Topic 5.6 - Representing Images, Sound and other Data (incomplete)

Question 1

How do bit patterns represent images

Answer 1

image height * image width * colour depth (in bits)

Question 2

Difference between Analogue and Digital Data

Answer 2

Analogue data is continuous meaning there are no limits
Digital data is discrete meaning it can only take particular values

Analogue data can change as quickly as required
Digital data can only change at specific intervals

Question 3

Difference between Analogue and Digital Signals

Answer 3

Analogue signals are smooth curves
Digital signals have sharp edges

Question 4

How does an Analogue to Digital Converter (ADC) work

Answer 4

Works by taking a reading of an analogue signal at regular intervals and recording the value; called sampling

Samples are taken at a specific frequency (in Hertz (Hz)) which determines number of samples taken per second.
Needs to be a high frequency for better accuracy in reproducing the signal

Once signal has been recorded, it is stored digitally as a bit pattern

Question 5

How does a Digital to Analogue Converter (DAC) work

Answer 5

Device reads the bit pattern of the audio signal and outputs an analogue electrical current

Question 6

What is the most common use for a Digital to Analogue Converter (DAC)

Answer 6

To convert a digital audio signal into an analogue signal

Question 7

What are ADC’s used for

Answer 7

Many sensors like microphones and thermometers which output analogue signals.

Question 8

Explain how bitmaps are represented

Answer 8

An image is broken down into pixels
Each pixel is given a binary value which represents a colour

Question 9

What is resolution

Answer 9

The number of pixels per square inch.

Question 10

What is meant by the term Pixel

Answer 10

Picture element
A small square that makes up an image
More pixels = Higher resolution

Question 11

What is colour depth

Answer 11

The number of bits stored for each pixel
if the colour depth is 5 then there will be 2^5 colours available.

Question 12

What is the size of an image in pixels

Answer 12

Width of the image in pixels
*
Height of the image in pixels

Question 13

What is the calculation for the storage required of a bitmapped image

Answer 13

Width * Height * Colour Depth(in bits)

Question 14

What are some common examples of metadata

Answer 14

Location, time, date

Question 15

How does vector graphics represent images

Answer 15

By using objects and shapes (rectangles, circles, lines)
The properties of each object & shape are stored as a list

Question 16

What are the typical properties of objects used in vector graphics

Answer 16

Height
Width
Fill Colour
Start Position

Question 17

Advantages of Bitmap Graphics over Vector Graphics

Answer 17

Used for storing photographs and highly detailed images
Vectors can only store simple images

Question 18

Advantages of Vector Graphics over Bitmap Graphics

Answer 18

Images can be scaled with no loss of quality
Bitmap cant

Vectors use less storage space since they only have to store information about each shape rather than each pixel.

Question 19

Explain Digital Representation of Sound

Answer 19

Computers represent sound as a sequence of samples which each hold a specific digital value

The number of bits allocated to each sample is called the sample resolution

A greater sample resolution results in greater audio quality but greater file size

Question 20

What is the calculation for the size of a sound sample

Answer 20

Duration of sample (in secs)
*
The sampling rate (in Hz)
*
The sample resolution

Question 21

What is The Nyquist Theorem

Answer 21

The sampling rate of a digital audio file must be at least twice the frequency of the sound.
Otherwise the sound may not be accurately represented.

Question 22

What is the purpose of Musical Instrument Digital Interface (MIDI)

Answer 22

Allows electronic musical instruments to be able to communicate with each other

Question 23

How does MIDI work

Answer 23

Instead of storing samples of sound, MIDI stores sound as a series of event messages.

Each event message represents an instruction in a piece of music. E.G. :
Duration of a note
Instrument being used
Volume of note
Which note is being played

Question 24

What are the advantages of using MIDI to represent music

Answer 24

Easy to manipulate music without loss of quality
Smaller file size
Lossless files

Question 25

What are the disadvantages of using MIDI to represent music

Answer 25

Sometimes results in a less realistic sound than a sample recording does
Cannot store speech

Question 26

5.6.9 and 5.6.10