Suppress Warnings From libpng

Description

PNG files exported from some applications, most notably Photoshop, are written with an sRGB profile that libpng sees as invalid. Any attempt to load a file like this using the GD library causes a warning to be written to the PHP error log. It is not possible to suppress this warning.

The following code:

<?php
$image = imagecreatefrompng('clouds.png');

Results in this warning:

Warning: imagecreatefrompng(): gd-png: libpng warning: iCCP: known incorrect sRGB profile

Please see the attached file as an example of one that has the issue.

The only solution I have found so far is to post-process the PNG to remove the sRGB profile. This is not ideal for workflow with large numbers of files. Whilst it is possible to disable all warnings, they are often on in production so this is not a desirable solution.

I would like a method to suppress all libpng warnings. This could be implemented as a gd_ prefixed method that takes an optional bool parameter to toggle warnings on or off. If no parameter is passed it could return the current state.

首先定位 imagecreatefrompng 背后的 GD 实现及其对 libpng 警告的处理。检查现有 PHP GD API 如何公开图像加载行为，以及相关测试是否覆盖警告。完成标准是提供所请求的切换 libpng 警告的方式，包括可选的状态查询，并为提供的无效 profile 情况添加覆盖。