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1. Computer Science
CIE-Syllabus 2210
Lesson 21
Compression of Image
files.
Tutor: Suraj Motee

2. Learning Outcomes
• Explain how images can be compressed.

3. What is compression?
• Compression is the process of encoding information using
fewer bits so that the compressed file size is smaller.

4. Types of compression
Lossless Lossy

5. LOSSLESS COMPRESSION
Original
100 MB
Compressed
50 MB
Restored
100 MB
LOSSLESS COMPRESSION can reduce file size without losing quality.

6. LOSSY COMPRESSION
Original
100 MB
Compressed
50 MB
Restored
80 MB
LOSSY COMPRESSION removes unnecessary information and redundant data so as to reduce the size of
the file.

7. IMAGE COMPRESSION
Reducing
image quality
Removing
Repetition

8. Reducing image quality
An image file is made up of pixels.
The total number of pixels make up the image resolution(
Number of pixels by width x Number of pixels by height)
Reducing number of pixels and the number of bits required
to store each pixel color) will reduce file size.

9. Remove repetition
The 2 dimensional representation of this image is:
B R R
G G B
B B B
Repetition can be removed:
B R2
G2 B
B3