PHP iOS PNG normalizer. This PHP class can be used to convert an iOS compressed PNG (CgBI format files) back to the standard format. Requires PHP 5.4 or greater. Credit goes to Axel E. Brzostowski for the original Python version of this script: http://www.axelbrz.com.ar/?mod=iphone-png-images-normalizer

iOSPNGNormalizer.php

<?php

class iOSPNGNormalizer
{
    public static function fix($filename, $destfilename = null)
    {
        try {
            $handle = fopen($filename, "rb");
            $oldPNG = fread($handle, filesize($filename));
            fclose($handle);

            $newPng = self::getNormalizedPNG($oldPNG);
            if (is_null($destfilename))
                $destfilename = $filename;

            file_put_contents($destfilename, $newPng);
        } catch (Exception $exc) {
            return $exc->getMessage();
        }
        return true;
    }

    public static function getNormalizedPNG($oldPNG)
    {
        // Check if the orginal png needs to be processed
        $im = @imagecreatefromstring($oldPNG);
        if($im !== false)
            return $oldPNG;
        
        $pngheader = "\x89PNG\r\n\x1a\n";

        if (substr($oldPNG, 0, 8) != $pngheader)
            return;

        $newPNG = substr($oldPNG, 0, 8);

        $chunkPos = 8;

        while ($chunkPos < strlen($oldPNG)) {
            // Reading chunk
            $chunkLength = unpack("N", substr($oldPNG, $chunkPos, $chunkPos + 4));
            $chunkLength = array_shift($chunkLength);
            $chunkType = substr($oldPNG, $chunkPos + 4, 4);
            $chunkData = substr($oldPNG, $chunkPos + 8, $chunkLength);
            $chunkCRC = unpack("N", substr($oldPNG, $chunkPos + $chunkLength + 8, 4));

            $chunkCRC = array_shift($chunkCRC);
            $chunkPos += $chunkLength + 12;

            // Reading header chunk
            if ($chunkType == 'IHDR') {
                $width = unpack("N", substr($chunkData, 0, 4));
                $width = array_shift($width);
                $height = unpack("N", substr($chunkData, 4, 8));
                $height = array_shift($height);
            }

            // Reading image chunk
            if ($chunkType == 'IDAT') {
                try {
                    // Uncompressing the image chunk
                    $bufSize = $width * $height * 4 + $height;
                    $chunkData = zlib_decode($chunkData, $bufSize);
                } catch (Exception $exc) {
                    return $oldPNG; // already optimized
                }

                // Swapping red & blue bytes for each pixel
                $newdata = "";
                for ($y = 0; $y < $height; $y++) {
                    $i = strlen($newdata);
                    $newdata .= $chunkData[$i];
                    for ($x = 0; $x < $width; $x++) {
                        $i = strlen($newdata);
                        $newdata .= $chunkData[$i + 2];
                        $newdata .= $chunkData[$i + 1];
                        $newdata .= $chunkData[$i + 0];
                        $newdata .= $chunkData[$i + 3];
                    }
                }

                // Compressing the image chunk
                $chunkData = $newdata;
                $chunkData = zlib_encode($chunkData, ZLIB_ENCODING_DEFLATE);

                $chunkLength = strlen($chunkData);
                $chunkCRC = crc32($chunkType . $chunkData);
                $chunkCRC = ($chunkCRC + 0x100000000) % 0x100000000;
            }

            if ($chunkType != 'CgBI') {
                $newPNG .= pack("N", $chunkLength);
                $newPNG .= $chunkType;
                if ($chunkLength > 0)
                    $newPNG .= $chunkData;
                $newPNG .= pack("N", $chunkCRC);
            }

            // Reading header chunk
            if ($chunkType == 'IEND') {
                break;
            }
        }

        return $newPNG;
    }

}