What is LZW compression? Explain with example.

Decoding the Magic of LZW Compression: A Data Compression Deep Dive

What is LZW Compression?

• Lempel-Ziv-Welch (LZW) is a lossless data compression algorithm.
• It works by replacing repeating sequences of data with shorter codes.
• It's widely used in GIF image format and other applications.
• Highly effective for data with repeating patterns.

How LZW Compression Works: A Step-by-Step Guide

• Starts with a dictionary containing single characters.
• Reads the input data character by character.
• Concatenates characters to form strings.
• When a string is not found, it's added to the dictionary with a new code.
• The code for the longest matching string is written to the output.
• This process continues until the entire input is processed.

LZW Compression Example:

• Initial Dictionary: {'A': 1, 'B': 2, 'C': 3}
• Input String: "ABABCABABCACC"
• Processing:

- 'A' is encoded as 1. - 'AB' is encoded as 4 (added to dictionary). - 'ABA' is encoded as 5 (added to dictionary). - 'ABAB' is encoded as 6 (added to dictionary). - 'C' is encoded as 3. - 'ABAB' is encoded as 6. - 'CACC' is encoded as 7 (added to dictionary).

• Compressed Output: 1, 4, 5, 6, 3, 6, 7

Decompression:

• Uses the dictionary to reverse the encoding process.
• Reads the codes from the compressed data.
• Looks up the corresponding strings in the dictionary.
• Reconstructs the original string.

Advantages of LZW Compression

• Lossless compression—no data is lost.
• Adaptive—the dictionary grows dynamically.
• Relatively simple to implement.

Disadvantages of LZW Compression

• Can be slower than some other methods.
• Requires significant memory for the dictionary.