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GCSE Computer science > 3.2: data representation > Flashcards

3.2: data representation Flashcards

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1
Q

how is text represented

A

represented by using a character set

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2
Q

ASCII

A

an example of a character set
can represent most letters, numbers and symbols by using only 1 byte

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3
Q

extended ASCII

A

first 128 values same as ASCII
ASCII but with more characters

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4
Q

unicode

A

limited to 256 characters
only useful in countries that have adopted the latin alphabet
includes technical symbols, punctuation and other characters

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5
Q

how many characters in unicode limited to

A

256

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6
Q

how are images represented

A

binary code is used to represent photographs and other images using bitmap

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7
Q

bitmap image

A

consists of a grid of squares called pixels
each pixel has its own position in the grid
each pixel is a single colour

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8
Q

what is used to represent the colour of a pixel

A

binary code

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9
Q

colour depth

A

the number of bits used to store each pixel’s colour
the greater the colour depth the more colours can be represented

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10
Q

3 colour depths

A

8-bit gradient
8-bit gradient, dithered
24-bit gradient

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11
Q

colours

A

combinations of: red, green and blue
any colour can be encoded as a set of 3 numbers

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12
Q

true colour

A

allocates 1 byte for red 1 byte for green and 1 byte for blue
this has a 24-bit colour depth( 3*8 = 24)

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13
Q

image resolution

A

clarity of an image
when you zoom into a bitmap image the pixels are streched so the quality is poor when you zoom in too much

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14
Q

how is image resolution expressed

A

the number of pixels that an image contains per inch
example: 300 ppi (pixels per inch)

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15
Q

image resolution (size of bitmapped graphic )

A

the size in pixels
width(in pixels) * height(in pixels)

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16
Q

image file size

A

width(in pixels) * height(in pixels) * colour depth
or image resolution(in pixels) * colour depth

example: 8 * 8 * 4 = 256 bits

17
Q

effects of higher resolution and colour depth

A

image is represented more accurately
larger file size

18
Q

metadata

A

additional information needed to able to read the binary data correctly and reproduce the image
addition information is image size and colour depth

19
Q

common file formats of bitmap graphics

A

bitmap
PNG (portable network graphic)
JPEG (joint photographic experts group)
GIF (graphics interchange format)

20
Q

sound

A

a vibration that travels through air

21
Q

sound waves

A

sound requires a source such as a human voice or musical instrument and a substance to travel through such as water or air

22
Q

anologue signal

A

particles vibrating and creating a sound wave

23
Q

how to convert sound to a series of binary numbers

A

digitisation converts analogue sound to a series of binary numbers

24
Q

amplitude

A

from center of wave to crest or trough
the height of a wave which relates to the amount of energy the wave carries measured in volts

25
Q

higher amplitude waves

A

carry more energy and are louder than waves with a lower amplitude

26
Q

time period

A

the time necessary to complete a cycle which is the wavelength

27
Q

formula for time period

A

time period = 1 / frequency

28
Q

frequency

A

the number of completed cycles per second

29
Q

high frequency

A

high pitch is produced

30
Q

low frequency

A

low pitch is produced

31
Q

cycle

A

when the sound wave passes between 2 consecutive points (crests or troughs)

32
Q

how to calculate frequency

A

calculate time taken to complete 1 cycle
unit is hertz(Hz)
1 hertz is 1 cycle per second

33
Q

sampling a sound

A

called sampling
the computer takes measurements of the anologue signal at a regular time intervals and converts it to a binary pattern

34
Q

calculating sample rate

A

how many times a sound is sampled per second
measured in hertz

35
Q

sample intervals

A

the time between 2 samples
the larger the sampling interval the lower the quality and the smaller the file

36
Q

sample resolution

A

number of bits used to represent each sample

37
Q

increasing sample rate

A

the higher the sampling rate the better the quality of the audio recording but it increases the size of the file

GCSE Computer science (14 decks)

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