3.2 Data Representation

Question 1

What are the possible textual representations?

Answer 1

1. ASCII
2. Unicode

Question 2

What is ASCII?

Answer 2

ASCII contains characters encoded with character sets → codes assigned to a character.

Originally only 7 bits long, but extended to 8 to contain 256 characters.

Question 3

What is Unicode?

Answer 3

Unicode was created due to ASCII’s inability to represent all possible characters.

ASCII is a subset of Unicode, Unicode uses 16 bits, having codes for 120 000 characters.

Question 4

What are encoding tables?

Answer 4

Character codes are sequential, so it is in ascending order. To find the code for another character, simply add to where a previous one is.

Question 5

What is a pixel?

Answer 5

The smallest distinguishable feature.

Question 6

How are images represented in binary?

Answer 6

Bitmaps, images are stored as an array of individual pixels.

Question 7

How do you calculate an image’s size?

Answer 7

Pixel Width x Height

Question 8

What is the resolution of an image?

Answer 8

It is the detail that an image holds, aka pixels per inch.

Question 9

How is an image converted from analogue to digital?

Answer 9

1. A grid is placed over the image
2. An average colour is found for each pixel and assigned a binary value
3. Each pixel is represented by multiple bits, one combination a shade
4. The number of bits in a pixel is called the colour/bit depth.

Question 10

What affects an image’s size?

Answer 10

Increasing Resolution; Increasing Colour Depth

Size = Pixel Size x Colour Depth (in bits)

Question 11

What is Metadata?

Answer 11

It is data about data, for example it allows the image to be displayed properly as well as other unneeded data:

1. File name; format; colour depth; resolution; camera details

Question 12

What is the difference between analogue and digital data?

Answer 12

Analogue signals are continuous, represented by waves.

Digital data is discrete, falling between defined ranges and taking only certain values.

Computers require digital data, as it cannot read analogue signals.

Question 13

What is a sampling frequency?

Answer 13

It is the number of samples obtained over second, measured in hertz. The greater the sampling frequency, the better quality but the larger file.

Question 14

How is sound digitized?

Answer 14

1. Several samples should be taken at regular intervals, with a binary value given to each reading

Question 15

What is a sample size?

Answer 15

It is the bit depth

Question 16

What is the bit rate?

Answer 16

It is the number of bits used per second

Bit rate = Sampling Frequency x Sample Size

Question 17

How is a sound file size calculated?

Answer 17

It is the Sampling Frequency x Sample Size x Time

Question 18

What is Compression and the Two Types of it?

Answer 18

Compression is the reduction of file size without losing important information.

1. Lossy
2. Lossless

Question 19

What is Lossy Compression?

Answer 19

Lossy compression is a means of compression in which data is removed and lost forever. Some quality can be lost.

E.g JPEG, MP3, MP4

Question 20

What is Lossless Compression?

Answer 20

No data is removed here - it is maintained, but it is rearranged, for example using Run Length Encoding.

1. Repeated data is replaced with frequency
2. The more data the more the file can be compressed
3. Can be restored fully

Question 21

What is Encryption?

Answer 21

It is the process of making data secret so only authorised viewers can decrypt and read the data.

It doesn’t prevent interception, it simply stops it from being understood.

Question 22

What is the simplest process of Encryption?

Answer 22

Plaintext → Ciphertext → Message Sent → Message Received → Message Decrypted

Question 23

Why is Encription Required?

Answer 23

1. It is needed to protect data, especially important ones
   
   1. Bank information, government details, identity information