Compression
- Compression reduces the size of files to save storage space and speed up data transmission.
- There are two main types of compression: lossless and lossy.
Note
- Lossless compression is used when it is important to retain the original data.
- Lossy compression is used when some data loss is acceptable in exchange for greater compression.
Lossless Compression
Definition
Lossless compression
Lossless compression runs an algorithm to compress the data, the algorithm can then be reversed to restore the data. This ensures that the original data can be perfectly reconstructed from the compressed version.
How Lossless Compression Works
Lossless compression algorithms find patterns and redundancies in the data and encode them more efficiently.
Example
- Run-Length Encoding (RLE): Replaces repeated characters with a single character and a count.
- i.e, "AAAAABBBCC" becomes "5A3B2C."
- Huffman Coding: Assigns shorter codes to more frequent characters and longer codes to less frequent characters.
- Lempel-Ziv-Welch (LZW): Builds a dictionary of patterns in the data and replaces repeated patterns with shorter codes.
Advantages of Lossless Compression
- No Data Loss: The original file can be perfectly reconstructed.
- Suitable for Critical Data: Used for text, software, and other files where data integrity is essential.
Disadvantages of Lossless Compression
Lower Compression Ratios: Lossless compression typically achieves lower compression ratios compared to lossy compression.
Example
- Compressing a text file using ZIP reduces its size by 50%.
- When decompressed, the original text is restored without any loss.
Lossy Compression
Definition
Lossy compression
Lossy compression reduces file size by discarding some data that is less noticeable or redundant, resulting in an approximation of the original content.
How Lossy Compression Works
Lossy compression algorithms identify data that can be safely discarded or approximated.
Example
- JPEG (Images): Removes high-frequency details that are less noticeable to the human eye.
- MP3 (Audio): Discards frequencies that are outside the range of human hearing.
- MPEG (Video): Reduces color depth and resolution in areas with less motion.
Advantages of Lossy Compression
- Higher Compression Ratios: Lossy compression can achieve much higher compression ratios than lossless compression.
- Smaller File Sizes: Ideal for images, audio, and video where some data loss is acceptable.
Disadvantages of Lossy Compression
- Data Loss: The original file cannot be perfectly reconstructed.
- Quality Degradation: Repeated compression and decompression can lead to noticeable quality loss.
Example
- Compressing a 5 MB image using JPEG reduces its size to 500 KB.
- The compressed image looks similar to the original, but some details are lost.
Key Differences Between Lossless and Lossy Compression
| Feature | Lossless Compression | Lossy Compression |
|---|---|---|
| Data Integrity | No data loss | Some data loss |
| Compression Ratio | Lower | Higher |
| Use Cases | Text, software, critical data | Images, audio, video |
| Reversibility | Reversible | Irreversible |
