1.2 - characters, images and compression

Question 1

What is a character set

Answer 1

All the characters a computer can use

Question 2

Two standard character sets in common use

Answer 2

ASCII, Unicode

Question 3

How many characters does ASCII have?

Answer 3

128, 7 bits

Question 4

How many characters does extended ASCII have?

Answer 4

256, 8 bits

Question 5

How many characters does Unicode have?

Answer 5

Over 65,000, 16 bits

Question 6

What is a pixel

Answer 6

A tiny square with a binary value

Question 7

Colour depth

Answer 7

Many images need colour, more bits are required for each pixel, more bits = more colours. The more colours, the more bits per pixel so the more the colour depth so the larger the image file

Question 8

Image size

Answer 8

Number of pixels than an image contains, expressed as height and width

Question 9

Resolution

Answer 9

How many pixels there are in a certain distance. Higher resolution looks better

Question 10

Meta data

Answer 10

Data about the file itself e.g. file type, data created, author, height and width of image, resolution, colour depth

Question 11

Two types of compression

Answer 11

Lossy and lossless

Question 12

Lossy compression

Answer 12

Some data is removed thereby reducing the overall amount of data and file size

Question 13

Image in lossy compression

Answer 13

Reduce colour depth, some shades will be discarded

Question 14

Audio file in lossy compression

Answer 14

Reduce bit depth

Question 15

Files compatible with lossy compression

Answer 15

JPEG, MPEG, MP3

Question 16

Lossless compression

Answer 16

Files are reduced in size without removing data, can be done by looking for repeats in data and storing it as one item of data instead of many

Question 17

Files compatible with lossless data

Answer 17

PDF, GIF

Question 18

How is sound converted to binary

Answer 18

Capture a sound wave at regular intervals, using an analogue-to-digital converter, this is known as a sample. The sound recorded at each sample is converted to its nearest numeric equivalent

Question 19

Sample rate

Answer 19

Number of samples recorded in a given time period, higher the sample rate = closer to original sound, measured in hertz

Question 20

Bit depth

Answer 20

Number of bits used to record each sample

Question 21

Bit rate

Answer 21

Measure of how much data is processed for each second of sound