Chapter 4, Exchanging data Video Solutions, AS and A Level OCR Computer Science

Problem 1

(a) Explain why compression is considered necessary for images on the web.
(b) Explain why lossy compression techniques would not be suitable for use with files containing large bodies of text.
(c) Suggest a suitable lossless method for compressing text.

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04:55

Problem 2

(a) Explain the difference between lossy and lossless data compression.
(b) Run-length encoding (RLE) is a pattern substitution compression algorithm. Data is stored in the format (colour,run), where $0=$ White and 1 = Black.
a. $(0,1),(1,5),(0,1)$,
b. $(1,7)$,
Reassemble the encoded sequence above to form a $7 \times 7$ web icon image in the grid below.
(c) RLE encoding is a lossless compression method. Give one disadvantage of lossless compression over lossy methods for the compression of images.
c. $(1,1),(0,2),(1,1),(0,2),(1,1)$,
d. $(1,7)$,
e. $(0,1),(1,1),(0,1),(1,1),(0,1),(1,1),(0,1)$,
f. $(0,1),(1,1),(0,1),(1,1),(0,1),(1,1),(0,1)$,
g. $(0,1),(1,1),(0,3),(1,1),(0,1)$
Reassemble the encoded sequence above to form a $7 \times 7$ web icon image in the grid below.

Stanley Enemuo

Numerade Educator

01:44

Problem 3

(a) State what is meant by symmetric encryption and explain with the aid of an example how it can be implemented.
(b) (i) Explain what is meant by asymmetric encryption.
(ii) Explain why this form is more(a) State what is meant by symmetric encryption and explain with the aid of an example how it can be implemented.
(b) (i) Explain what is meant by asymmetric encryption.
(ii) Explain why this form is more secure than symmetric encryption. secure than symmetric encryption.

Rachel Vallejo

Numerade Educator