fundamentals of data representation

Question 1

what is a pixel

Answer 1

• pixels are short for picture element
• the smallest identifiable area of an image
  -each pixel is a single colour and is given a binary value which represents that colour

Question 2

what is the resolution

Answer 2

the concentration of pixels within a specific area

Question 3

how many values does a one-bit-per-pixel allow

Answer 3

2 values - black and white

Question 4

how many colours come from 3 bits

Answer 4

8 - 2^8

Question 5

how does a higher bit depth affect the image

Answer 5

gives a greater quality of image and greater range of colours

Question 6

how many colours come from 24 bits

Answer 6

2^24 = 16777216

Question 7

how does the number of colours affect file size

Answer 7

an increase in the number of colours used( the bit depth ) increases the file size

Question 8

how does the size of the image affect file size

Answer 8

• an increase in the number of pixels in the image will increase the file size

BUT if the image’s physical size is increased by making each pixel larger, the file size will not change

Question 9

what is the formula to calculate the image file size in bits

Answer 9

width x height x colour depth

Question 10

what is the formula to calculate the image file size in bytes

Answer 10

width x height x colour depth / 8

Question 11

what is metadata

Answer 11

is data about data

Question 12

what are the ways to store images

Answer 12

bitmap and vector

Question 13

what is colour depth

Answer 13

the number of colours needed to represent each pixel

Question 14

sound is —– and must be converted to a ———– form for storage and processing in a computer

Answer 14

digital , digital

Question 15

what does ADC stand for

Answer 15

analogue to digital converter

Question 16

what is an ADC used for

Answer 16

to convert inputs to digital signals

Question 17

what is a DAC

Answer 17

digital to audio converter

Question 18

what does a DAC do

Answer 18

convert digital signals to outputs

Question 19

how is sound sampled

Answer 19

using a sample resolution ( bit depth)
- using a sampling rate

Question 20

what is sample resolution

Answer 20

the number of bits used to record each measurement

Question 21

what is the sample rate

Answer 21

The number of samples taken in a second is usually measured in hertz (1 hertz = 1 sample per second).

Question 22

what affects the quality of a digitally converted sound wave

Answer 22

sample rate and sample resolution

Question 23

what would happen if either or both sample rate or sample resolution increased

Answer 23

the quality of overall sound would also increase( get better ) and the file size will increase

Question 24

how to calculate file size (in bits) in term of sound

Answer 24

sampling rate x resolution x duration

Question 25

how can you improve the recording quality

Answer 25

• the more frequently we sample the sound
• the more accurately we record the wave height

Question 26

why is data compressed

Answer 26

• compression reduces the size of the file, so it takes up less space, and so you can maximise the amount of storage on a device
• smaller files are quicker when transferred / streamed over the internet

Question 27

what are some compression techniques ( images )

Answer 27

• to make the file size smaller: store a lower number of colours
• or store bigger areas of pixels as one colour

Question 28

what is lossy compression?

Answer 28

removes the data permanently, so the file can never return to its original form. ​

Question 29

what is lossless compression

Answer 29

Compression that doesn’t lose any of the file’s original quality

Question 30

what are some examples of lossy compression

Answer 30

JPG , GIF , MP3

Question 31

what are some examples of lossless compression

Answer 31

PNG, TIFF

Question 32

what is decompression

Answer 32

process where compressed data is resotred to its original format

Question 33

what does RLE stand for

Answer 33

run - length - encoding

Question 34

differences between lossy and lossless compression

Answer 34

lossy :
- some of the data is lost and cannot be recovered
-greatly reduces file size
-reduces the quality of the image/sound
- suitable for image and sound
- cannot be used on text and executable files

lossless:
- none of the data is lost , it is encoded differently
- can be turned back into original format
- can be used on all types of data
- less effective than lossy and reducing file size
- suitable on documents

Question 35

what is RLE used for

Answer 35

compressing bitmaps images

Question 36

Explain how data can be compressed using run length encoding

Answer 36

RLE uses frequency data pairs to to encode each run length of the same coloured pixel

Question 37

what type of compression is huffman coding

Answer 37

lossless