JPG转换成BMP不成功？？？

procedure TForm14.Button2Click(Sender: TObject);
var
  i:TBitmap;
  j:TjpegImage;
begin

  form14.SavePictureDialog1.DefaultExt:='jpg';//'.jpg';
  //set the default file ext
  i:=TBitmap.Create;
  j:=TjpegImage.Create;

  i.LoadFromFile(form14.OpenPictureDialog1.FileName);
  j.Assign(i);
  if form14.SavePictureDialog1.Execute then
    j.SaveToFile(form14.SavePictureDialog1.FileName);

  i.Free;
  j.Free;
 { }
end;

//此段为JPG转换为BMP，但转换后保存的文件仍是JPG文件哦？？？？？？？？？？？？？？？？？

procedure TForm14.Button3Click(Sender: TObject);
var
  i:TBitmap;
  j:TjpegImage;
begin

form14.SavePictureDialog1.DefaultExt:='bmp';
  i:=TBitmap.Create;
  j:=TjpegImage.Create;

  j.LoadFromFile(form14.OpenPictureDialog1.FileName);
  i.Assign(j);
  if form14.SavePictureDialog1.Execute then
    j.SaveToFile(form14.SavePictureDialog1.filename);

  i.Free;
  j.Free;

end;