When surfing the Web, you will have noticed web sites where the images load very slowly whereas other images don't match with the theme of the site or appear blurry. Presenting a professional image for your business means your web site design must beprofessional also.

Part 1of this article discussed when to use images for your web site and what image file formats to use on the Web. In this article (Part 2), we will discuss how to optimize your images for the Web.

Image optimization is the art of making your images suitable for the Web. There is a large difference in preparing your graphics for print compared to the Web. In print you have to have as much data as possible to get a good graphic. The main factors that influence the display of graphics for the Web, are the size of the file and the screen display quality of the graphic.

Factors Affecting Web Graphics

1. File Size

   When you design web pages you need to create a balance between visual appeal and page download time. If your page has too many images on it, it will take too long too load and visitors will not stay around to wait.

2. Cropping

   This means cutting out unwanted areas of your image. It decreases the file size and helps visitors to focus on your image.

3. Anti-aliasing

   Jagged edges of an image can be prevented by anti-aliasing. This creates a blended edge around an image. Because of the extra colors necessary to create the blend, file sizes of anti-aliased GIFs are a little larger. Use anti-aliased graphics in almost all cases, except when creating very small type as graphics.

4. Bit Depth and Screen Resolution

   Bit depth refers to the number of colors in an image or the number of colors a computer system is capable of displaying. To calculate bit depth, one bit equals 2 colors, then multiply 2 times 2 to arrive at each higher bit depth. Quality and file size decrease as bit-depth decreases.

   New computers support thousands or millions of colors (32-bit), but many older color systems can only show up to 256 (8-bit) colors at a time. This reality imposes limits on the size of files and number of colors that can be included in Web graphics.

   Check how your image appears with a 256-color monitor and a true-color monitor. Do this on your PC using the Setting/Control Panel/Display option, then select the Settings tab/256 color option.

5. Image Resolution

   Monitors typically display data at 72 dpi (dots per inch). Therefore, always save your files on the Web at 72 dpi. Always resize your image in your graphics software before you insert it onto your web page. If you resize its dimensions when it's already on your site, it will look distorted.

6. Browsers

   Someone viewing your site is subject to a completely different result depending on which browser he is using. Your images may appear harmonious in Internet Explorer (IE) but may be broken up in Netscape Navigator (NN). Therefore check your image for differences with Internet Explorer (IE) and Netscape Navigator (NN) browsers. Your images should appeal to all users.

   Unfortunately AOL has its own browser, which filters sites through its own AOL proxy system. This means all graphics are converted from JPEG and GIF to the ART format.

   Most AOL users also use their browsers with the default "compressed graphics" checked, so what normally looks good in IE or NN, will look blurry or distorted on AOL. To change this, AOL users need to go to preferences and check "never compress graphics".

7. Caching

   This is a temporary storage area of your hard drive where browsers keep files while they display them. You can create a consistent look and feel to your Web Site, by reusing another graphic on another page. You will be retrieving it from the cache. The more graphics that you reuse, the faster your pages will load.

Testing

To test load times of your pages you need to first publish them and then clear the cache in your computer before loading them, and timing them, from the Internet. Put the url in your browser address box, start timing when you hit Go and stop when the word 'Done' appears in your status bar.

Images are the main factor that contributes to slow loading of your web pages. By implementing these techniques for optimizing your images, visitors will have a far more pleasing experience.

Part 3 of this article will discuss other methods for creating fast loading images when creating a professional web site.

Copyright 2002 Herman Drost