释放双眼，带上耳机，听听看~！
//_bgImageView是要放大的图片，ImageWidth、ImageHeight分别是_bgImageView原本的宽度和高度
-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
//滑动放大标签背景图片
[selfupdateImg];
}
//更新相册封面大小
- (void)updateImg {
CGFloat yOffset = self.tabelView.contentOffset.y;
if (yOffset < 0) {
CGFloat factor = ((ABS(yOffset) +ImageHeight) * ImageWidth) /ImageHeight;
CGRect f = CGRectMake( - (factor -ImageWidth) / 2,0,
factor, ImageHeight +ABS(yOffset));
_bgImageView.frame = f;
}else {
CGRect f = _bgImageView.frame;
f.origin.y = - yOffset;
_bgImageView.frame = f;
}
}