Save TBitmap image to Jpeg format image in Delphi

unit jpeg;

procedure BitmapToJpeg(FileName: string; Img:TGraphic);
var
  m_jpeg: TJpegImage;
  m_bitmap: TBitmap;
begin
  try
    m_jpeg:= TJpegImage.Create;

    m_bitmap := TBitmap.Create;
    m_bitmap.Width := Img.Width;
    m_bitmap.Height := Img.Height;
    m_bitmap.Canvas.Draw( 0, 0, Img);
//    m_bitmap.Canvas.StretchDraw( 0, 0, , ...,Img);

    m_jpeg.Assign( m_bitmap);

    m_jpeg.SaveToFile( FileName);
  finally
    m_jpeg.Free;
  end;
end;