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

Chapter 1 - Information Representation + Multimedia Flashcards

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

Bit 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
Pixel density
Number of pixels per square centimetre
26
Vector graphics
Images that use 2D points to describe lines + curves + their properties that are grouped to form geometric shapes
27
Sampling resolution
Number of bits used to represent sound amplitude (bit depth)
28
Sampling rate
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
Frame rate
Number of video frames that make up a video per second
30
What to consider when storing images as pixels (3)
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
Difference between bit depth and colour depth
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
How to find pixel density
Add the squares of the resolution size Find the square root Divide by screen size
33
Drawback of high resolution images
Large file size
34
What to do when saving a bit-map image
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
How can vector graphics be designed (2)
Computer aided design (CAD) Application which uses a canvas on a screen
36
Contents of vector graphic drawing list (4)
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
Vector graphic images vs Bit-map images (5)
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
Vector graphic images vs Bit-map images (5)
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
When should a vector graphic be used (2)
If the image needs to be resized If the image needs to be drawn to scale
40
When should bit-map images be used (2)
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
Sound
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
How sound is stored
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
How is sampling used to record a sound clip (3)
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
Pros of a high sampling rate/resolution (3)
Larger dynamic range Better sound quality Less sound distortion
45
Cons of higher sampling rate/resolution (3)
Produces large file size Takes longer to transmit/download sound files Requires greater processing power
46
Features of recorded sound editing software (8)
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
Lossless file compression
File compression method where the original file can be restored following decompression
48
Lossy file compression
File compression method where parts of original file cannot be recovered during decompression (some detail is lost)
49
JPEG
Joint Photographic Expert Group Form of lossy file compression based on the inability of the eye to spot certain colour changes and hues
50
MP3/MP4 files
File compression method used for music and multimedia files
51
Perceptual music shaping
Method where eg. sounds outside normal range of hearing of humans are eliminated during compression
52
Audio compression
Method to reduce size of a sound file using perceptual music shaping
53
Bit rate
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
RLE
Run length encoding Lossless file compression technique used to reduce text and photo files in particular
55
Most common forms of file compression (2)
Lossless file compression Lossy file compression (JPEG/MP3)
56
File compression applications (3)
MPEG 3 and MPEG 4 Photographic (bit-map) images RLE
57
MPEG-3
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
What perceptual music shaping removes (2)
Sounds outside human hearing range If 2 sounds are played simultaneously, the softer one is eliminated
59
MPEG-4
Allows storage of multimedia files rather than just sound.
60
Photographic (bitmap) images
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
RLE
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
General methods to compress movie files (3)
Reduce the sampling rate Reduce sampling resolution Reduce frame rate
63
General methods to compress image files (3)
Crop the image Decrease the colour/bit depth Reduce the image resolution

AS Computer Science (10 decks)

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