imagecreatefrompng

(PHP 4, PHP 5, PHP 7, PHP 8)

imagecreatefrompng由文件或 URL 创建一个新图象。

说明

imagecreatefrompng(string $filename): GdImage|false

imagecreatefrompng() 返回图像标识符,代表从指定文件名获得的图像。

小技巧

如已启用fopen 包装器,在此函数中, URL 可作为文件名。关于如何指定文件名详见 fopen()。各种 wapper 的不同功能请参见 支持的协议和封装协议,注意其用法及其可提供的预定义变量。

参数

filename

PNG 图像的路径。

返回值

成功后返回图象对象,失败后返回 false

更新日志

版本 说明
8.0.0 成功时,此函数现在返回 GDImage 实例;之前返回 resource

示例

示例 #1 在加载 PNG 期间处理错误的示例

<?php
function LoadPNG($imgname)
{
/* Attempt to open */
$im = @imagecreatefrompng($imgname);

/* See if it failed */
if(!$im)
{
/* Create a blank image */
$im = imagecreatetruecolor(150, 30);
$bgc = imagecolorallocate($im, 255, 255, 255);
$tc = imagecolorallocate($im, 0, 0, 0);

imagefilledrectangle($im, 0, 0, 150, 30, $bgc);

/* Output an error message */
imagestring($im, 1, 5, 5, 'Error loading ' . $imgname, $tc);
}

return
$im;
}

header('Content-Type: image/png');

$img = LoadPNG('bogus.image');

imagepng($img);
imagedestroy($img);
?>

以上示例的输出类似于:

imagecreatefrompng() 示例
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User Contributed Notes 4 notes

up
83
Anonymous
20 years ago
If you're trying to load a translucent png-24 image but are finding an absence of transparency (like it's black), you need to enable alpha channel AND save the setting. I'm new to GD and it took me almost two hours to figure this out.

<?php
$imgPng
= imageCreateFromPng($strImagePath);
imageAlphaBlending($imgPng, true);
imageSaveAlpha($imgPng, true);

/* Output image to browser */
header("Content-type: image/png");
imagePng($imgPng);
?>
up
5
sageptr at gmail dot com
3 years ago
Because gd and imagick do not support animated PNG (at this moment), i wrote a simple function to determine if given PNG is APNG or not. It does not validate PNG, only checks whenever "acTL" chunk appears before "IDAT" like the specification says: https://wiki.mozilla.org/APNG_Specification

<?php

function is_apng(string $filename): bool
{
$f = new \SplFileObject($filename, 'rb');
$header = $f->fread(8);
if (
$header !== "\x89PNG\r\n\x1A\n") {
return
false;
}
while (!
$f->eof()) {
$bytes = $f->fread(4);
if (
strlen($bytes) < 4) {
return
false;
}
$length = unpack('N', $bytes)[1];
$chunkname = $f->fread(4);
switch (
$chunkname) {
case
'acTL':
return
true;
case
'IDAT':
return
false;
}
$f->fseek($length + 4, SEEK_CUR);
}
return
false;
}

?>
up
12
marcos at assl-site dot net
17 years ago
I had the same problem as jboyd1189 at yahoo dot com but I solve d it allocating more memory dynamically.

Usually the memory_limit var on php.ini is set to 8M. Unfortunately, the required amount of memory to manage a PNG image about 1000x1000 could be bigger !

The approach I used to solve the problem is:

1-Calculate the memory required by the image
2-Set the new memory_limit value
3-Create the PNG image and thumbnail
4-Restore the original value

1-The following value works for me:
$required_memory = Round($width * $height * $size['bits']);

Note that for JPEG the requirements are not the same:
http://es2.php.net/manual/en/function.imagecreatefromjpeg.php#60241

2-Use somthing like:
$new_limit=memory_get_usage() + $required_memory;
ini_set("memory_limit", $new_limit);

4-ini_restore ("memory_limit");
up
0
admin at wdfa dot co dot uk
15 years ago
When using imagecreatepng with alpha blending you will lose the blending.

To over come this use something like the following
<?php
$dstimage
=imagecreatetruecolor($width,$height);
$srcimage=imagecreatefrompng($src);
imagecopyresampled($dstimage,$srcimage,0,0,0,0, $width,$height,$width,$height);
?>
Where $width and $height are the width and height of the $src image.

This will create a true colour image then copy the png image to this true colour image and retain alpha blending.
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