Worksheets, posters, newsletters, whiteboard presentations, wallcharts - all teachers make them and most include graphics of some kind, be they drawings, cartoons, graphs or charts. Sometimes they look good, sometimes they don’t. Sometimes they take an age to load and sometimes they’re quick.

You can spend a lot of money on graphics software, but free, open-source applications are more than adequate for school use. One way to create computer images is to use bitmap graphics, consisting of dots of colour (pixels). For bitmap work, Gimp (www.gimp.org) has a silly name (from Gnu Image Manipulation Program) but is a good package for editing graphics and logos, and is almost as powerful as Photoshop.

Like any complex piece of software, it takes practice to get the best from it, but the help system is good and there are thousands of decent tutorials on the web. The Gimp interface looks strange at first - when you run the program it simply loads the toolbox - go to File > Open though, and the image you are working on opens in its own window. Gimp has an “intelligent cursor” so just move the mouse slowly over the icons and read the pop-ups.

So what happens when it’s time to print out your wonderful artwork? You don’t want it blocky like the look of some school posters. Images viewed on-screen generally have 72 dots per inch (dpi) but a printed image has a larger resolution - 300dpi. A 72dpi image printed out will be very small, or if stretched in size will look blocky. Most graphics applications allow you to increase the pixel count by inserting extra pixels. This is fine as long as you don’t overdo it.

A lot of pixels means a large file size, which could be a problem. File size can be reduced by defining patches of colour rather than every dot, or by limiting the range of colours used. Jpeg images use the former method: it’s effective but can lead to over-simplified images. Files ending in.png (ping) gives better results.

“Indexed colour” reduces the palette, using a few hundred colours instead of millions. This cuts the file size dramatically. It is used by web designers to make pages load faster and is useful on virtual learning environments and whiteboards. Such images are usually saved in.tif or.gif formats.

For more elaborate worksheets and posters, you need a desktop publishing (DTP) program, such as Scribus (www.scribus.net), which is also free. The basic concept of DTP is that you create “frames” into which you can place text, images or tables. Text frames can be moved and linked so text flows across columns or pages, images can be moved and resized, text forced to flow round images and so on; people have published complex books using Scribus. Once again, the intelligent cursor and Help will guide you through. For more information, click the ScribusWiki link on the main page.

It takes years to become a graphic designer, so don’t expect miracles immediately. But with a little bit of time and effort, you can produce graphics that won’t embarrass you in front of your pupils.

Phil Thane is a freelance writer, part-time teacher and ICT specialist.