23 Questions
What is the purpose of RLC (Run-Length Coding)?
To encode the symbol and the length of the group
What is the main idea behind Variable Length Coding?
Techniques based on the entropy ideas
How do you construct a Shannon-Fano tree?
By adding a '0' when going left to a child and adding a '1' when going right
What is the formula to calculate the entropy (η) of characters?
η = -∑pi log2(pi)
What is the formula to calculate the average number of bits needed for each character?
Average bits = Total bits / Total characters
What is the Compression Ratio formula?
Compression Ratio = B0 / B1
What is the purpose of drawing a Shannon-Fano tree?
To construct a binary tree for encoding characters
What is the distribution of characters in Shannon-Fano coding?
Symbol distribution
What is the primary advantage of digital representation of video signal?
It can be stored on digital devices or in memory
Which of the following statements about video scanning is true?
Progressive scanning is used in CRT monitors
What is the purpose of compression ratio?
To compare the number of bits before and after compression
What is entropy in the context of information theory?
A measure of the information contained in a source
What is the purpose of defining entropy?
To specify the lower bound for the average number of bits to code
What is the difference between lossless and lossy compression?
Lossless compression reduces the size of files without losing information, while lossy compression reduces the size of files with some information loss
What is the formula for compression ratio?
Compression ratio = B0 / B1
What is the primary advantage of digital representation of video signal in terms of repeated recording?
Image quality does not degrade
What is the compression ratio for the input string 'ABABBABCABABBA' using LZW compression?
1.56
What is the output code for the input string 'ZWZWWZW' using LZW compression, given the initial dictionary (Z=1, W=2)?
1 2 3 4 2
What is the compression ratio for the input string 'ZWZWWZW' using LZW compression, given the initial dictionary (Z=1, W=2)?
1.4
What is the purpose of the LZW decompression algorithm?
To decompress data
What is the output string for the input code '1 2 4 5 2 3 4 6 1' using LZW decompression, given the initial dictionary (A=1, B=2, C=3)?
ABABBABCABABBA
What is the output string for the input code '1 2 3 4 2' using LZW decompression, given the initial dictionary (Z=1, W=2)?
ZWZWWZW
How many bits are needed to encode the message '(BCA)' using Arithmetic coding, given the probability distribution of the alphabet (A, B, C)?
6
Study Notes
Video Scanning
- Progressive scanning traces a complete picture (a frame) for each time interval.
- CRT Monitor uses progressive scanning with a minimum refresh rate of 85Hz.
- Interlaced scanning is used in TVs.
Digital Representation of Video Signal
- Digital video is represented as a sequence of digital images.
- Advantages of digital representation:
- Video can be stored on digital devices or in memory.
- Video is ready to be processed (noise removal, cut and paste, etc.).
- Video can be integrated into various multimedia applications.
- Repeated recording does not degrade image quality.
- Ease of encryption.
Compression
- Compression: process of coding to reduce the number of bits needed for information.
- Two main categories of compression:
- Lossless: input message = output message.
- Lossy: input message ≠output message.
Data Compression Scheme
- Compression ratio: B0 / B1, where B0 is the number of bits before compression and B1 is the number of bits after compression.
Entropy
- Entropy (): a measure of the information contained in a source.
- Entropy is used to find the optimal code.
- ≠specifies the lower bound for the average number of bits to code.
Run-Length Coding (RLC)
- RLC: code one symbol and the length of the group.
- Example: ABBCCDDDDDDDEEFGGGGG can be encoded as ABBCCD#9EEFG#5, reducing 22 characters to 14 characters (36% reduction).
Variable Length Coding
- Techniques based on entropy ideas.
- Two techniques: Shannon-Fano and Huffman coding.
- Variable length coding creates a binary tree.
- To read the codes, start from the root, adding '0' when going left and '1' when going right.
Shannon-Fano Tree
- Used to encode characters based on their probability distribution.
- Calculate the average number of bits needed for each character and the compression ratio.
LZW Compression
- Dictionary-based LZW compression algorithm.
- Shows the dictionary and output for LZW compression of an input string.
- Compression ratio is calculated.
LZW Decompression
- Dictionary-based LZW decompression algorithm.
- Shows the dictionary and output for LZW decompression of an input code.
- Output string is the original input string.
This quiz covers the concepts of progressive scanning, digital representation of video signals, and their advantages in multimedia applications.
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