digital data encoding

Question 1

what do computers run on?

Answer 1

electrical energy

Question 2

what do binary numbers represent?

Answer 2

ALL data in computers, including text, images, and sound.

Question 3

what does ASCII do

Answer 3

has codes for every character on a standard American English keyboard

Question 4

what does text file size depend on?

Answer 4

bits required to store each character - total number of characters in the file

Question 5

what is the text file size in bits

Answer 5

𝑇𝑒𝑥𝑡 𝐹𝑖𝑙𝑒 𝑆𝑖𝑧𝑒 𝑖𝑛 𝑏𝑖𝑡𝑠
= 𝑏𝑖𝑡𝑠 𝑝𝑒𝑟 𝐶h𝑎𝑟𝑎𝑐𝑡𝑒𝑟 × 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐶h𝑎𝑟𝑎𝑐𝑡𝑒𝑟𝑠

Question 6

what are the advantages of using Unicode over ASCII

Answer 6

• regularly updated to support more symbols
• can represent more characters than ASCII

Question 7

what are the disadvantages of using Unicode

Answer 7

requires more storage space, sometimes over 1 byte per character

Question 8

how are images in computers represented

Answer 8

images in computers are represented using dots

Question 9

what are the dots called

Answer 9

pixels

Question 10

what does ‘pixels’ stand for

Answer 10

PICture Elements

Question 11

how many colours do the pixels contain

Answer 11

contains only ONE colour

Question 12

how to form an image on a computer

Answer 12

• each colour is assigned a binary code
• each pixel is encoded with its colour code
• the codes for all the pixels in the image are arranged to form a bitmap

Question 13

how do you determine the size of an image

Answer 13

the size of an image is the total number of pixels in the image

Question 14

how do you calculate the size of the image

Answer 14

𝐼𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒 𝑖𝑛 𝑝𝑖𝑥𝑒𝑙𝑠 = 𝑊𝑖𝑑𝑡h × 𝐻𝑒𝑖𝑔h𝑡.

Question 15

what is colour depth

Answer 15

the number of colours in an image measured by the number of bits required to encode each pixel as a binary number

Question 16

what is a colour scale

Answer 16

the RGB scale – 24 bits indicating the respective intensity of red, green and blue from 0 to 255 for each colour

Question 17

what is a CLUT

Answer 17

colour look up table

Question 18

how many bits are needed to form a colour code

Answer 18

2 bits

Question 19

what does image file size depend on

Answer 19

𝐶𝑜𝑙𝑜𝑢𝑟 𝐷𝑒𝑝𝑡h × 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑃𝑖𝑥𝑒𝑙𝑠

Question 20

what does the quality of image depend on

Answer 20

• colour depth – with more colour depth,
  more colours can be displayed
• size – an image with more pixels is
  clearer due to a higher resolution

Question 21

what is sampling

Answer 21

the amplitude of a wave picked up at fixed times

Question 22

how many bits does ASCII use per character

Answer 22

7 bits

Question 23

how many unique values are there in ASCII

Answer 23

128

Question 24

why does ASCII have 128 unique characters

Answer 24

because 7 is the base, therefore; 2^7 = 128

Question 25

how does ASCII represent ‘48-57’ in code

Answer 25

numbers 0 to 9 in order (eg: 48 = 0, 49 = 1, etc)

Question 26

how does ASCII represent ‘65-90’ in code

Answer 26

capital letters A to Z in order (eg: 65 = A, 66 = B, etc)

Question 27

how does ASCII represent ‘97-122’ in code

Answer 27

small letters ‘a’ to ‘z’ in order (eg: 97 = a, 98 = b, etc)

Question 28

define ‘sample rate’

Answer 28

number of samples collected in one
second

Question 29

define ‘sample resolution’

Answer 29

number of bits used to store a single sample

Question 30

how does sampling work

Answer 30

• a microphone picks up sound wave and converts it to an electrical analogue signal
• the signal amplitude is sampled at regular intervals
• each sample is stored as a binary value

Question 31

why is sampling required

Answer 31

real world sound are analogue waves, which are continuous, continuous sound waves have an infinite number of amplitudes; computers do not have enough storage, so sampling is required to create digital waves (has limited number of values) which can be stored in a computer