3.3 - Image & Sound Representation (6 + 7)

Question 1

what is a pixel?

Answer 1

tiny single point in a graphical image which makes up a picture

Question 2

how is each pixel displayed?

Answer 2

using a binary representation

Question 3

what is a bitmap?

Answer 3

the binary stored data representing an image

Question 4

what is the term ‘pixel’ short for?

Answer 4

picture element

Question 5

what is a VDU?

Answer 5

a virtual display unit

Question 6

how do VDUs display pictures?

Answer 6

dividing the display screen into thousands of pixels (arranged into rows and columns)

Question 7

how do you display the size of a bitmap (in pixels)?

Answer 7

width of image (in pixels) x height of image (in pixels)

Question 8

define colour depth

Answer 8

the number of bits used to represent each pixel

Question 9

what is the image resolution?

Answer 9

in terms of pixels

width x height

Question 10

how does a bitmap represent an image using pixels and colour depth?

Answer 10

• bitmap images are organised as a grid of coloured squares (pixels)
• each colour of image is stored as a binary number
• bits of info are stored in the bitmap

Question 11

how does the number of pixels and colour depth affect the file size of a bitmap image?

Answer 11

the higher number of pixels and higher colour depth, the larger the file size

Question 12

how do you calculate the size (in bits) of an image?

Answer 12

image width x image height x colour depth

Question 13

how do you calculate the size of an image in bytes?

Answer 13

(image width x image height x colour depth depth) / 8

• same as bits (just divide by 8)

Question 14

what is metadata?

Answer 14

extra details about an image (location, colour depth, file name, camera details)

Question 15

define image resolution

Answer 15

a measure of pixel density and the quality of the image (by the distance between two adjacent pictures)

Question 16

sound is …….. and must be converted to a ……….. ……….. for …… and ……….. in a computer

Answer 16

analogue, digital form, storage, processing

Question 17

what process is carried out for digital versions of sound to be made?

and explain briefly what it is

Answer 17

sampling, a sound measurement taken at a given point in a sound file

Question 18

what is a sample?

Answer 18

a measure of amplitude at a point in time

Question 19

describe the processes in which a sound wave is converted to a sound file

Answer 19

1. measure the amplitude of sound wave at specific intervals (sampling)
2. convert values to binary
3. store into the sound file

Question 20

what is the sampling rate?

Answer 20

the number of samples taken in a second (measured in hertz)

Question 21

what is the sample resolution?

Answer 21

number of bits used to store each sample

Question 22

how does a sampling rate for a sound file affect the size?

Answer 22

makes the file larger (as it has more samples to store)

Question 23

formula to calculate file size based on sampling rate and resolution? (sound)

Answer 23

sample rate x sample resolution x number of seconds x channels

Question 24

describe how a physical image can be represented in a bitmap

Answer 24

• bitmap images organised as a grid of coloured squares (pixels)
• each colour stored as a binary number
• bits of information are stored in the bitmap

Question 25

what is sampling?

Answer 25

when analogue sound is converted into a set of binary numbers

Question 26

what is an ADC?

Answer 26

a device that converts real-world analogue signals into digital signals

Question 27

define a bit rate

Answer 27

the amount of information used to describe one second of sound (ie. the number of bits per second)

Question 28

formula to calculate bit rate?

Answer 28

sample rate x bit depth x number of channels

Question 29

what are the advantages of digital signals?

Answer 29

they are easy to copy, transmit and store

Question 30

what does a DAC do?

Answer 30

converts a binary stored version of a recording to voltage that speakers can reproduce

Question 31

what is the common sampling rate for sound files?

Answer 31

44.1 kH

Question 32

how would a greater number of samples per second affect a sound file?

Answer 32

higher quality of sound, larger file size (greater data stored)