超越PHP - Exceed PHP: imagecreatefrompng

说明

resource imagecreatefrompng ( string filename)

imagecreatefrompng() 返回一图像标识符，代表了从给定的文件名取得的图像。

imagecreatefrompng() 在失败时返回一个空字符串，并且输出一条错误信息，不幸地在浏览器中显示为断链接。为减轻调试工作下面的例子会产生一个错误 PNG：
例子 1. 处理创建过程中的错误（courtesy vic at zymsys dot com）

<?php function LoadPNG ($imgname) { $im = @imagecreatefrompng ($imgname); /* Attempt to open */ if (!$im) { /* See if it failed */ $im = imagecreate (150, 30); /* Create a blank image */ $bgc = imagecolorallocate ($im, 255, 255, 255); $tc = imagecolorallocate ($im, 0, 0, 0); imagefilledrectangle ($im, 0, 0, 150, 30, $bgc); /* Output an errmsg */ imagestring ($im, 1, 5, 5, "Error loading $imgname", $tc); } return $im; } ?>

提示: 如果“fopen wrappers”已经被激活，则您在使用该函数的时候，可以把 URL 作为文件名来使用。请参阅 fopen() 获取怎样指定文件名的详细信息以及支持的 URL 协议的列表附录 L。

警告

Windows 版本的 PHP 在 4.3.0 版之前不支持该函数的远程文件访问，即使 allow_url_fopen 选项已被激活。

add a note User Contributed Notes
imagecreatefrompng

netfiend at mediaone dot net
24-May-2001 07:04

I've noticed a couple of things with the ImageCreateFromPng function that
may be useful if your having problems.  



1st thing I noticed is
that the PNG file you are creating from needs to be indexed and less than
256 colors.  



Secondly, you need to reduce the color depth by 1
for each color you plan on generating in php...  I.E.  if you plan on
drawing 50 different colors on the screen with php you need to allocate
space for them by reducing the origional image's color depth to 205 colors
(I was pulling my hair out on this one for a while because the wrong colors
were showing up in the output).  



Also, if you are saving the
image as a PNG you need to allocate the 1st color as white.. The reason for
this is that Internet Explorer seems to interpret the first color in an
indexed PNG as white no matter what color it is... (Figured this out when
all my pretty black text was turning up as white in I.E. and was normal in
Netscape; allocated the first color in the image as white and the problem
went away.) 



-- hope this helps.

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