画面サイズ取得

// 画面取得
UIScreen *sc = [UIScreen mainScreen];
CGRect rect = sc.bounds;

// 画面サイズを取得してUIImage生成
UIImageView * imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,rect.size.width,rect.size.height)];

[self.view addSubview:imageView];