我目前在使用 GD 调整图像大小时遇到了一些问题。
一切正常,直到我想调整动画 gif 的大小,它在黑色背景上提供第一帧。
我试过使用getimagesize
,但这只给了我尺寸,没有任何东西可以区分任何 gif 和动画。
动画 gif 不需要实际调整大小,只需能够跳过它们就足以满足我们的目的。
有什么线索吗?
PS。我无权访问 imagemagick。
亲切的问候,
克里斯
在寻找相同问题的解决方案时,我注意到 php.net 站点对 Davide 和 Kris 所指的代码进行了后续跟进,但根据作者的说法,内存密集度较低,磁盘密集度可能较低.
我将在这里复制它,因为它可能很有趣。
来源:http ://www.php.net/manual/en/function.imagecreatefromgif.php#88005
function is_ani($filename) {
if(!($fh = @fopen($filename, 'rb')))
return false;
$count = 0;
//an animated gif contains multiple "frames", with each frame having a
//header made up of:
// * a static 4-byte sequence (\x00\x21\xF9\x04)
// * 4 variable bytes
// * a static 2-byte sequence (\x00\x2C)
// We read through the file til we reach the end of the file, or we've found
// at least 2 frame headers
while(!feof($fh) && $count < 2) {
$chunk = fread($fh, 1024 * 100); //read 100kb at a time
$count += preg_match_all('#\x00\x21\xF9\x04.{4}\x00[\x2C\x21]#s', $chunk, $matches);
}
fclose($fh);
return $count > 1;
}
该函数的 PHP 手册页中有一段简短的代码片段imagecreatefromgif()
,应该是您需要的:
这是工作功能:
/**
* Thanks to ZeBadger for original example, and Davide Gualano for pointing me to it
* Original at http://it.php.net/manual/en/function.imagecreatefromgif.php#59787
**/
function is_animated_gif( $filename )
{
$raw = file_get_contents( $filename );
$offset = 0;
$frames = 0;
while ($frames < 2)
{
$where1 = strpos($raw, "\x00\x21\xF9\x04", $offset);
if ( $where1 === false )
{
break;
}
else
{
$offset = $where1 + 1;
$where2 = strpos( $raw, "\x00\x2C", $offset );
if ( $where2 === false )
{
break;
}
else
{
if ( $where1 + 8 == $where2 )
{
$frames ++;
}
$offset = $where2 + 1;
}
}
}
return $frames > 1;
}
这是对当前投票最多的答案的改进,但我还没有足够的声誉发表评论。该答案的问题在于它以 100Kb 块读取文件,并且帧结束标记可能被分成 2 个块。解决方法是将前一帧的最后 20b 添加到下一帧:
<?php
function is_ani($filename) {
if(!($fh = @fopen($filename, 'rb')))
return false;
$count = 0;
//an animated gif contains multiple "frames", with each frame having a
//header made up of:
// * a static 4-byte sequence (\x00\x21\xF9\x04)
// * 4 variable bytes
// * a static 2-byte sequence (\x00\x2C) (some variants may use \x00\x21 ?)
// We read through the file til we reach the end of the file, or we've found
// at least 2 frame headers
$chunk = false;
while(!feof($fh) && $count < 2) {
//add the last 20 characters from the previous string, to make sure the searched pattern is not split.
$chunk = ($chunk ? substr($chunk, -20) : "") . fread($fh, 1024 * 100); //read 100kb at a time
$count += preg_match_all('#\x00\x21\xF9\x04.{4}\x00(\x2C|\x21)#s', $chunk, $matches);
}
fclose($fh);
return $count > 1;
}
如果给定文件太大,读取整个文件file_get_contents
可能会占用太多内存。我重构了之前给出的函数,它读取足够的字节来检查帧,并在找到至少 2 个帧后立即返回。
<?php
/**
* Detects animated GIF from given file pointer resource or filename.
*
* @param resource|string $file File pointer resource or filename
* @return bool
*/
function is_animated_gif($file)
{
$fp = null;
if (is_string($file)) {
$fp = fopen($file, "rb");
} else {
$fp = $file;
/* Make sure that we are at the beginning of the file */
fseek($fp, 0);
}
if (fread($fp, 3) !== "GIF") {
fclose($fp);
return false;
}
$frames = 0;
while (!feof($fp) && $frames < 2) {
if (fread($fp, 1) === "\x00") {
/* Some of the animated GIFs do not contain graphic control extension (starts with 21 f9) */
if (fread($fp, 1) === "\x2c" || fread($fp, 2) === "\x21\xf9") {
$frames++;
}
}
}
fclose($fp);
return $frames > 1;
}
动画 GIF 必须具有以下字符串
"\x21\xFF\x0B\x4E\x45\x54\x53\x43\x41\x50\x45\x32\x2E\x30"
我已经测试了一些动画 gif,似乎字符串位于文件的 pos 781 处(使用 file_get_contents 和 strpos 找到)