public function Threshold(&$gdimg, $cutoff)
{
$width = ImageSX($gdimg);
$height = ImageSY($gdimg);
$cutoff = min(255, max(0, $cutoff ? $cutoff : 128));
for ($x = 0; $x < $width; $x++) {
for ($y = 0; $y < $height; $y++) {
$currentPixel = phpthumb_functions::GetPixelColor($gdimg, $x, $y);
$grayPixel = phpthumb_functions::GrayscalePixel($currentPixel);
if ($grayPixel['red'] < $cutoff) {
$newColor = phpthumb_functions::ImageColorAllocateAlphaSafe($gdimg, 0x0, 0x0, 0x0, $currentPixel['alpha']);
} else {
$newColor = phpthumb_functions::ImageColorAllocateAlphaSafe($gdimg, 0xff, 0xff, 0xff, $currentPixel['alpha']);
}
ImageSetPixel($gdimg, $x, $y, $newColor);
}
}
return true;
}
