2. Data Representation - Multimedia Flashcards

1
Q

How do we perceive sound?

A

Series of air compression vibrates membrane in our ear –> sends signal to our brain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does a stereo work?

A

Sends electrical signal to a speaker to produce sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the signal in sound representations?

A

Analogous representation of sound wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How do we digitize sound signal?

A

Sample sound periodically –> measure voltage –> record the numeric value

Sample rate of 40 000 times per second needed for reasonable sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Audio Formats

A

WAV
MP3

Based on storage of voltage values sampled from analog signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How do we perceive colour?

A

–> detect frequencies of light that reach the retinas of our eyes

–> retinas have 3 types of colour photoreceptors –> RGB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

RGB

A

Values indicate the relative contribution of each of the primary colours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Colour depth

A

Amount of data used to represent per pixel

High colour –> 16 bit col depth:
-5 bits per RGB
-extra bit can represent transparency

True colour: 24 bit representation
- 8 bits per RGB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Representing graphics

A

Photo –> analogue rep of an image

Digitization: pixels used to rep an image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Raster Graphics

A

Stores data on pixel-by-pixel basis

BITMAP: contains pixel colour values of the image from left to right and top to bottom

GIF: limits number of colours per image to 256

JPEG: averages out colour hues over short distances

PNG: like GIF but achieves greater compression with wider range of colour depth values

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Vector Graphics

A

Describes images in terms of lines and geometric shapes

Images created directly from geom. shapes that are defined on cartesian plane (points, lines, curve…)

Not every pixel is described –> smaller file size

Two formats:
1) Adobe & Flash
2) Scalable Vector Graphics (SVG)

Advantage: can be resized mathematically

NOT GOOD for representing real world images

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Types of redundancy in digital image

A

1) Coding redundancy

2) Inter-pixel Spacial redundancy

3) Inter-pixel Temporal redundancy

4) Psychovisual Redundancy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Coding Redundancy

A

Grey levels of an image are coded using more code symbols than necessary

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Inter-pixel Spacial Redundancy

A

Due to correlation between the neighboring pixels in an image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Inter-pixel Temporal Redundancy

A

Statistical correlation between pixels from successive frames in a video sequence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Psychovisual Redundancy

A

We do not perceive images by analysing every pixel in an image

17
Q

JPEG

A

Standard for saving images

18
Q

Factors determining video file size in relation to quality

A

1) Time : longer = bigger files

2) Number of pixels (resolution) –> larger = bigger files

3) Frame rate: higher = bigger files

4) Amount of motion in the video: more = bigger files

19
Q

Spatial Compression

A

Removes redundant information within a frame

20
Q

Temporal Compression

A

Aims to reduce differences between consecutive frames

21
Q

Frame types

A

1) Intra-coded frames (I-frames)

2) Predicted frames (P-frames)

3) Bi-directional frames (B-frames)

22
Q

Reference Frame

A

Frame used as a reference for predicting other frames

23
Q

I-Frames

A

Frame that is encoded with no reference to other frames

Have the least amount of compression

24
Q

Predicted Frames

A

Encoding based on preceding I or P frame –> helps save bits

–> risk is error propagation

25
Q

B-frames

A

Inter-coded, Interpolation frames

saves even more bits than P

Used to combat fast moving objects

26
Q

Macroblocks

A

Pictures (frames) usually segmented into macroblocks

Individual prediction types can be selected on a macroblock basis rather than being the same for the entire picture