我可以使用php和gd检测GIF动画吗？

Question

我目前遇到一些使用GD调整图像大小的问题.

一切正常,直到我想调整动画gif的大小,在黑色背景上提供第一帧.

我尝试过使用getimagesize但只给了我维度,没有什么可以区分任何gif和动画.

GIF动画不需要实际调整大小,只要能够跳过它们就足够了.

有线索吗？

PS.我无法访问imagemagick.

亲切的问候,

短剑的一种

Answer 1

在寻找同一问题的解决方案时,我注意到php.net网站对Davide和Kris所指的代码进行了跟进,但据作者称,内存密集程度较低,可能磁盘密集程度较低.

我会在这里复制它,因为它可能是有意义的.

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;
}

Answer 2

imagecreatefromgif()函数的PHP手册页中有一段简短的代码片段,应该是您需要的:

imagecreatefromgif 评论#59787由ZeBadger

Answer 3

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;
}

Answer 4

这是对当前投票最高的答案的改进，但我还没有足够的声誉来发表评论。该答案的问题在于，它以 100Kb 块的形式读取文件，并且帧标记的结尾可能会被分成 2 个块。解决这个问题的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;
}