Images

The use of images is one of the features that make the World-Wide-Web so attractive to many users. However there are a number of points that the HTML author should be aware of before using images extensively.

• Image size

  If you include an in-line image (i.e. one that is displayed as part of the page) then the binary version of the image has to be transferred. Even a small image can be 5-10 kBytes which is the size of a fairly large text page. The incorporation of such an image will double the down-load time.

  Images obtained by scanning photogrpahs and other art-work are normally much larger then those generated by paint programs.

  Many users particularly on slower lines will turn off the downloading of images meaning that they won't see the picture. Remember this before designing pages that depend heavily on visuals.

• Repeated use of images

  If you include the same image several times, if every reference to the image uses the same URL then the image will only be transferred once. Nearly all browsers will maintain a cache of local copies and spot that the image is already in the local image cache.

• Text only browsers

  Some older and less powerful computers use text only browsers, of which Lynx is the best known. Text only browsers are also used by the visually handicapped. Consider such people when designing your pages.

• Off-line images

  In-line images are associated with the <img> tag. A simple link to an image such as

     Here is a <a href="bigpicture.gif"> picture of the cat</a>
  

  will only cause the image to be downloaded if the user selects the link. If you want to present images this way it is very good and courteous to users to indicate the size of the image. For example

     Here is a <a href="bigpicture.gif"> picture of the cat</a>(247 kByte)
  

  The user can then decide whether they want to use up the connect time (and 'phone bill) to download the image.