const d = Dimensions.get("window")
backgroundImage: {
position: 'absolute'
flex: 1,
backgroundColor:'rgba(0,0,0,0.45)',
width: d.width,
height: d.height
}
<ImageBackground
source={require('../../assets/signinBG.jpg')}
style={styles.backgroundImage}
resizeMode="repeat" // or contain or cover
>