The Motive Web Design Glossary
optimise/optimize, optimisation/optimization
The aim of optimisation is to reduce the time it takes to access a website (or run a program). Images, application and (X)HTML code can all be optimised.
Image optimisation
For imagery, optimisation involves choosing a suitable graphic compression format. Compression reduces the image filesize and consequently the time it takes to download and display in a browser. Common compression types include GIF, JPEG and PNG. Many compression formats reduce filesize by removing information from the image (downsampling). For example, the JPEG format reduces overall tonal range to reduce filesize—reducing the tonal range means that highlights and shadows become less pronounced.
Reducing the number, and filesize of the images can be a significant issue for websites with large subscriber bases such as news sites. Site owners are charged for the amount of information (data) downloaded from their sites (traffic). The more popular the site and larger the images the greater the traffic costs.
(X)HTML optimisation
Using CSS significantly improves the speed of a website—a single stylesheet can be used for all pages but is downloaded only once.
The time it takes for a webpage to display is affected by a number of factors:
- the number (and filesize) of images used in the webpage
- the structure of the underlying XHTML code, for example; setting height and width attributes enables the browser to reserve the correct amount of space for an image (before it has downloaded) avoiding the browser redrawing the webpage
- the browser’s rendering engine (how the program used to access the web loads each webpage)
- browser caching: if the webpage, images, stylesheets, etc. are stored locally they do not need to be downloaded
- the user’s connection speed (i.e. dial-up modem will take longer to download a webpage than a cable modem)
- the speed of the server hosting the website
- Internet traffic
Search engine optimisation
Webpages can also be optimised for to improve ranking on search results pages (search engine optimisation).
download/upload, GIF, JPEG, PNG
References and further reading
- Average webpage size triples since 2003 (Websiteoptimization.com)
28 Apr 2008: Statistical analysis of webpage filesize, increase in webpage filesize and media types (video, images, Javascript, CSS, etc.). - Page Speed Online (Google)
Enter a webpage address for handy optimisation tips. - Web Page Analyzer (Websiteoptimization.com)
Enter a webpage address to generate a ‘Webpage speed report’ with recommendations on how to improve page performance.
Glossary A-Z