02 Section 7 - Sound, Image and Compression

Question 1

How are images stored?

Answer 1

Images are stored as a series of pixels

-bitmap images are made up of pixels

Question 2

How do you have colour on an image?

Answer 2

The colour of each pixel is represented by a binary code

• black and white images only need 1 bit
• you can make a greater number of shades by increasing the number of bits per pixel

Question 3

Define colour depth:`

Answer 3

Colour depth is the number of bits used for each pixel

Question 4

How do you work out the number of colours you can get from the colour depth?

Answer 4

Total number of colours = 2^n

n = the number of bits per pixel

Question 5

What is the common colour bit depth?

Answer 5

24bit, so each colour(red, green, blue) have 1 byte each

Question 6

What is resolution measured in?

Answer 6

Resolution is the density of pixels in an image

-measured in dots per inch

Question 7

What does a higher resolution mean?

Answer 7

The higher the resolution, the more pixels in a certain area so the better quality of image.
-also increases the file size

Question 8

Define metadata:

Answer 8

Metadata is information stored in an image file which helps the computer recreate the image on screen from binary data in each pixel,

Question 9

What does metadata usually include?

Answer 9

file format, height, width, colour depth, resolution

Question 10

How is sound recorded by a microphone?

Answer 10

Sound is recorded by a microphone as an analogue signal

-analogue signals are pieces of continually changing data

Question 11

Can computers understand analogue signals?

Answer 11

No, analogue signals need to be converted into digital data

Question 12

How are analogue signals converted to digital data?

Answer 12

It’s converted by analogue to digital converters

-by a process called sampling

Question 13

What are some factors which affect size and quality of sound files?

Answer 13

Sampling intervals
Sampling frequency
Sample size
Bit rate

Question 14

What are sampling intervals?

Answer 14

gaps between each point when the analogue recording is sampled
-measured in ms

Question 15

What is sampling frequency?

Answer 15

how many samples you take per second

-measured in kHz

Question 16

What is sample size?

Answer 16

is the number of bits available for each sample

Question 17

What is bit rate?

Answer 17

the number of bits used per second of audio

-measured in kbits/s

Question 18

How do you calculate bit rate?

Answer 18

bit rate = sampling frequency x sample size

Question 19

How will increasing the sample size improve the quality of a sound file?

Answer 19

it will pick up quieter sounds, this will make the recording closer to the sound of the original

Question 20

What are the uses of compressing data files?

Answer 20

• smaller files take up less storage space
• streaming and downloading files from the internet is quicker(less bandwidth)
• web pages load quicker
• email services have restrictions on the size of attachment you can send

Question 21

What are the two types of file compression?

Answer 21

Lossy

Lossless

Question 22

Define Lossy compression:

Answer 22

it works by removing data permanently from the file

Question 23

Define Lossless compression:

Answer 23

it temporarily removes data by encoding it and then it restores it to its original state when it is opened

Question 24

What are the pros and cons of Lossy compression?

Answer 24

Pros
-greatly reduces file size
-takes up less bandwidth(download/streamed quicker)
Cons
-can’t return to original file(loses data permanently)
-can’t be used on text or software files

Question 25

What are the pros and cons of Lossless compression?

Answer 25

Pros
-no reduction in quality
-can be used for software and text files
Cons
-only a slight reduction on file size

Question 26

What are some examples of Lossy file types?

Answer 26

MP3
AAC (audio)
JPEG

Question 27

What are some examples of Lossless file types?

Answer 27

FLAC (audio)
TIFF (image)
PNG (image)