Masking With A Grayscale Image With PHP And ImageMagick - php

Question

I am trying to create a grayscale mask in Imagemagick (v7.0.11) that behaves like a layer mask in Photoshop where white areas are completely opaque and black areas are fully masked.
function grayscaleMaskTest () {
//Create a black and white mask
$mask = new Imagick();
$mask->newImage(300, 300, "#ffffff");
$mask->setImageType(IMAGICK::IMGTYPE_GRAYSCALE);
$mask->setImageFormat('gif');
//draw black circle
$draw = new ImagickDraw();
$draw->setStrokeWidth(1);
$draw->setStrokeOpacity(1);
$draw->setStrokeColor(new ImagickPixel("#000000"));
$draw->setFillColor(new ImagickPixel("#000000"));
$draw->circle(300/2, 300/2, 300/2, 300/2 + 100);
$mask->drawImage($draw);
//$mask->writeImage('C:\Users\Mike\Documents\images\mask.png'); //export mask
//Create final image
$final = new Imagick();
$final->newImage(300, 300, "#FF0000");
//Not sure if I had this right but tried writing the mask data to the alpha channel
//$final->compositeImage($mask, IMAGICK::COMPOSITE_COPYOPACITY, 0, 0, IMAGICK::CHANNEL_ALPHA);
$final->compositeImage($mask, IMAGICK::COMPOSITE_COPYOPACITY, 0, 0);
$final->writeImage('C:\Users\Mike\Documents\images\final.png');
}
The mask looks like this :
The desired result from this code if it worked would be this (minus the fake transparency) :

Answer 1

With help from #fmw42 this ended up working. Thanks!
//Create a black and white mask
$mask = new Imagick();
$mask->newImage(300, 300, "#ffffff");
//draw black circle
$draw = new ImagickDraw();
$draw->setStrokeWidth(1);
$draw->setStrokeOpacity(1);
$draw->setStrokeColor(new ImagickPixel("#0"));
$draw->setFillColor(new ImagickPixel("#0"));
$draw->circle(300/2, 300/2, 300/2, 300/2 + 100);
$mask->drawImage($draw);
$mask->setImageMatte(false); //<-------This got it going!
//Create final image
$final = new Imagick();
$final->newImage(300, 300, "#FF0000");
$final->compositeImage($mask, imagick::COMPOSITE_COPYOPACITY, 0, 0);`