5.6 representing images, sound etc..

Question 1

Analogue data is

Answer 1

continous

Question 2

digital data is

Answer 2

discrete

Question 3

analogue signals take

Answer 3

any value and can change frequently

Question 4

digital signals must always take

Answer 4

one of a specified range of values, can only change value at specified intervals

Question 5

how do you convert from digital to analogue

Answer 5

use digital to analogue converter

Question 6

most common use of digital to analogue converter

Answer 6

converting digital audio signals to analogue

Question 7

what is sampling in digital to analogue conversion

Answer 7

taking reading of analogue signal at regular intervals and records the value

Question 8

sampling taken at specific freq in

Answer 8

hertz

Question 9

bitmapped graphics, images are broken into

Answer 9

pixels

Question 10

each pixel assigned

Answer 10

binary value

Question 11

value assigned to pixel determines

Answer 11

colour

Question 12

resolution

Answer 12

no. of pixels in image

Question 13

no. of bits assigned to pixel is

Answer 13

colour depth

Question 14

storage required =

Answer 14

no of. pixels x bit depth

Question 15

metadata include

Answer 15

width, height, date

Question 16

vector graphics are

Answer 16

geometric objects and shapes used to create images

Question 17

vector vs bitmap

Answer 17

vector:
can be scaled without losing quality
less storage space

bitmap oppo

Question 18

Nyquist theorem

Answer 18

sampling rate must be at least twice freq of signal

Question 19

midi stands for

Answer 19

musical instrument digital interface

Question 20

benefits of midi

Answer 20

easy manipulation of music (without losing quality)
notes can be transposed
midi files often smaller

Question 21

dis of midi

Answer 21

can’t store speech

less realistic sound

Question 22

lossy compression

Answer 22

files reduced in size
some info lost
quality reduced
no limit to compression applied

Question 23

lossless comp

Answer 23

no info lost
quality same
limit to amount of comp

Question 24

RLE

Answer 24

run-length coding

removes repeated info

Question 25

Dictionary based methods

Answer 25

● A dictionary containing repeated data is appended to the file
● Results is a significant reduction in size
● The dictionary used to compress the data must be present in the file
● This will increase the size of the compressed file

Question 26

unencrypted info is called

Answer 26

plaintext

Question 27

encrypted info called

Answer 27

cipher

Question 28

what must you know to encrypt plaintext

Answer 28

key

Question 29

caesar ciphers

Answer 29

replace characters

Question 30

two types of casar cipher

Answer 30

shift and sub

both easy to crack

Question 31

shift cipher

Answer 31

all letters shifted by same amount

Question 32

sub cipher

Answer 32

letters randomly placed

Question 33

vernam ciphers

Answer 33

each key only used once

key must be random

Question 34

computational security

Answer 34

all ciphers apart from vernam are crackable, with time and computer power