Specification Journal 012
3.5.6 Representing images, sound and other data
For this specification point the following areas are covered: (3.5.6)
 3.5.6.1 Bit patterns , images sound and other data
 3.5.6.2 Analogue and digital
 3.5.6.3 Analogue Digital Conversion
 3.5.6.4 Bitmapped graphics
 3.5.6.5 Digital representation of sound
 3.5.6.6 Musical Instrument Digital Interface (MIDI)
 3.5.6.7 Data Compression
 3.5.6.8 Encryption
1.1 Key terms to define
Write a detail definition of each term given below. Look into the technical aspects of each key
word.
Term
Definition
Bit-mapped graphic
Pixel
Resolution
Colour depth
Vector graphic
Analogue
Digital Signal
Compression
Run-length
encoding
Dictionary based
encoding
Lossless
Compression
Lossy Compression
Encryption
Decryption
Plaintext
Ciphertext
Questions to complete
1.2 Bitmaps
1) What is a bitmapped graphic? (2)
2) Complete the follow table below to work out memory requirements for different displays. You
will have to investigate some of the figures. (21)
Resolution Name
CGA
VGA
SVGA
HD Ready
Full HD
4K
8K
Resolution
Colour Depth
MB required
3) What does metadata mean and how does it apply to bitmaps? (2)
1.3 Analogue to Digital Conversions
1) Analogue produces a purer sound than digital. Discuss why this example could be true using
examples. (4)
1.4 MIDI
1) What is the purpose of MIDI? (4)
2) What are event messages in MIDI and what are they used for? (4)
3) What is the advantage of using MIDI files over other digital audio formats? (4)
1.5 Representation of sound
1) What is the sampling rate in relation to digitally representing sound? (4)
2) What is the sampling resolution in relation to digitally representing sound? (4)
3) What is Nyquist’s theorem? (4)
4) Referring to Nyquist theorem, why are CD’s sampled at 44,100hz? (4)
6) Describe the process that an ADC undertakes in order to digitally represent a sound wave. (4)
7) How much memory would a CD quality version of Queen’s famous song “Bohemian Rhapsody”
take up? (4)
1.6 Compression
1) Research one of the better known compression file types and find out what compression
algorithm is used. (4)
2) Research the LZ77,LZ78 and LZW compression methods (4)
3) Using a bitmap image and fireworks – demonstrate how making it a jpeg compresses the file size.
Discuss the difference between the images and what actually happened. (4)
4) What is a CODEC? (4)
5) Describe using different examples from the video how Run-Length Encoding and Dictionary based
compression works. (4)
6) Run length coding (RLE) is a pattern substitution compression algorithm. Data is stored in the
format (colour, run). Reassemble the following data in a 7X7 grid. (4)
(0,1),(1,5),(0,1)
(1,7)
(1,1),(0,2),(1,1),(0,2),(1,1)
(1,7)
(0,1),(1,1),(0,1),(1,1),(0,1),(1,1),(0,1)
(0,1),(1,1),(0,1),(1,1),(0,1),(1,1),(0,1)
(0,1),(1,1),(0,3),(1,1),(0,1
7) What are the advantages and disadvantages of both Lossless and Lossy methods of compression?
(4)
1.7 Encryption
1) What is the Enigma machine and what was its significance? (4)
2) Describe what a polyalphabetic cipher is using an example. (4)
3) Describe what a Rail fence cipher is using an example. (4)
4) Describe what a Route Cipher is using an example. (4)
5) The Vernam cipher uses a one-time pad. What is meant by a one-time pad? (4)
6) Using ASCII code – apply the one-time pad £]FL to the word exam. Encrypt it using the Vernam
method. (4)
7) What is Computational security? (4)
8) Why is the Vernam Cipher said to be mathematically unbreakable? (4)
9) What conditions must be met for a Vernam Cipher to be 100% Secure (4)
10) What are some of the methods cryptographers can use to crack codes? (4)
11) Create a C# program that simulates the Vernam cipher by allowing you to enter in the one-time
pad and the plain text and then encrypts it. Extend this by getting the program to generate the
random key itself the length of the plain text entered. (10)