Run length encoding and dictionary coding for lossless compression.

• lossless compression works by removing redundancy ‘#

two key ways are

• run length encoding

• dictionary coding

🔵 1. Run Length Encoding (RLE)

💡 Idea (very simple)

If data repeats, instead of storing it again and again, we store:

👉 the value + how many times it repeats

Example

Original data:

AAAAABBCCCC

RLE:

5A2B4C

👉 Instead of writing A five times, we say “5A”

”

🧠 Why it works

It is effective when:

• There are lots of repeated values

It is bad when:

• Data has little or no repetition

Example:

ABCDEFG

RLE might actually make it longer.

🔴 2. Dictionary Coding

💡 Idea (simple)

Instead of repeating long patterns, we:

1. Store patterns in a dictionary

2. Replace them with short references (indexes)

Example

Original:

the cat sat on the mat and the cat ran

Dictionary:

1 = the  
2 = cat  
3 = sat  
4 = on  
5 = mat  
6 = and  
7 = ran

Encoded:

1 2 3 4 1 5 6 1 2 7

👉 Repeated words are replaced with short numbers