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AS Computer Science > Chapter 1 - Information Representation + Multimedia > Flashcards

Chapter 1 - Information Representation + Multimedia Flashcards

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1
Q

Binary

A

Base 2 number system based on the values of 1 and 2 only

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2
Q

Bit

A

Abbreviation for binary digit

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3
Q

One’s compliment

A

Each binary digit in a number is reversed to allow both negative and positive numbers to be represented

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4
Q

Two’s compliment

A

Each binary digit is reversed and 1 is added to represent positive and negative numbers

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5
Q

Sign and magnitude

A

Binary number system where the left-most bit represents the sign (0=+, 1=-) and the remaining bits the binary value

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6
Q

Hexadecimal

A

Base 16 number system (0-9, A-F)

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7
Q

Memory dump

A

Contents of a computer memory output to a screen/computer

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8
Q

BCD

A

Binary coded Decimal
Number system that uses 4 bits to represent each denarydigit

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9
Q

ASCII code

A

Coding system for all the characters on a keyboard and control codes

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10
Q

Character set

A

List of characters defined by computer hardware and software so that the computer can understand human characters

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11
Q

Unicode

A

Coding system which represents all the languages of the world (first 128 are the same as ASCII)

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12
Q

Byte

A

Smallest unit of memory in a computer system

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13
Q

Uses of BCD

A

Representation of digits on a clock/calculator display

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14
Q

Difference between upper and lowercase in Unicode

A

Add 32 to uppercase to get lowercase (causes the 6th bit from the right to change to a 1)

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15
Q

Difference between ASCII and Unicode (2)

A

1 vs 4 byte character representation
Only English vs all languages of the world

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16
Q

Goals for Unicode (5)

A

Universal standard for all languages +writing systems
Reserve part of code for private use
Create unambiguous coding (each 16/32 bit value always represents the same thing)
Uniform encoding where each character is 16 or 32 bits
More efficient coding system than ASCII

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17
Q

Bit-map image

A

System that uses pixels to make up an image

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18
Q

Pixel

A

Smallest picture element that makes up an image

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19
Q

Colour depth

A

Number of bits used to represent the colours in a pixel eg 8 bit colour depth is 2^8=256 colours

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20
Q

But depth

A

Number of bits used to represent the smallest unit in a sound/image file (larger the depth, the better the quality)

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21
Q

Image resolution

A

Number of pixels that make up an image

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22
Q

Screen resolution

A

No. Of horizontal and vertical pixels that make up a screen display.

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23
Q

What happens if the screen resolution is smaller than the image resolution

A

The whole image cannot be shown on the screen or the original image will become lower quality

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24
Q

Resolution

A

Number of pixels per column and per row on a monitor/TV screen

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25
Q

Pixel density

A

Number of pixels per square centimetre

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26
Q

Vector graphics

A

Images that use 2D points to describe lines + curves + their properties that are grouped to form geometric shapes

27
Q

Sampling resolution

A

Number of bits used to represent sound amplitude (bit depth)

28
Q

Sampling rate

A

Number of sound samples taken per second (horizontal/line of propagation)
Rate at which the DAC can translate the digital output into analogue voltages

29
Q

Frame rate

A

Number of video frames that make up a video per second

30
Q

What to consider when storing images as pixels (3)

A

At least 8 bits per pixel are needed
True colour requires 3 bytes per pixel
Number of bits used to represent a pixel is the colour depth

31
Q

Difference between bit depth and colour depth

A

No. Of bits used to represent a single pixel determines the colour depth. The higher the bit depth the more possible colours can be represented

32
Q

How to find pixel density

A

Add the squares of the resolution size
Find the square root
Divide by screen size

33
Q

Drawback of high resolution images

A

Large file size

34
Q

What to do when saving a bit-map image

A

Include a file header which has things like file type (eg. .jpeg), file size, image resolution, bit depth and any type of data compression employed

35
Q

How can vector graphics be designed (2)

A

Computer aided design (CAD)
Application which uses a canvas on a screen

36
Q

Contents of vector graphic drawing list (4)

A

Command used for each object that makes up the graphic image
Attributes that define properties that make up each object (thickness, line colour etc.)
Relative position of each object
Relative positions of objects to each other (so that up-scaling won’t reduce the quality)

37
Q

Vector graphic images vs Bit-map images (5)

A

Made up of geometric shapes requiring definitions/attributes - tiny pixels of different colours
Need to change each of the geometric shapes to edit - can edit each of the pixels
Made up of simple geometric shapes so don’t require large file size -very large file size (pixels)
Limited no. of geometric shapes so not very realistic - usually very realistic
File formats usually .svg, .cgm, .odg

38
Q

Vector graphic images vs Bit-map images (5)

A

Made up of geometric shapes requiring definitions/attributes - tiny pixels of different colours
Need to change each of the geometric shapes to edit - can edit each of the pixels
Made up of simple geometric shapes so don’t require large file size -very large file size (pixels)
Limited no. of geometric shapes so not very realistic - usually very realistic
File formats usually .svg, .cgm, .odg

39
Q

When should a vector graphic be used (2)

A

If the image needs to be resized
If the image needs to be drawn to scale

40
Q

When should bit-map images be used (2)

A

If the image needs to look real
If there are file restrictions (consider the image resolution of image to ensure size not too big)

41
Q

Sound

A

Analogue Transmitted by causing oscillations of particles within a medium. The human eye picks up these oscillations (changes in air pressure) and interprets them as sound. Each wave has a frequency and wavelength and amplitude which specifies the loudness of the sound

42
Q

How sound is stored

A

It is digitised using an Analogue to Digital Converter. It is filtered to remove frequencies out of the human hearing range, then the sound waves are sampled at a given time rate and approximate amplitude values are stored

43
Q

How is sampling used to record a sound clip (3)

A

Amplitude of the sound wave is determined at set time intervals
An approximate representation of the sound wave is given
Wave is encoded as a series of binary digits

44
Q

Pros of a high sampling rate/resolution (3)

A

Larger dynamic range
Better sound quality
Less sound distortion

45
Q

Cons of higher sampling rate/resolution (3)

A

Produces large file size
Takes longer to transmit/download sound files
Requires greater processing power

46
Q

Features of recorded sound editing software (8)

A

Edit start/stop times + duration of a sample
Extract + save/delete part of sample
Alter frequency + amplitude of the sample
Fade in + out
Mix/merge multiple sound tracks and sources
Combine various sound sources together and alter their properties
Remove noise to enhance one sound wave in a multiple of waves
Convert between different audio formats

47
Q

Lossless file compression

A

File compression method where the original file can be restored following decompression

48
Q

Lossy file compression

A

File compression method where parts of original file cannot be recovered during decompression (some detail is lost)

49
Q

JPEG

A

Joint Photographic Expert Group
Form of lossy file compression based on the inability of the eye to spot certain colour changes and hues

50
Q

MP3/MP4 files

A

File compression method used for music and multimedia files

51
Q

Perceptual music shaping

A

Method where eg. sounds outside normal range of hearing of humans are eliminated during compression

52
Q

Audio compression

A

Method to reduce size of a sound file using perceptual music shaping

53
Q

Bit rate

A

No. Of bits per second that can be transmitted over a network. Its a measure of the data transfer rate over a digital telecoms network

54
Q

RLE

A

Run length encoding
Lossless file compression technique used to reduce text and photo files in particular

55
Q

Most common forms of file compression (2)

A

Lossless file compression
Lossy file compression (JPEG/MP3)

56
Q

File compression applications (3)

A

MPEG 3 and MPEG 4
Photographic (bit-map) images
RLE

57
Q

MPEG-3

A

Uses audio compression (perceptual music shaping) to convert music and other sounds into a MP3 file format (lossy compression), reducing the size by about 90%.

58
Q

What perceptual music shaping removes (2)

A

Sounds outside human hearing range
If 2 sounds are played simultaneously, the softer one is eliminated

59
Q

MPEG-4

A

Allows storage of multimedia files rather than just sound.

60
Q

Photographic (bitmap) images

A

JPEG, reduces the image by a factor between 5 and 15
Scalable Vector graphics (svg) are defined in XML text files, allowing them to be compressed

61
Q

RLE

A

Run Length Encoding
Form of lossless file compression that reduces the size of a string of adjacent, identical data by encoding it into 2 values.
1st: number of identical items
2nd: code of the data item

62
Q

General methods to compress movie files (3)

A

Reduce the sampling rate
Reduce sampling resolution
Reduce frame rate

63
Q

General methods to compress image files (3)

A

Crop the image
Decrease the colour/bit depth
Reduce the image resolution

AS Computer Science (4 decks)

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