转载学习：tabbleView顶部图片的拉伸效果，

_heroBigImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"hero_bg.jpg"]];
    _heroBigImageView.frame = CGRectMake(0, -150, 320, 150);
//还要设置

       contentMode = UIViewContentModeScaleAspectFill;

        .clipsToBounds = YES;

[_tableView addSubview:_heroBigImageView];

2 设置tableview的contentInset，向下移动150
_tableView.contentInset = UIEdgeInsetsMake(150, 0, 0, 0);

3 scrollview的代理，获取contentoffset，然后从新设置imageview的frame
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    //获取当前活动的tableview
    CGFloat  y = scrollView.contentOffset.y;
    if (scrollView == _tableView) {
        if (y < -150) {
            CGRect frame = _heroBigImageView.frame;
            frame.size.height =  - y ;
            frame.origin.y = y;
            _heroBigImageView.frame = frame;
        }
    }
}