveToFile('F:\ProgramFiles\Embarcadero\dtx\Projects\Bmp-DIB\JPG2BMP.bmp');
EXCEPT
FreeAndNil(Result);
END;
end;
FINALLY
FreeAndNil(JPG);
end;
end;
The source for the TWICImage usage (296 : ms)
There is another class in Vcl.Graphics? called TWICImage that handles images supported by the Microsoft Imaging Component
Including BMP, GIF, ICO, JPEG, PNG, TIF and Windows Media Photo
procedure LoadImageFromStream(Stream: TStream; Image: TImage);
var
wic: TWICImage;
Bitmap: TBitmap;
begin
Stream.Position := 0;
wic := TWICImage.Create;
try
wic.LoadFromStream(Stream);
Image.Picture.Assign(wic);
Bitmap := TBitmap.Create;
try
Bitmap.PixelFormat := pf24bit;
Bitmap.Width := Image.Picture.Width;
Bitmap.Height := Image.Picture.Height;
Bitmap.Canvas.Draw(0, 0, Image.Picture.Graphic);
Bitmap.SaveToFile('F:\ProgramFiles\Embarcadero\dtx\Projects\Bmp-DIB\TWICImage.bmp');
finally
Bitmap.Free;
end;
finally
wic.Free;
end;
end;
procedure RenderImage(const Filename: string);
var
fs: TFileStream;
begin
fs := TFileStream.Create(Filename, fmOpenRead);
try
LoadImageFromStream(fs, Form1.Image1);
finally
fs.Free;
end;
end;
GetTickCount for all tested routines.
procedure TForm1.Button1Click(Sender: TObject);
var
MyDIB : TBitmap;
loadStr : string;
XStart,Xend : LongWord;
begin
loadStr := 'F:\ProgramFiles\Embarcadero\dtx\Projects\Bmp-DIB\2018-10-17 14.04.23.jpg';
XStart := GetTickCount;
if RadioGroup1.ItemIndex = 0 then MyDIB := ConvertJPG2BMP(loadStr);// ConvertJPG2BMP()
if RadioGroup1.ItemIndex = 1 then TestBmp(loadStr);
if RadioGroup1.ItemIndex = 2 then RenderImage(loadStr);// TWICImage
if RadioGroup1.ItemIndex = 3 then GetOleGraphic(loadStr);
Xend := GetTickCount;
Label1.Caption := IntToStr(xEnd-XStart) + ' : MS' ;
end;
The generated images are identical to the file size only from the function GetOleGraphic() is a smaller file produced with a worse resolution?
here the source used for the GetOleGraphic()

Answer 2

Here is a compact version of WIC image loader posted by moskito-x above.
Please VOTE HIS answer not mine. My answer here is only to provide the compact version and some details.
{-----------------------------------------------
Uses TWICImage
Advantages:
8+ times faster than Delphi's JPG function
Works with: animated GIF, PNG, JPG
Drawbacks:
Fails with JPEG2K
No EXIF support
Platform dependent
-----------------------------------------------}
function LoadImageWic(CONST FileName: string): TBitmap;
VAR
wic: TWICImage;
begin
wic := TWICImage.Create;
TRY
wic.LoadFromFile(FileName);
Result := TBitmap.Create;
TRY
Result.Assign(wic);
EXCEPT
FreeAndNil(Result);
END;
FINALLY
FreeAndNil(wic);
END;
end;

Answer 3

Just try to decompress the jpeg using our Open Source SynGDIPlus unit.
We found it much faster than the Delphi built-in jpeg.pas unit.
The latest revision can be retrieved from github.
As an alternative, you may try to use our fast Jpeg decoder using SSE2 but it doesn't handle all kind of Jpegs, and it is for Win32 only.