Question Sheet 1

Multimedia Data Delivery –AV Representation and Data Coding By John Cosmas

1. In a PAL system, determine the values of the three colour primaries R, G and B for the following colours: red, green, blue, yellow, cyan, magenta and white.

2. Calculate the luminance and chrominance values of the colours in problem 1, if they are digitised into eight bits according to CCIR-601 specification.

3. Describe what is meant by the spatial frequency response and the temporal frequency response of the eye and explain the implications of these characteristics on the design of television systems.

4. a) A CCIR 601 image has 625 active scan lines and 23 inactive lines at 25 frames per second and an aspect ratio of 4:3 over all scan lines (active and inactive). Calculate: i) the bit rate per second for a system that uses 4:2:0 colour subsampling with 8 bits for luminance, 8 bits for Red and 8 bits for Blue; ii) the bit rate per second for a system that uses 4:2:2 colour subsampling with 8 bits for luminance, 8 bits for Red and 8 bits for Blue; iii) the resultant bit rate for (i) with a codec which provides 97% compression. iv) the resultant bit rate for (ii) with a codec which provides 97% compression.

5. Describe what happens to an analogue signal in the frequency domain when it is sampled. Explain how this phenomenon is used to transmit both the colour and luminance signals in analogue TV broadcast systems. 6. Explain the difference between single-pass and dual-pass entropy encoding and describe an example of each of these techniques in data coding. 7. The intervals of an arithmetic coder of strings a, b, c, and d are [0.0, 0,2), [0.2, 0.7), [0.7, 0.95), and [0.95, 1.0) respectively. Suppose the arithmetic coder receives 0.83955. Decode the first three symbols of the message. Explain what is meant by the entropy of a sequence of stationary symbols. 8. A soft drinks machine vendor sells soft drinks with a relative frequency of occurance listed in Table Q1. Calculate what is the entropy of this symbol sequence and relate this result to the Huffman coding scheme.

Drink Frequency of Occurance Coke 8 Fanta 4 7-Up 2 Sprite 1 Tango 1 Table Q1