Mask::createSharpen

static function createSharpen($precision)
{
	$mask = null;
	if($precision > 0)
	{
		$k = 1.0/((int)$precision);
		$mask = [
			[-$k, -$k, -$k],
			[-$k, 1+8*$k, -$k],
			[-$k, -$k, -$k],
		];
	}
	return new static($mask);
}