问题 单项选择题

假设有一台摄像机,它的扫描速率为450行/帧×520像素/行×25帧/秒,图像子采样格式为4:2:0。为节省存储空间,如果每个Y信号量化为8位每样本,而Cr和Cb信号量化为6位每样本。存储10分钟这样的视像(video)至少需要多少()的磁盘容量(1GB=1024×1024×1024字节)。

A.9.8GB

B.4.9GB

C.4.5GB

D.其他数值

答案

参考答案:C

解析:

在CCIR 601标准中,图像数字化的子采样格式有以下几种。

(1)4:4:4格式:这种采样格式实际上不是子采样格式,而是指在每条扫描线上每 4个连续的采样点取4个亮度Y样本、4个红色差Cr样本和4个蓝色差Cb样本,这就相当于每个像素用3个样本表示。

(2)4:2:2格式:这种子采样格式是指在每条扫描线上每4个连续的采样点取4个亮度Y样本、2个红色差Cr样本和2个蓝色差Cb样本,平均每个像素用2个样本表示。

(3)4:1:1格式:这种子采样格式是指在每条扫描线上每4个连续的采样点取4个亮度Y样本、1个红色差Cr样本和1个蓝色差Cb样本,平均每个像素用1.5个样本表示。

(4)4:2:0格式:这种子采样格式是指在水平和垂直方向上每2个连续的采样点上取2个亮度Y样本、1个红色差Cr样本和1个蓝色差Cb样本,平均每个像素用1.5个样本表示。

1GB=1024×1024×1024字节

①答案A:450×520×25×3×10×60=9.8(GB)

②答案B:450×520×25×1.5×10×60=4.9(GB)

③答案C:450×520×25×{(4×8+2×6)/4

多项选择题
阅读理解

Boys need friends, suffer when they don't believe they have any, and worry over the ups and downs of relationships. Many adults believe that somehow boys need friends less than girls do, in truth, though, no boy is an island; boys value their friends throughout childhood and adolescence and are happier and healthier when they have solid relationships with peers(同龄人).

Despite the common belief that girls are better at relationships, most boys consider their friends a very important part of their lives, and boys may actually be better at keeping friendships than girls are. A recent study of 10 to 15­year­old boys and girls found that girls' friendships are actually more fragile. Girls tend to say and do hurtful things to each other more frequently than boys, and girls are more hurt by the end of a friendship.

Boys are the living definition of the phrase “peer group”; they love games with rules, competition, and doing things together. Boys seem to enjoy, even need the opportunity to test themselves against others, and many lasting friendships begin in karate(空手道) class or on the basketball court. Competence and skill are widely respected; being picked last for a team or left out altogether is an experience that can haunt(萦绕心头) a boy for years.

As boys mature(成熟), the friendship becomes even more important, and it frequently widens to include girls. During the teen years, friends can become the most important part of a boy's life—and a part in which his parents are not included. The confusion of being a teenager leads boys to form close bonds(关系) with friends. There is the sense for many boys that a friend is someone who is “always there for me”, someone he can trust. They may be partners in crime or partners in study, but the friendship of adolescent boys can run surprisingly deep.

小题1:The common belief of adults is that boys________.

A.don't care about others as much as girls

B.don't value friendship as much as girls

C.have the same friendship as girls

D.have healthier friendship than girls小题2:According to the text, boys' friendship________.

A.is usually built around active play

B.tends to be in small groups

C.can bear mutual hurt between friends

D.doesn't suffer from failure小题3:The author mentions the study in the second paragraph to prove ________.

A.many people believe girls are better at relationships

B.most boys consider their friends very important

C.boys may be better at keeping friendships than girls

D.boys may be more active in a friendship小题4:As a boy gets older, he tends to________.

A.widen his circle of friends to include different kinds of people

B.shift his focus from his friends to himself

C.leave his parents out of his friendship

D.be confused about what a friendship is小题5:What's the best title for the text?

A.Friendships between Boys and Girls

B.Boys and Their Friendship

C.Childhood and Adolescent Friendship

D.Tips on Making Friends with Boys