3.3 Data Representation

Question 1

Pixel

Answer 1

The smallest element of a bitmap image that is only one colour.

Question 2

VDU

Answer 2

Visual display unit.
Monitor
Computer

Question 3

Resolution

Answer 3

The number of bits per area of an image.

Question 4

Pixilation

Answer 4

Occurs when the image is overstretched and the image will have a blocky and blurred appearance. This arises when the image is presented as too large a size and there are not enough pixels to reproduce the details in the image at this larger size.

Question 5

Bitmap size

Answer 5

Width in pixels X Height in pixels

Question 6

Colour depth

Answer 6

The number of bits used to indicate the colour of a single pixel.

Question 7

Bitmap file size

Answer 7

Width X Height X Colour depth

Question 8

Metadata

Answer 8

Metadata is data about data.
• File type
• Data created
• Height and width
• Resolution
• Colour depth

Question 9

What is sound?

Answer 9

Sound is analogue, this means it takes the form of a continuous wave that changes smoothly.

Question 10

Amplitude

Answer 10

How loud the sound is

Question 11

Frequency

Answer 11

How often the sound is measured.

Question 12

Analogue

Answer 12

Analogue sound are pure and of perfect quality.

Question 13

Sampling

Answer 13

To record a sound, the computer samples the sound at regular points. Then it converts the sample measurements into binary code.

Question 14

Bit rate

Answer 14

The number of bits stored per sample.

Question 15

Metadata

Answer 15

Information added to the sound.
• Author
• Album
• Track file

Question 16

MP3 files

Answer 16

Form of lossy compression that removes parts of the sound that are least likely to be noticed by the human ear.

Question 17

WAV files

Answer 17

WAV files are bigger than MP3 files because lossy compression is not applied to WAV files, this means that they are not as good for sharing as MP3s but are usually better quality.

Question 18

Sampling rate/frequency

Answer 18

The number of samples that are taken per second measured in Hz.

Question 19

Sample size

Answer 19

The number of bits allocated to each sample.

Question 20

File size

Answer 20

Sampling rate X Sample resolution X length

Question 21

Bit

Answer 21

A bit is one single binary digit.
A byte is 8 bits.

Question 22

Prefixes

Answer 22

Kilo, 1 kB is 1,000 bytes
Mega, 1MB is 1,000 kilobytes
Giga, 1GB is 1,000 Megabytes
Tera, 1TB is 1,000 Gigabytes

Question 23

Binary shifting

Answer 23

Left shifting by 1 = multiplication by 2
Right shifting by 1 = integer division by 2

Question 24

Binary shifting in general

Answer 24

Left shifting by n = multiplication by 2 to the power of n.
Right shifting by n = integer division by 2 to the power of n.

Question 25

Binary addition rules

Answer 25

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 10
1 + 1 + 1 = 11

Question 26

Character set

Answer 26

The group of symbols that a computer can represent and includes letters, digits, punctuation marks and control characters.

Question 27

ASCII

Answer 27

• 7-bit character set
• 128 different characters
• Represent letters of the English alphabet

Question 28

Unicode

Answer 28

• Uses up to 32 bits.
• Can be used to represent a wider range of characters and therefore other languages such as Chinese, and scientific symbols.

Question 29

Lossy compression

Answer 29

The reduction of bits, actually removing bits from a file. Can not be recovered. Some of the quality of the original file will be lost.

Question 30

Lossless compression

Answer 30

Shrinks the file down, but restores it to its original size and quality after. No loss of information.

Question 31

Why compress files?

Answer 31

• To make the files smaller.
• Less time/less bandwidth to transfer data.
• Takes up less space on the disk.

Question 32

Example of lossless compression

Answer 32

Run length encoding - sequences of the same values are stored in pairs of the value and the number of those values.

Question 33

Huffman coding

Answer 33

A from of compression that allows us to use fewer bits for higher frequency data. More common letters are represented using fewer bits than less common letters.