Darken CSS background image

Question

It ought to be a rather easy question. My website does what I say:

#landing-wrapper {
    display:table;
    width:100%;
    background:url('landingpagepic.jpg');
    background-position:center top;
    height:350px;
}

I want to make the backdrop picture darker. I don't believe I can actually add another div above it to darken it because this DIV has UI components. Suggestions?