section 4: using images

Now that you have learnt almost everything this is to know about text and text formatting, it's time to move on to other forms of media, in particular graphical images. Images can be used in two ways on a web page. First they can be used for decorating web pages, which is one of the most important reasons for the success of the internet. Images allow people to really visualise what the text is saying plus they provide a way to produce visually pleasing web pages.

Secondly, images can be combined with the ANCHOR tag or in IMAGE MAPS, so that when users click on the image it takes them to a link.

Image formats

On the internet there are two main image formats...

• JPEG images, files end in .jpg or jpeg.
• GIF images, files end in .gif.

The main difference between the two formats is that GIF images are best for simple images that contain mostly simple computer generated elements (such as rectangles, circles). For more complex images such as pictures scanned in by a scanner or more complex computer generated images (such as circles with gradient fills etc.) are best saved with the JPEG format. JPEG images have one major advantages over GIF images, you can balance out the size of an image by compromising the quality. Most picture processing programs allows users to save in JPEG format and also to choose the image compression ratio, a larger ratio means a smaller image file but the quality of the image will be reduced. The main advantage of the GIF format allows you to create simple animations on your web pages but to do this you need an externel drawing package that will create the animation, no specific information about creating GIF animation is given in this tutorial but if you see an interesting animation on the internet that has not been copyrighted by anyone (Copyright being an extremely complex issue on the Internet since to view an image your the reader needs a copy of the image on their computer) then you can use it in your own pages simply by saving the GIF file.

I say that the ability to compress images by comprimising quality is important because it has been shown that an internet user will wait up to 15 seconds for an internet site to load up. If it takes longer then this, they are like to just go to another site. For this reason you should try to keep the total space taken up by images a maximum of around 45kBs (kilobytes), that may mean reducing the quality of some images to do this. You done have to stick to this rule but you can make real decisions about the quality and the download time of your site.