Question 9 (30%) a. Explain and distinguish between lossy and lossless compression. Include a brief description on each compression type, together with their relative merits and an example of each. (8 marks) b. Lempel-Ziv-Welch (LZW) is a commonly used lossless compression algorithm which is the basis of ZIP-file coding. i. Using the online (Block 2, Activity 2.2) LZW encoding tool, determine the LZW- encoded data for the following 14-character sequence: WOOLLOOMOOLOOL Include the Code Table entries as part of your answer. (2 marks) ii. The next part of the sequence (without any spaces) is the following 8 characters: @MOLOLOL Determine, by hand, what is the LZW-encoded data for this 8-character sequence by both using and updating the Code Table (dictionary) entries constructed in part (i). Include the updated Code Table as part of your answer. (12 marks) Part (ii) requires you to construct, by hand, a table like Table 2.18 (Block 2, Part 2, p. 120) with separate entries for each of the 8 characters comprising the new sequence. Include a copy of Line 13 from the LZW encoded sequence you have already obtained from the online tool. Hint: As there are no spaces, the Q-column entry in Line 14 of the online table will now be the first character (@) of the next part of the sequence. Note: do not simply copy the new 8-character sequence into the online LZW tool, as the Code Table you have created in Part (i) will be reset. c. Blu-ray optical disks use a combination of two different Reed-Solomon (RS) codes. One is the Long-Distance Code (LDC) while the other is the Burst Indicator Subcode (BIS). State the different roles these two RS codes perform. (2 marks) d. Explain what is respectively meant by the terms symbol errors and symbol erasures in RS coding. (2 marks) e. The RS(255, 239) byte code is widely used for error correction in Digital Video Broadcasting applications. Determine the following: i. How many symbol errors can this RS code correct? ii. How many symbol erasures can this RS code correct? In both cases, give the corresponding number of bits able to be corrected. (4 marks) Question 9 (30%) a. Explain and distinguish between lossy and lossless compression. Include a brief description on each compression type, together with their relative merits and an example of each. (8 marks) b. Lempel-Ziv-Welch (LZW) is a commonly used lossless compression algorithm which is the basis of ZIP-file coding. i. Using the online (Block 2, Activity 2.2) LZW encoding tool, determine the LZW- encoded data for the following 14-character sequence: WOOLLOOMOOLOOL Include the Code Table entries as part of your answer. (2 marks) ii. The next part of the sequence (without any spaces) is the following 8 characters: @MOLOLOL Determine, by hand, what is the LZW-encoded data for this 8-character sequence by both using and updating the Code Table (dictionary) entries constructed in part (i). Include the updated Code Table as part of your answer. (12 marks) Part (ii) requires you to construct, by hand, a table like Table 2.18 (Block 2, Part 2, p. 120) with separate entries for each of the 8 characters comprising the new sequence. Include a copy of Line 13 from the LZW encoded sequence you have already obtained from the online tool. Hint: As there are no spaces, the Q-column entry in Line 14 of the online table will now be the first character (@) of the next part of the sequence. Note: do not simply copy the new 8-character sequence into the online LZW tool, as the Code Table you have created in Part (i) will be reset. c. Blu-ray optical disks use a combination of two different Reed-Solomon (RS) codes. One is the Long-Distance Code (LDC) while the other is the Burst Indicator Subcode (BIS). State the different roles these two RS codes perform. (2 marks) d. Explain what is respectively meant by the terms symbol errors and symbol erasures in RS coding. (2 marks) e. The RS(255, 239) byte code is widely used for error correction in Digital Video Broadcasting applications. Determine the following: i. How many symbol errors can this RS code correct? ii. How many symbol erasures can this RS code correct? In both cases, give the corresponding number of bits able to be corrected. (4 marks)
