I'm learning <em>png</em> <em>IDAT</em> chunks now. I tried writing my own code to read them, and it works fine if there is only 1 <em>IDAT</em> chunk, but fails when there are more "<em>IDAT</em> 78 DA" chunks. My question is that: What should I modify in my code and how?
Thanks for all the replies. :)
<?php
$in_filename = "stego15.<em>png</em>";
$raw_data = file_get_contents($in_filename);
$idat_chunks = explode('<em>IDAT</em>', substr($raw_data, 0, -4));
foreach ($idat_chunks as $idat_number=>$idat_chunk) {
if ($idat_number==0) {
continue;
}
$chunk = substr($idat_chunk, 2, -4);
$decompressed = gzinflate($chunk);
list($width, $height) = getimagesize($in_filename);
$data = str_split(bin2hex($decompressed), $width*6+2);
$grouped_data = array();
foreach ($data as $row=>$d) {
$grouped_data[$row] = str_split(substr($d, 2), 6);
}
echo '<h1>'.$idat_number.'. chunk</h1>';
var_dump($grouped_data);
}
?>
