Imao put UIImageView on background is not the best idea . In my case i added on controller view other 2 views . First view has [UIColor clearColor]
on background, second - color which u want to be transparent (grey in my case).Note that order is important.Then for second view set alpha 0.5(alpha >=0 <=1).Added this to lines in prepareForSegue
infoVC.providesPresentationContextTransitionStyle = YES;
infoVC.definesPresentationContext = YES;
And thats all.