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Computer Science > Representing Images, Sound and Other Data > Flashcards

Representing Images, Sound and Other Data Flashcards

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1
Q

Describe Analogue Data

A

Continuous

No Limits to the values that the data can take

Can be changed as frequently as required

Smooth curves which feature sharp peaks

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2
Q

Describe Digital Data

A

Discrete

Can only take particular values

Can only take one of a specific range of values

Can only change values at specified intervals

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3
Q

What does a DAC stand for

A

Digital to Analogue converter

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4
Q

How does a DAC work

A

It reads a bit pattern representing an analogue signal and outputs an alternating, analogue, electrical current

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5
Q

What outputs an analogue signal

A

Temperature sensors and microphones

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6
Q

What does ADC stand for

A

Analogue to Digital Convertor

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7
Q

How does an ADC work

A

Takes a reading of an analogue signal at regular intervals

Records the value through sampling

Samples are taken at a specific frequency

Once the signal is recorded - it can be stored digitally as a bit pattern representing its amplitude

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8
Q

What are bitmap graphics and how do they work ————

A

A way a computer can represent an image

An image is broken down into pixels - each pixel is assigned a binary value

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9
Q

How is the resolution of an image represented ———–

A

Number of dots per square inch

OR

Number of pixels in an image

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10
Q

How big is a dot ——

A

A pixel

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11
Q

What determines the colour of a pixel ————–

A

The binary value assigned to it

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12
Q

What is the colour depth —————-

A

Number of bits assigned to a pixel in an image

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13
Q

How do you calculate the storage required to represent a bitmap image and what does this method tell you ————

A

Resolution x Colour Depth

Minimum amount of bits required due to the files containing metadata

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14
Q

What do vector graphics represent and how and what are the properties stored in ————–

A

Images using geometric objects and shapes

A list

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15
Q

Why can vector graphics be scaled without losing quality ———–

A

They use shapes instead of pixels

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16
Q

Uses for Vector Graphics ————

A

Simple images such as company logos

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17
Q

Uses for bitmapped graphics ————

A

Storing photos

18
Q

Why do vector graphics frequently use less storage space than bitmapped graphics ———————

A

Information is stored for each shape rather than for every single pixel

19
Q

How do computers represent sound

A

As a sequence of samples

20
Q

What does a sample take

A

Discrete digital values

21
Q

What is the sampling rate

A

Number of Samples per second

Measured in Hz

22
Q

What is the sample resolution

A

Number of bits allocated to each sample

23
Q

What comes with higher sample resolutions

A

Greater audio quality and increased file size

24
Q

How can the size of a sound sample be calculated

A

Sample rate x sample resolution x length of sample

25
Q

What is the Nyquist Theorem

A

Sampling rate of a digital audio file must be at least twice the frequency of the sound

26
Q

What does MIDI stand for

A

Musical Instrument Digital Interface

27
Q

When are MIDIs used

A

With electronic musical instruments which can be connected to computers

28
Q

How does a MIDI work

A

Stores sound as a series of event messages - each of which represents an event in a piece of music

29
Q

Advantages of MIDI over samples

A

Easy manipulation of music without loss of quality (lossless)

Notes can be transposed and the duration of notes can be altered

Smaller in Size

30
Q

What are the two types of compression

A

Lossy and Lossless

31
Q

What is Lossy Compression

A

Compression where some information is lost

Quality of File is Reduced

The extent to which file size can be reduced is not limited

32
Q

What is Lossless Compression

A

Compression where no information is lost

There is no loss of quality

There is a limit to how much file can be compressed

33
Q

Define Encryption

A

The process of scrambling data so that it cannot be understood if intercepted in order to keep it secure during transmission

34
Q

What is Plaintext

A

Unencrypted information

35
Q

What is Ciphertext

A

Encrypted information

36
Q

What is a cipher

A

A type of encryption method

37
Q

What is a Vernam Cipher

A

A one time pad cipher which requires the key to be random

38
Q

How does a Vernam Cipher work

A

Align the characters of the plaintext and the key

Convert each character to binary using an information coding system

Apply a logical XOR operation to the two bit patterns

Converting the result back to a character

39
Q

How many bit patterns can series of bits represent

A

2^n

40
Q

What does the size of an image dtermine

A

Number of rows and columns of pixels that create the image

41
Q

Relationship between size and resolution

A

Inversely proportional

42
Q

Formula for resolution

A

Width in pixels x height in pixels

Computer Science (16 decks)

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