reduce opacity of background image css

.img1 {
opacity: 0.6;
z-index=1;
}

img {
  opacity: 0.5;
} 

background-image: url(IMAGE_URL); /* fallback for older browsers */

background-image: linear-gradient(to bottom, rgba(0,0,0,0.6) 0%,rgba(0,0,0,0.6) 100%), url(IMAGE_URL);