Example

function setStrokeAlpha($strokeColor, $fillColor, $backgroundColor)
{
    $draw = new \ImagickDraw();

    $draw->setStrokeColor($strokeColor);
    $draw->setFillColor($fillColor);
    $draw->setStrokeWidth(4);
    $draw->line(100, 100, 400, 145);
    $draw->rectangle(100, 200, 225, 350);
    $draw->setStrokeOpacity(0.1);
    $draw->line(100, 120, 400, 165);
    $draw->rectangle(275, 200, 400, 350);

    $image = new \Imagick();
    $image->newImage(500, 400, $backgroundColor);
    $image->setImageFormat("png");

    $image->drawImage($draw);

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