Question

我目前遇到一些使用GD调整图像大小的问题。

一切正常，直到我想要调整动画gif的大小，在黑色背景上提供第一帧。

我尝试过使用getimagesize，但这只会给我尺寸，而不能区分任何gif和动画。

动画GIF不需要实际调整大小，只要能够跳过它们就足够了。

任何线索？

PS。我无法访问imagemagick。

亲切的问候，

克里斯

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，可能更少磁盘密集型。

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，应该是您所需要的：

imagecreatefromgif comment #59787 by ZeBadger

Answer 3

这是工作职能：

/**
 * 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

如果给定文件太大，使用file_get_contents读取整个文件可能会占用太多内存。我重新考虑了之前给出的函数，它只读取足够的字节来检查帧，并在找到至少2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;
}

Answer 5

这是对当前最高投票答案的改进，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，并且帧标记的末尾可能在2个块之间分割。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;
}

Answer 6

动画GIF必须包含以下字符串

"\x21\xFF\x0B\x4E\x45\x54\x53\x43\x41\x50\x45\x32\x2E\x30"

我已经测试了几个GIF动画，看起来字符串位于文件的pos 781（找到了file_get_contents和strpos）

我可以使用php和gd检测GIF动画吗？

6 个答案: