function _parsepngstream($f, $file)
{
// Check signature
if ($this->_readstream($f, 8) != chr(137) . 'PNG' . chr(13) . chr(10) . chr(26) . chr(10)) {
$this->Error('Not a PNG file: ' . $file);
}
// Read header chunk
$this->_readstream($f, 4);
if ($this->_readstream($f, 4) != 'IHDR') {
$this->Error('Incorrect PNG file: ' . $file);
}
$w = $this->_readint($f);
$h = $this->_readint($f);
$bpc = ord($this->_readstream($f, 1));
if ($bpc > 8) {
$this->Error('16-bit depth not supported: ' . $file);
}
$ct = ord($this->_readstream($f, 1));
if ($ct == 0 || $ct == 4) {
$colspace = 'DeviceGray';
} elseif ($ct == 2 || $ct == 6) {
$colspace = 'DeviceRGB';
} elseif ($ct == 3) {
$colspace = 'Indexed';
} else {
$this->Error('Unknown color type: ' . $file);
}
if (ord($this->_readstream($f, 1)) != 0) {
$this->Error('Unknown compression method: ' . $file);
}
if (ord($this->_readstream($f, 1)) != 0) {
$this->Error('Unknown filter method: ' . $file);
}
if (ord($this->_readstream($f, 1)) != 0) {
$this->Error('Interlacing not supported: ' . $file);
}
$this->_readstream($f, 4);
$dp = '/Predictor 15 /Colors ' . ($colspace == 'DeviceRGB' ? 3 : 1) . ' /BitsPerComponent ' . $bpc . ' /Columns ' . $w;
// Scan chunks looking for palette, transparency and image data
$pal = '';
$trns = '';
$data = '';
do {
$n = $this->_readint($f);
$type = $this->_readstream($f, 4);
if ($type == 'PLTE') {
// Read palette
$pal = $this->_readstream($f, $n);
$this->_readstream($f, 4);
} elseif ($type == 'tRNS') {
// Read transparency info
$t = $this->_readstream($f, $n);
if ($ct == 0) {
$trns = array(ord(substr($t, 1, 1)));
} elseif ($ct == 2) {
$trns = array(ord(substr($t, 1, 1)), ord(substr($t, 3, 1)), ord(substr($t, 5, 1)));
} else {
$pos = strpos($t, chr(0));
if ($pos !== false) {
$trns = array($pos);
}
}
$this->_readstream($f, 4);
} elseif ($type == 'IDAT') {
// Read image data block
$data .= $this->_readstream($f, $n);
$this->_readstream($f, 4);
} elseif ($type == 'IEND') {
break;
} else {
$this->_readstream($f, $n + 4);
}
} while ($n);
if ($colspace == 'Indexed' && empty($pal)) {
$this->Error('Missing palette in ' . $file);
}
$info = array('w' => $w, 'h' => $h, 'cs' => $colspace, 'bpc' => $bpc, 'f' => 'FlateDecode', 'dp' => $dp, 'pal' => $pal, 'trns' => $trns);
if ($ct >= 4) {
// Extract alpha channel
if (!function_exists('gzuncompress')) {
$this->Error('Zlib not available, can\'t handle alpha channel: ' . $file);
}
$data = gzuncompress($data);
$color = '';
$alpha = '';
if ($ct == 4) {
// Gray image
$len = 2 * $w;
for ($i = 0; $i < $h; $i++) {
$pos = (1 + $len) * $i;
$color .= $data[$pos];
$alpha .= $data[$pos];
$line = substr($data, $pos + 1, $len);
$color .= preg_replace('/(.)./s', '$1', $line);
$alpha .= preg_replace('/.(.)/s', '$1', $line);
}
} else {
// RGB image
$len = 4 * $w;
for ($i = 0; $i < $h; $i++) {
$pos = (1 + $len) * $i;
$color .= $data[$pos];
$alpha .= $data[$pos];
$line = substr($data, $pos + 1, $len);
$color .= preg_replace('/(.{3})./s', '$1', $line);
$alpha .= preg_replace('/.{3}(.)/s', '$1', $line);
}
}
unset($data);
$data = gzcompress($color);
$info['smask'] = gzcompress($alpha);
if ($this->PDFVersion < '1.4') {
$this->PDFVersion = '1.4';
}
}
$info['data'] = $data;
return $info;
}