Component 1.9 Security and Data Management Compression

Complete the Entry Ticket on Compression Starter: Entry Ticket Complete the Entry Ticket on Compression Extension: Explain using examples how video and image files can be compressed using lossy and lossless compression.

Learning Intentions and Outcomes To develop an understanding of how data is compressed to reduce the filesize Grade 4 Explain the term compression and its purpose Identify appropriate methods of compression for various digital products Grade 5-6 Explain using examples how lossy and lossless compression are used Explain using examples whether lost or lossless compression is the most appropriate for reducing the filesize of given digital products Grade 7 Analyse the importance of compression Evaluate scenarios to identify the best method of compression for a given digital product

Assessment Outcomes Explain how lossy and lossless data compression algorithms are used Calculate compression ratios

Starter Discussion Two types of compression: Lossy Lossless Lossy compression is used when it doesn’t matter if some of the quality is lost. For example a photograph or a video – you can lose a little quality and the product will still fulfil its intended purpose. Lossless compression is used when no information can be lost. For example when compressing the source code of a program! If you lost some of the source code the program may not function!

Starter Discussion The purpose of compression is to reduce the file size of a digital product. This may be so that it can be sent over a network quicker or so that it takes up less space on a hard drive.

Compression Purpose: Reduce file size Mostly used with sound, image and video file types Two types: Lossy compression (JPG, GIF, MP3) Lossless compression (PNG, TIF, SVG)

Lossy compression Permanently removes some data Recreates the file using the remaining data and uses algorithms to guess the removed content Uncompressed data is not the same as the original Would this technique work for compressing a computer program?

How lossy compression works Similarly coloured pixels are all made the same

Lossless image compression Finds groups of repeating data and records the data only once along with the number of times it was repeated = 12 x + 6 x When data is uncompressed it is restored exactly as it was in the original

Lossless text compression Finds patterns in the original text Encodes each pattern in a dictionary An eye for an eye, a tooth for a tooth . 0000 An_ 1 0001 eye 2 0010 _for_ 3 0011 an_ 4 0100 ,_ 5 0101 a_ 6 0110 tooth 7 0111

Lossless text compression 38 Characters including spaces = 38 bytes (assuming an 8-bit ASCII table is used) 48 bits = 12 bytes = 32% of original size (plus codes) . 0000 An_ 1 0001 eye 2 0010 _for_ 3 0011 an_ 4 0100 ,_ 5 0101 a_ 6 0110 tooth 7 0111 1 2 3 4 5 6 7 0001 0010 0011 0100 0101 0110 0111 0000

Transmission of data over IP Why use compression? Download speeds are increased Data allowances are reduced Voice can be transmitted fast enough to keep up with speech

Downloading a music track Dancing Queen by ABBA = 3m 51sec = 231 seconds MP3 quality = 128kbps CD quality = 1411kbps 231 x 128kbps = 29,568kbs / 1024 / 8 = 3.6MB OR: 231 x 1411kbps = 325,941kbs / 1024 / 8 = 39.79MB 11.5 times faster with a compressed file 36MB less download data used

Benefits of compression Smaller files = fewer packets = faster transmission Quicker to complete Reduces traffic over the Internet Less chance of collisions or transmission errors Improves download speed of video, sound (including speech used for VOIP systems) and image files Speeds up download of webpages that use images Reduces space on disk / servers Enables better streaming of music and video

Common file standards PDF – Fixed layout document that maintains its original appearance regardless of the software used to view it JPG – Lossy compressed files commonly used for website images GIF – Lossy compressed images using only 256 colours, used for simple web graphics PNG – Lossless compressed format using an alpha channel to preserve transparent backgrounds MP3 – Lossy music format

Grade 4: Compression Define the term compression Put the subtitle “Compression” in your book and answer the Grade 4 Exercises Extension Move on to the exam questions at the front of the room Define the term compression Explain the difference between the two compression techniques (lossy and lossless) Identify which compression technique is most appropriate for the following, giving examples to explain why for each: Source Code Word Document containing a Script for a film Database containing customer information Family photo from holiday – to be printed and put on a wall Selfie to upload to Facebook Short video clip to share on Instagram

Grade 5-7 Exam Questions Complete them Self Assess them Stick them in Bring them to me

Grade 8 Extension Look in the A-Level folder and complete the Grade D exercises about disaster planning and recovery.

Exit Ticket Complete the Exit Ticket and Stick it in your books.

Homework Graded Exercises Complete up to your Year 11 target grade in the graded exercises. Pre-Reading Pages 78-79 Lossy and Lossless compression