File formats

Question 1

[PPQ] How is a vector graphic represented?

Answer 1

Images are composed of a collection of geometrical objects, which have properties such as size, position, colour and shape

Question 2

[PPQ] How does run length encoding work?

Answer 2

The number of consecutive pixels of the same colour (the run) is counted, and pairs of values are stored, which consist of the pixel’s colour and the number of times it appears consecutively

Question 3

[PPQ] Why could RLE not compress a full colour image of a forest as well as it could compress a simple, 2-colour logo?

Answer 3

The image contains many different colours which don’t often appear multiple times consecutively, meaning the runs will be of shorter length, and the size of the run values will cancel out the reduction in size due to the compression

Question 4

[PPQ] Why can a 14kHz sound not be represented in digital form with a sample rate of 20kHz?

Answer 4

Nyquist’s theorem states that the sample rate must be at least twice the frequency of the highest sound in the original signal, and 20kHz is less than double 14kHz

Question 5

[PPQ] How does MIDI represent music?

Answer 5

Music is represented as a series of “event messages” which are 2-3 bytes long, which contain information such as instrument, note, duration of note, channel, etc.

Question 6

[PPQ] What are the advantages of MIDI?

Answer 6

The song is easy to modify (it’s easy to change the pitch and duration of notes), better quality because no background sound is recorded

Question 7

[PPQ] Explain the key difference between lossless and lossy compression methods

Answer 7

Lossless methods: No data is lost, can be reversed

Lossy methods: Some data is permanently lost and the encryption cannot be reversed