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

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.

Review: Storing images as pixels

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.

What do different colour depths look like?

1 bit (2 colour)4 bit (16 colours)8 bit (256 colours)24 bit (16 M colours)

Each pixel is stored in three bytes.

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

Choosing colours…

http://html-color-codes.info/

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.

Lossy Compression

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.

Animated image files

Image format wars!

Image file formatsGIFGraphics Interchange File

JPEGJointPhotographExpertsGroup

PNGPortableNetworkGraphics

BMPBitMap

Lossey No Yes No No

Can animate Yes No No No

Transparency?

Yes No Yes No

Comments Low 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.

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

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.

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.

Zip

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)

AVI

AVI = Audio Video Interface

Another video format which can be stored Lossy or lossless.