1. File Compression
3.3

2. Learning Objectives
3.3.2 Understand the need for data compression and methods of compressing data [lossless, lossy] and that JPEG and MP3 are examples of lossy algorithms
3.3.3 Understand how a lossless, run-length encoding [RLE] algorithm works
3.3.4 Understand that file storage is measured in bytes and that data transmission is measured in bits per seconds, and be able to calculate the time required to transmit a file and storage requirements for files

3. Transfer Rate Why compress data?
If you have 10 high quality images at 4Mb’s each. How much storage will it take up?
What if you were to transfer this data across the internet, how would you calculate the transfer rate, what is it measured in?
Transfer rate (Mbps) = Number of files * file size / time taken * 8

4. What do we already know? What is colour depth?
How many colours can be represented using 4 bits?
What are the differences between bitmap images and vector images?

5. Answer the following in a word.doc
Use BBC Bitesize to help you:
Google bbc bitesize compression
Why compress an image?
What are 2 compression methods?
What are at least 3 advantages and disadvantages of these 2 compression methods?

6. Understanding Images Music
Images Music
Lossless Lossless
PNG WAV
Lossy Lossy
JPEG MP3
GIF AAC

7. Lossless Algorithm
A A B A A A
2B2
2B3
2B1 2 1 2B

8. Run Length Encoding 3 bananas 2 Strawberries 1 banana 1 pineapple
3B, 2S, 1P, 1B

9. Activity
1, 3, 1
4, 1

10. Explanation https://www.youtube.com/watch?v=Lto-ajuqW3w 2:30-6:43

11. Plenary Why compress images?
What are the two main ways to compress images?
Name some of the differences
Outline the RLE algorithm
What compression method would you use when uploading an image to Facebook?