Example

function transparentPaintImage($color, $alpha, $fuzz, $inverse)
{
    $imagick = new \Imagick(realpath("images/BlueScreen.jpg"));

    //Need to be in a format that supports transparency
    $imagick->setimageformat('png');

    $imagick->transparentPaintImage(
        $color,
        $alpha,
        $fuzz * \Imagick::getQuantum(),
        $inverse
    );

    //Not required, but helps tidy up left over pixels
    $imagick->despeckleimage();
    
    $canvas = new Imagick();
    $canvas->newPseudoImage(
        $imagick->getImageWidth(),
        $imagick->getImageHeight(),
        "pattern:checkerboard"
    );
    
    $canvas->compositeimage($imagick, \Imagick::COMPOSITE_ATOP, 0, 0);
    $canvas->setImageFormat('png');

    header("Content-Type: image/png");
    echo $canvas->getImageBlob();
}