Run-Length Encoding Explained Step by Step

• 5A2B4C2D

This representation uses fewer characters than the original sequence, achieving compression.

Applying Run-Length Encoding to Images

RLE is often used with bitmap images, where:

• Large areas contain the same colour
• Pixels are stored row by row

For example, a row of pixels like:

• white, white, white, white, black

Can be encoded as:

• 4 white, 1 black

This is why RLE works well for:

• Simple images
• Icons
• Diagrams
• Images with large uniform areas

It performs poorly on complex photographs with lots of variation.

When Run-Length Encoding Is Effective

RLE works well when:

• Data contains many repeated values
• There are long runs of identical data
• The data is relatively simple

It is commonly used for:

• Simple graphics
• Black-and-white images
• Fax transmissions

When Run-Length Encoding Is Inefficient

RLE is ineffective when:

• Data changes frequently
• There are few repeated values
• Runs are very short

In these cases, RLE can even increase file size.

How Run-Length Encoding Appears in IB Exams

IB exam questions may ask students to:

• Encode a given sequence using RLE
• Decode an RLE sequence
• Explain why RLE is suitable or unsuitable
• Compare RLE to lossy compression

Clear, step-by-step working is essential for full marks.

Common Student Mistakes

Students often:

• Forget that RLE is lossless
• Encode individual values instead of runs
• Apply RLE to unsuitable data
• Skip steps in explanations

Examiners reward clarity and method.

Final Thoughts

Run-length encoding is a simple but powerful example of lossless compression. Its effectiveness depends entirely on the structure of the data being compressed. When applied correctly, it reduces file size without losing any information.

Understanding how RLE works step by step helps IB Computer Science students master compression questions confidently and accurately.

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