protected function unfilter(ByteArray $ba, $width, $height, $bpp)
{
$i = 0;
for ($y = 0; $y < $height; $y++) {
switch ($ba[$i++]) {
case 0:
$i += $width * $bpp;
break;
case 1:
foreach (range(0, $width * $bpp - 1) as $x) {
if ($x - $bpp >= 0) {
$ba->offsetSet($i, $ba->offsetGet($i) + $ba->offsetGet($i - $bpp) & 0xff);
}
$i++;
}
break;
case 2:
for ($x = 0; $x < $width * $bpp; $x++) {
if ($y > 0) {
$ba->offsetSet($i, $ba->offsetGet($i) + $ba->offsetGet($i - $width * $bpp - 1) & 0xff);
}
$i++;
}
break;
case 3:
for ($x = 0; $x < $width * $bpp; $x++) {
$left = $x - $bpp >= 0 ? $ba->offsetGet($i - $bpp) : 0;
$above = $y - 1 >= 0 ? $ba->offsetGet($i - $width * $bpp - 1) : 0;
$ba->offsetSet($i, $ba->offsetGet($i) + floor(($left + $above) / 2) & 0xff);
$i++;
}
break;
case 4:
for ($x = 0; $x < $width * $bpp; $x++) {
$left = $x - $bpp >= 0 ? $ba->offsetGet($i - $bpp) : 0;
$above = $y > 0 ? $ba->offsetGet($i - $width * $bpp - 1) : 0;
$upper_left = $x - $bpp >= 0 && $y > 0 ? $ba->offsetGet($i - $width * $bpp - 1 - $bpp) : 0;
$ba->offsetSet($i, $ba->offsetGet($i) + $this->paethPredictor($left, $above, $upper_left) & 0xff);
$i++;
}
break;
default:
throw new PNGDecodeException('未知のフィルタです。');
}
}
}
