001+ PNG compression test:
001- PNG compression test: ok
002+ Warning: imagecreatefrompng(): '/root/lamp-project/php-tools/php-5.4.37/ext/gd/tests/test_pngcomp.png' is not a valid PNG file in %s/pngcomp.php on line 10
003+
004+ Warning: imagecolorat() expects parameter 1 to be resource, boolean given in %s/pngcomp.php on line 11