1.2.4 & 1.2.5 - Data Storage and Compression

Question 1

A character set is…

Answer 1

All the characters a computer can represent with a unique binary code representing each character

Question 2

The size of an ASCII character is…

Answer 2

8 bits

Question 3

The size of a Unicode character is…

Answer 3

2-4 bytes

Question 4

Unicode character sets represent…

Answer 4

All the different characters/languages of the world

Question 5

ASCII character sets represent…

Answer 5

A few European languages’ characters

Question 6

An image is made up of…

Answer 6

Pixels

Question 7

Image metadata includes…

Answer 7

• Image height
• Image width
• Geoloaction of the image’
• Date that the image was taken

Question 8

An image colour depth is…

Answer 8

The number of bits needed to store the colour of each pixel

Question 9

An image resolution is..

Answer 9

The number of pixels per inch. controls the fineness of detail of the image

Question 10

The file size of an image is reliant on…

Answer 10

Colour depth and resolution

Question 11

A computer sound file is created by measuring…

Answer 11

The height of a sound wave

Question 12

The sample rate is…

Answer 12

Taking measurements of the amplitude of the sound wave at regular intervals. The higher the sample rate, the higher the quality and file size

measured in Hz

Question 13

A computer sound file bit depth is…

Answer 13

The number of bits used to store each sample (each wave). The higher the bit depth, the closer the playback sound will be in quality to the original sound

Question 14

Compression is when…

Answer 14

A file reduces its size

Question 15

Lossy compression is when…

Answer 15

Data is removed from a file which reduces the file size more than lossless by removing less important data
This reduces the image quality but ofen it is unnoticeable

Question 16

Lossless compression is when…

Answer 16

Data is more efficiently stored
Used in text files as lossy can’t be used as none of the data can be removed otherwise it would mkae the file unreadable

Question 17

Name an image sound and movie example for lossy

Answer 17

JPEG mp3 and MPEG

Question 18

Name a text image sound and movie example for lossless

Answer 18

PDF gif flac and mp4

Question 19

How to calculate image file size

Answer 19

file size = bit depth x number of pixels

To find number of pixels, you do height x width

Question 20

How to calculate the size of a sound file

Answer 20

file size = bit depth x sample rate x duration of sound

Question 21

BEnefits of compression

Answer 21

• Takes up less space on servers
• Faster upload time to server
• FAster download for users

Question 22

What is an overflow error

Answer 22

• When a computer attempts to store something larger than 8 bits in a single byte
• This is often done when two 8 bit numbers are added together

Question 23

Differences between lossy and lossless compression

Answer 23

• The quality often decreases when using lossy compression but the quality is the sames as the original in lossless
• Lossless files can be decompressed to get the original but lossy files can’t be used to retrive the original
• Lossy compression greately reduces the file size more than lossless compression

Question 24

What happens to an image when you increase the resolution

Answer 24

• Image quality will improve as the image has more pixles so can show finer detail images
• Image file size will increase because there are more pixels to store

Question 25

Different ways of storing images and their properties

Answer 25

• Bitmap - image made up of different coloured squares with each square having a binary value
• Vector - the mathematics to draw the image is stored eg. the width and colour

Question 26

How is a sound recording taken

Answer 26

1. Analogue sound recieved by a microphone
2. This is converted into a digital form using an ADC
3. Sound is sampled at regular time intervals (sample rate)
4. The amplitude of the wave is stored as binary