MagickContrastStretchImage() enhances the contrast of a color image by adjusting the pixels color to span the entire range of colors available. You can also reduce the influence of a particular channel with a gamma value of 0.
¯\_(ツ)_/¯
function contrastStretchImage($image_path, $black_point, $white_point, $channel)
{
$imagick = new \Imagick(realpath($image_path));
list ($width, $height) = array_values ($imagick->getImageGeometry ());
$imagick->contrastStretchImage(
$width * $height * $black_point / 100,
$width * $height * $white_point / 100,
$channel
);
header("Content-Type: image/jpeg");
echo $imagick->getImageBlob();
}