Multimedia gds MSc exam 2000 SOLUTIONS Setter: ADM Checker: AcJ Answer 3 Questions out of 4 Time allowed 2 Hours 1.(a)Why is data compression, including file compression, highly desirable for Multimedia activities? Multimedia files are very large therefore for storage, file transfer etc file sizes need to be reduced. Text and other files may also be encoded/compressed for email and other applications 2 MARKS--- BOOKWORK (b) Briefly explain, clearly identifying the diferences between them, how entropy coding and transform coding techniques work for data compression. Illustrate your answer with a simple example ofeach type Compression can be categorised in two broad ways ossless 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 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 Lossless compression frequently involves some form of entropy encoding and are based in information theoretic techniques Lossy compression use source encoding techniques that may involve transform encoding, differential encoding or vector quantisation ENTROPY METHODSMultimedia IGDS MSc Exam 2000 SOLUTIONS Setter: ADM Checker: ACJ Answer 3 Questions out of 4 Time Allowed 2 Hours 1. (a) Why is data compression, including file compression, highly desirable for Multimedia activities? Multimedia files are very large therefore for storage, file transfer etc. file sizes need to be reduced. Text and other files may also be encoded/compressed for email and other applications. 2 MARKS --- BOOKWORK (b) Briefly explain, clearly identifying the differences between them, how entropy coding and transform coding techniques work for data compression. Illustrate your answer with a simple example of each type. Compression can be categorised in two broad ways: 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. 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. Lossless compression frequently involves some form of entropy encoding and are based in information theoretic techniques Lossy compression use source encoding techniques that may involve transform encoding, differential encoding or vector quantisation. ENTROPY METHODS: