46

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

4

6 回答 6

42

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;
}
于 2009-01-06T09:39:45.903 回答
18

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:

imagecreatefromgifZeBadger 发表评论 #59787

于 2008-11-11T11:54:59.887 回答
7

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;
}
于 2008-11-11T12:18:36.923 回答
4

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;
}
于 2017-12-20T13:27:35.730 回答
2

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;
}
于 2017-02-12T18:27:36.857 回答
-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)

于 2013-08-30T04:19:38.403 回答