1.3.1 Compression, Encryption and Hashing

Question 1

Lossy Compression

Answer 1

A compression scheme where their generally involves a loss of resolution in parts of the image where experiences shows that it will be least noticed.

Question 2

Lossless Compression

Answer 2

A compression scheme that allows the original images to be recreated.

Question 3

Length Encoding

Answer 3

A very simple form of data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run.

Question 4

Dictionary Coding

Answer 4

A class of lossless data compression algorithms which operate by searching for matches between the text to be compressed and a set of strings contained in a data structure (called the ‘dictionary’) maintained by the encoder.

Question 5

Symmetric Encryption

Answer 5

The oldest and best-known encryption technique. A secret key, which can be a number, a word, or just a string of random letters, is applied to the text of a message to change the content in a particular way. This might be as simple as shifting each letter by a number of places in the alphabet

Question 6

Asymmetric Encryption

Answer 6

This method of encryption involves using a pair of keys to encrypt and decrypt a message so that it arrives securely. Initially, a network user receives a public and private key pair from a certificate authority.

Question 7

Hashing

Answer 7

The process of calculating a numeric value from one or more data items. While this value obviously depends on the value of the data items, it need not depend on the meaning attached to themn, simply producing a number that is used within the computer.