WIA's ShowAcquireImage only saves in BMP?

 //...
 uses   ComObj, WIA_TLB,   
 //...
procedure TMainForm.ScanWiaDocument(DocumentRef: String);
const
   wiaFormatJPEG = '{B96B3CAE-0728-11D3-9D7B-0000F81EF32E}';
   wiaFormatPNG  = '{B96B3CAF-0728-11D3-9D7B-0000F81EF32E}';
var
   CommonDlg: ICommonDialog;
   AImage: IImageFile;
   ImagePath: String;
begin
   CommonDlg := CreateOleObject('WIA.CommonDialog') as ICommonDialog;
   //Transfer as JPG
   try try
      AImage := CommonDlg.ShowAcquireImage(ScannerDeviceType,
                ColorIntent,    //or UnspecifiedIntent, GrayscaleIntent, TextIntent
                MinimizeSize,   //or MaximizeQuality
                wiaFormatJPEG,  //image format  **<----Only saves in BMP format!**!
                False,          //AlwaysSelectDevice
                False,          //UseCommonUI
                True);          //CancelError
      //Save the image
      ImagePath := 'C:\temp\scanimage\'+DocumentRef+'.'+ AImage.FileExtension;
      AImage.SaveFile(ImagePath);
   except
       on E:Exception do LogException(E, 'ScanWiaDocument', True);
   end;
   finally  //release interface
      CommonDlg := nil;
      AImage    := nil;
   end;
end;