3-4: Images and Sound

Question 1

what does pixel stand for

Answer 1

picture element
smallest addressable part of an image

Question 2

what is colour depth

Answer 2

the number of bits stored for each pixel which represents the colour

Question 3

explain how bitmap images work

Answer 3

they are images stored in the computer memory as a grid of pixels - each pixel is stored as a specific colour

Question 4

explain how vector images work

Answer 4

these images are stored as shape/objects using specific properties of the shape
eg, rectangle(2,2,8,8,light blue) - this means draw a rectangle with left corner 2,2 and top right corner 8,8 and fill w light blue

Question 5

what is the resolution of an image

Answer 5

width of image in pixels x height of image in pixels

Question 6

state 4 advantages of vector images

Answer 6

-does not deteriorate when enlarged
-usually faster to load
-usually uses less memory
-easier to edit

Question 7

how do u convert an analogue sound to digital form

Answer 7

analogue to digital converter
ADC

Question 8

how do u convert a digital sound to analogue form

Answer 8

digital to analogue converter
DAC

Question 9

describe the process of a computer recording sound and then playing it through a loudspeaker

Answer 9

-microphone picks up the sound waves
-the sound wave is amplified
-an ADC converts the analogue signal to digital
-to play back the recorded sound a digital to anologue converter (DAC) is used
-the signal is then played through a loudspeaker

Question 10

what are samples

Answer 10

measuring the value of the analogue signal at regular intervals

Question 11

what is CD’s sampling rate

Answer 11

44,000 every second
44 kHz

16-bit amplitude

Question 12

what is Nyquists theroem

Answer 12

the sampling rate should be at least double the highest frequency of the sound wave being sampled

Question 13

what is MIDI

Answer 13

system that allows electronic musical instruments and computers to send instructions to eachother

Question 14

give 3 advantages of MIDI

Answer 14

-can easily synthesise musical notation
-easy to manipulate data
-no data is lost

Question 15

why is streaming audio sometimes preferable to downloading the sound file

Answer 15

less memory required
unlimited access

Question 16

in simple terms, how does streaming work

Answer 16

the video loads a little bit at a time instead of the entire file loading at once and the information is not saved locally

Question 17

explain the difference between an analogue signal and a digital

Answer 17

analogue is continuous and digital is discrete

Question 18

what is the equation to calculate filesize of a sound

Answer 18

filesize = sampling frequency * bit depth * length

Question 19

desribe the principles of operation of an analogue to digital converter

Answer 19

• the analogue signal is sampled at regular time intervals
• the amplitude of the signal is measured
• the measurement is then coded in binary

Question 20

how do you calculate storage requirements for bitmapped images

Answer 20

width x height x colour depth

Question 21

describe the difference between lossless and lossey compression

Answer 21

• lossey reduces a file size by eliminating certain information
• lossless keeps every bit of data originally in the file

Question 22

how does MIDI represent music

Answer 22

• sequence of MIDI event messages
• one exampled of data that might be contained in a message is the volume

Question 23

what is metadata and give an example

Answer 23

• data that provides information
• location, author, time it was taken

Question 24

describe the principles behind the technique of run length encoding

Answer 24

• identifies sequences of identical data
• represents these as one data value with a count of how many such values are in the sequence

Question 25

how do you convert bits into megabytes (MB)

Answer 25

• divide by 8
• divide by 1 000 000