php - 如何从 PHP 读取 PNG 元数据？

Question

这是我目前所拥有的:

<?php

$file = "18201010338AM16390621000846.png";

$test = file_get_contents($file, FILE_BINARY);

echo str_replace("\n","<br>",$test);

?>

输出有点像我想要的，但我真的只需要第 3-7 行(含)。这就是现在的输出:http://silentnoobs.com/pbss/collector/test.php .我正在尝试将数据从“PunkBuster Screenshot (±) AAO Bridge Crossing”获取到“Resulting: w=394 X h=196 sample=2”。我认为通读文件并将每一行存储在一个数组中是相当直接的，行 [0] 需要是“PunkBuster Screenshot (±) AAO Bridge Crossing”，等等。所有这些行都可能发生变化，所以我不能只搜索有限的东西。

我已经尝试了几天了，但我的 php 水平很差，这并没有多大帮助。

Answer 1

PNG file format定义将 PNG 文档拆分为多个数据 block 。因此，您必须导航到您想要的 block 。

您要提取的数据似乎是在 tEXt block 中定义的。我编写了以下类以允许您从 PNG 文件中提取 block 。

class PNG_Reader
{
    private $_chunks;
    private $_fp;

    function __construct($file) {
        if (!file_exists($file)) {
            throw new Exception('File does not exist');
        }

        $this->_chunks = array ();

        // Open the file
        $this->_fp = fopen($file, 'r');

        if (!$this->_fp)
            throw new Exception('Unable to open file');

        // Read the magic bytes and verify
        $header = fread($this->_fp, 8);

        if ($header != "\x89PNG\x0d\x0a\x1a\x0a")
            throw new Exception('Is not a valid PNG image');

        // Loop through the chunks. Byte 0-3 is length, Byte 4-7 is type
        $chunkHeader = fread($this->_fp, 8);

        while ($chunkHeader) {
            // Extract length and type from binary data
            $chunk = @unpack('Nsize/a4type', $chunkHeader);

            // Store position into internal array
            if ($this->_chunks[$chunk['type']] === null)
                $this->_chunks[$chunk['type']] = array ();
            $this->_chunks[$chunk['type']][] = array (
                'offset' => ftell($this->_fp),
                'size' => $chunk['size']
            );

            // Skip to next chunk (over body and CRC)
            fseek($this->_fp, $chunk['size'] + 4, SEEK_CUR);

            // Read next chunk header
            $chunkHeader = fread($this->_fp, 8);
        }
    }

    function __destruct() { fclose($this->_fp); }

    // Returns all chunks of said type
    public function get_chunks($type) {
        if ($this->_chunks[$type] === null)
            return null;

        $chunks = array ();

        foreach ($this->_chunks[$type] as $chunk) {
            if ($chunk['size'] > 0) {
                fseek($this->_fp, $chunk['offset'], SEEK_SET);
                $chunks[] = fread($this->_fp, $chunk['size']);
            } else {
                $chunks[] = '';
            }
        }

        return $chunks;
    }
}

你可以这样使用它来提取你想要的 tEXt block :

$file = '18201010338AM16390621000846.png';
$png = new PNG_Reader($file);

$rawTextData = $png->get_chunks('tEXt');

$metadata = array();

foreach($rawTextData as $data) {
   $sections = explode("\0", $data);

   if($sections > 1) {
       $key = array_shift($sections);
       $metadata[$key] = implode("\0", $sections);
   } else {
       $metadata[] = $data;
   }
}