procedure TForm1.Button2Click(Sender: TObject);
var
  transColor: TRGB;
begin
  ImageEnView1.IO.LoadFromFile('D:\makestrans.bmp');

  // Bottom left pixel represents the transparent color
  transColor := ImageEnView1.IEBitmap.Pixels[0, Height-1];

  ImageEnView1.Proc.SetTransparentColors( transColor, transColor, 0 );

  ImageEnView1.IO.SaveToFile('D:\NowTransparent.png');
end;