File Formats File Formats In this lesson we

File Formats

File Formats In this lesson, we will be looking at: • The two main families of computer graphics – vector and bitmap • Different types of bitmap files, and which is best to use • Other types of file formats – e. g. sound, text and data • Why it’s important to choose the right format for your file

Bitmap Graphics When you save bitmap graphics, the information that makes up the picture is saved as a grid. This is like drawing a picture by shading in the squares on a piece of graph paper (only the squares are so small that often you can't see them). The quality of the picture is affected by the size of the squares, and how many there are.

Disadvantages • If you increase the size a picture, it is still made up of the same number of squares, but the squares get bigger. • It is difficult to edit a picture once you've entered it – you can’t layer objects. • Information is saved for every square (pixel), even if you haven't drawn anything in it. This means that the files you create are always big.

Uses of Bitmaps images are created by: • Paint/Paintbrush • Photo. Editor • Photo. Shop • Paint Shop Pro And are used in: • Web pages • CD-ROMs, etc.

Vector Graphics When you create vector graphics, the file stores the information needed to recreate the shapes, for example thickness or angle of the lines, or the radius of a circle. This means that the quality of your drawing is not affected by its size. Also, each “object” you draw is stored separately, so that you can move them around, or take one from the back and bring it to the front.

Advantages • The quality stays the same when you increase the size. • Only information about the “objects” you draw is stored in the file – this means that the files tend to be much smaller. • Each “object” you draw is stored separately, which means that the picture is easier to edit, and foreground and background parts can be swapped around.

Uses Vector graphics are used in: • Clip. Art and Office Drawing tools • Corel. Draw • The Ilinc Whiteboard / Powerboard The disadvantage is that there are some things you can’t do, such as • flood filling • spraying

Bitmap Files Various common picture formats use bitmaps: • (Windows) bitmap -. bmp • Graphics Interchange Format -. GIF • Joint Photographic Expert Group -. jpg Each supports a different range of features: • Colour depth • Compression • Transparency

Colour Depth • Different formats support different numbers of colours. • GIFs can only have 256 different colours in them, which makes them more suitable for simple pictures and diagrams • Jpegs can contain up to 16 million different colours, which makes them more suitable for photographs and other images with shading.

Transparency Some formats (e. g. GIF) allow you to make one colour or area of the image transparent, so that you can see the background through it.

Compression Different formats use different compression techniques to make the file smaller: GIF (3 k) "high quality". jpeg (7 k) "low quality". jpeg (2 k)

Sound Files There are two families of sound files that are analogous to bitmap and vector graphics: • Wave files – such as. wav, . wma and mp 3. These are recordings of the actual sounds. wavs are uncompressed, and. wma and MP 3 use lossy compression • MIDI files – like vector graphics, these contain instructions on which notes to play - a bit like the paper rolls in a pianola, or the discs/cylinders in a music box – and your soundcard makes the sounds

Other File Formats Text can be saved in the following portable formats: • plain /ASCII text -. txt • Rich Text Format -. rtf • the new Open Document format -. odt The most common portable format for data (which can be opened in Excel or Access) is: • Comma-separated variables -. csv

Why Does It Matter? • If you are sending the files to other people (or putting them on a web-site) it is a good idea to use a portable format so that everyone can open them • If you are using the internet, or another network, to transfer the files, then it’s a good idea to make your files smaller so that they are quicker to download. • You can make files smaller by choosing a more efficient format or by using compression.