2. Common file formats  Lesson Objective: Understanding common file formats and their differences.  Learning Outcome:  Describe the type of files which are stored as: JPG, GIF, PDF, MP3, MPEG and ZIP Keywords: file format, image, sound, compression, lossy, lossless

3. Problem with image files …  They contain a lot of information  They can take up a huge amount of space  Without a method of compression a camera could only hold a few pictures  Without compression it would take ages to download a single photo from the internet.

4. Review: Storing images as pixels

5. Simple example: 2 bits per pixel Image is 8 bits by 11 bits The binary data is stored and the images can be reconstructed from this.

6. What do different colour depths look like? 1 bit (2 colour)4 bit (16 colours)8 bit (256 colours)24 bit (16 M colours)

7. Each pixel is stored in three bytes.

8.  The file size is BIG but with compression you can reduce the size

9. Choosing colours…  http://html-color-codes.info/

10. Lossy Compression  Lossy compression changes the original image, most of the time the changes are very subtle and are very hard to see.  The amount of compression can be varied to make the image better or worse.

11. Lossy Compression

13. Lossless compression  With lossless compression the original image is not changed, but this can mean that the amount of compression is not as good as lossey.

14. Animated image files

15. Image format wars!

16. Image file formats GIF Graphics Interchange File JPEG Joint Photograph Experts Group PNG Portable Network Graphics BMP Bit Map LosseyNoYesNo Can animateYesNo Transparency ? YesNoYesNo CommentsLow colour depth so best used for clipart Excellent compression, most common format for photos Similar to JPEG but allows transparency and is lossless. Uncompressed and results in a large file size. Only used for small images.

17. Other file formats PDF = Portable Document File This file format is used to share mainly text files, it works on many different operating systems (e.g. Windows, MacOS, Android..etc.) The software to read these files is free

18. MPEG MPEG = Motion Picture Experts Group Similar to JPEG but used in animation. It is a lossy file format but with a very good compression ratio. Free mpeg viewers are widely available over the internet and they work on a variety of operating systems.

19. MP3 MP3 = Motion Picture Experts Group Layer-3 Audio A very good lossey audio compression file format. There are changes to the original sound file which can be heard over good sound equipment but it is very subtle. MP3 files can be played on virtually all portable music players and operating systems.

20. Zip One or more files can be moved into a ZIP folder. You can save almost any file type in a ZIP folder and send it as an email attachment or download it from the internet. There is no loss of information (lossless)

21. AVI AVI = Audio Video Interface Another video format which can be stored Lossy or lossless.