Imagick: tiff to PNG8

gistfile1.php

<?php

header('Content-type: image/png');
$image = "/var/www/html/images/image.TIFF";

$im = new Imagick($image);
// resize by 500 width and keep the ratio
$im->thumbnailImage(500, 0);
//Set new image format 'PNG8'
$im->setImageFormat("PNG8");
//Get the min colors of the image.
$colors =min(255,$im->getImageColors());

$im->quantizeImage($colors,Imagick::COLORSPACE_RGB,0,false,false);
$im->setImageDepth(8);
echo $im;