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
<?php function LoadPNG($imgname) { $im = @imagecreatefrompng($imgname); /* Attempt to open */ if(!$im) { /* See if it failed */ $im = imagecreatetruecolor(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，则在本函数中可以把 URL 作为文件名来使用。请参阅 fopen() 函数来获取怎样指定文件名的详细信息以及支持 URL 封装协议的列表：附录 L。

警告

Windows 版本的 PHP 在 4.3.0 版之前不支持本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

jboyd1189 at yahoo dot com
06-Jul-2006 05:49


I was having a terrible time with the imagecreatefrompng function as it was working perfectly for one image and not at all for another.  After many hours of frustration, I discovered that the problem was the image size (number of pixels).  It appears that the maximum number of pixels this function will process is 1,040,000.  So, be sure that the pixel resolution of the image (eg. 1040 x 1000) does not exceed this value.

alext82 at hotmail dot com
31-May-2006 08:54


I was having trouble with 

$black = imagecolorallocate($im, 0, 0, 0);

, as it would always display grey letters.



this solved it however:



$black = imagecolorresolve($im, 0, 0, 0);



this regarding this function.



imagettftext($im, 11, 7, 55, 60, $black, $font, $string);



I hope this helps.

hendrikjan dot vanmeerveld at gmail dot com
01-May-2006 06:23


Another usefull note for those using ImageCreateFromPng:

PHP and GD do not recognize grayscale/alpha images.



So if you use grayscale images with transparency between 0% and 100%, then save the image as RGB.



At least this is true for PHP Version 4.4.2-1 and in 5.1.2-1 with pictures made with GIMP 2.2.8.

ketay [AT] comcast [DOT] net
05-Sep-2005 03:33


A correction... If you are to set it to FALSE, then not only does it add the transparency to wherever you put it, but it takes the transparency out of the TTF files. Setting it to TRUE however, keeps your transparency both in your PNG file, and in any TTF text you make apply to the image.

rf at i---i dot org
02-Nov-2004 07:47


***CORRECTION*** to 07-Jun-2004 01:14 

imageAlphaBlending must be false, NOT TRUE



$imgPng = imageCreateFromPng($strImagePath);

imageAlphaBlending($imgPng, false); <<<FALSE

imageSaveAlpha($imgPng, true);

07-Jun-2004 07:14


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); 

?>

csaba at alum dot mit dot edu
01-Jun-2004 01:57


This is a another case of someone (IE) thinking they know better than you what you want.  If you are of a mind to generate a complicated (read takes a long time) image incrementally, you might do it by having an IFRAME which calls to the image generating PHP script.  That munches for a bit, saves the file, returns to the client (remembering we're in the iframe so the user doesn't see all this) (with appropriate state information in <input type=hidden ...> fields) which kicks off an <body onLoad='docInit()' ...> whose purpose is to set the src attribute of the png image to the saved file (so the user sees the changes), and then resubmit the iframe (the image isn't in the iframe so the iframe can be hidden) to repeat the process.  Very nifty.



However, IE 6 has decided that it is far better to use a cached version of an image even on a local machine, where it can readily see that it changed, rather than to go to the source.  And, since it's a file, you can't so easily set headers on it.  This means that your incremental updates may not show any updates.



I solved this by (1) having Apache rewrite every .png request to a single .php file:

RewriteRule ^(.*).png$ pngPassThru.php?file=$1.png [QSA,L,NC]



(2) All pngPassThru.php does is to return the .png file with "don't cache me" headers.  Avoid leading/trailing spaces in pngPassThru.php.  The headers might be simplified - I've collected them from various sources and am not sure which ones could be eliminated.  But this is working for me on IE 6:

<?php

header("Content-type: image/png");

header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");

header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");

header("Cache-Control: no-store, no-cache, must-revalidate");

header("Cache-Control: post-check=0, pre-check=0", false);

header("Pragma: no-cache");

$file=@$_GET['file'];

$size= filesize($file); 

header("Content-Length: $size bytes"); 

readfile($file);

?>



Csaba Gabor

aniakovas at yahoo dot co dot uk
27-Apr-2004 09:13


Hey guys,



It has been my experience that the image type of a png file is best set to:-



image/x-png



This may be a peculiarity of the server I'm working on, which is running Apache/FreeBSD



Ania

polak_sg at hotmail dot com
05-Nov-2002 11:02


don't forget to write the header into your function file!!

header ("Content-type: image/png");

wyvern at greywyvern.com
05-Oct-2002 11:45


Make sure when coding image serving scripts that you avoid using the full "http://" URL of the image whenever possible.  Use "../imagename" etc.



Loading URL's from your own site will double your used bandwidth, as the script grabbing the image will count against it as well as sending it to the browser.

robross at comcast dot net
27-Feb-2002 08:47


This color table issue is actually a bit more complicated.



From my testing, it would appear that whatever colors you have specified in the color table for your picture in the first nth number of spots, those colors will automatically be given to the first "n" colors you attempt to use in your CreateImagefromPNG.



So, for example, if you need to create dynamic black and red text in your image, the first three spots in the color table for your background image should be white, black and red (in this order).



This can be a pain, but it is the only way to ensure that your images look as intended in all browsers.

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.

add a note