Sharpness function for GD to make images not so blurry after resize

sharpness.php

private function setSharpness($amount = 4)
{
	if ($amount < 0 || $amount > 100)
	{
		$amount = 4;
	}

	$min = $amount >= 10 ? $amount * -0.01 : 0;
	$max = $amount * -0.025;
	$abs = ((4 * $min + 4 * $max) * -1) + 1;
	$div = 1;


	$matrix = [
		[$min, $max, $min],
		[$max, $abs, $max],
		[$min, $max, $min]
	];

	imageconvolution($imageHandle, $matrix, $div, 0);

	return $this;
}