MM_BSC_SOLNS_2008

MM_BSC_SOLNS_2008 - CM0340SOLNS CARDIFF UNIVERSITY...

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Unformatted text preview: CM0340SOLNS CARDIFF UNIVERSITY EXAMINATION PAPER Academic Year: 2007/2008 Examination Period: Autumn Examination Paper Number: CM0340SOLNS Examination Paper Title: Multimedia SOLUTIONS Duration: 2 hours Do not turn this page over until instructed to do so by the Senior Invigilator. Structure of Examination Paper: There are 13 pages. There are 4 questions in total. There are no appendices. The maximum mark for the examination paper is 80 and the mark obtainable for a question or part of a question is shown in brackets alongside the question. Students to be provided with: The following items of stationery are to be provided: ONE answer book. Instructions to Students: Answer 3 questions. The use of translation dictionaries between English or Welsh and a foreign language bearing an appropriate departmental stamp is permitted in this examination. 1 PLEASE TURN OVER CM0340SOLNS Q1. (a) Why is data compression desirable for multimedia activities? Data is high resolution in both temporal and/or spatial domains. [1] Storage, bandwidth and processing limitations need compressed data. [1] 2 Marks total BOOKWORK (b) What is the distinction between lossy and lossless data compression? Lossless Compression Where data is compressed and can be reconstituted (uncompressed) without loss of detail or information. These are referred to as bit-preserving or reversible compression systems also. [1] Lossy Compression Where the aim is to obtain the best possible fidelity for a given bit-rate or minimizing the bit-rate to achieve a given fidelity measure. Video and audio compression techniques are most suited to this form of compression. [1] 2 Marks total BOOKWORK (c) What are the main differences between the target media for JPEG and GIF com- pression? JPEG 24 bit full/true colour imagery, typically photographic in nature. [1] GIF 8-bit colour imagery, suits graphics type images better. [1] 2 Marks total BOOKWORK (d) What improvement did the LZW algorithm make on previous LZ versions? LZW introduced the idea that only the initial dictionary needs to be transmitted to enable decoding . [1] The decoder is able to build the rest of the table from the encoded sequence. [1] 2 Marks total BOOKWORK 2 CM0340SOLNS (e) Describe the LZW algorithm for encoding an input sequence, giving suitable pseudocode. The LZW Compression Algorithm can summarised as follows: w = NIL; while ( read a character k ) { if wk exists in the dictionary w = wk; else { add wk to the dictionary; output the code for w; w = k; } } [6] May have a prior dictionary Original LZW used dictionary with 4K entries, first 256 (0-255) are ASCII codes. GIF builds dictionary of image blocks no priors....
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MM_BSC_SOLNS_2008 - CM0340SOLNS CARDIFF UNIVERSITY...

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