Creating opacity for row’s background image

I have an image as the background of the row. I want to change the background image’s opacity, so the text is easier to read.

so far I’ve got

 background-opacity {
    opacity: 0.4;
    filter: alpha(opacity=40);
} 

But this changes all the row’s content opacity.

Any way to do this?

I got the idea from your hero widget and how you can control the opacity there, but can’t figure it out for the background of a row.