Example

function tintImage($r, $g, $b, $a)
{
    $a = $a / 100;

    $imagick = new \Imagick();
    $imagick->newPseudoImage(400, 400, 'gradient:black-white');

    $tint = new \ImagickPixel("rgb($r, $g, $b)");
    $opacity = new \ImagickPixel("rgba(".(255 *$a*100).", $g, $b, $a)");
    
    
    $imagick->tintImage($tint, $opacity);
    $imagick->setImageFormat('png');
    
    $draw = new \ImagickDraw();
    $draw->setStrokeColor('black');
    $draw->setFillColor('white');
 
    $draw->setStrokeWidth(1);
    $draw->setFontSize(48);
    $draw->setStrokeAntialias(true);
    $draw->setFont("../fonts/Arial.ttf");
    
    $imagick->annotateImage($draw, 50, 50, 0, "Alpha is $a");
    header("Content-Type: image/png");
    echo $imagick->getImageBlob();
}