Not Just Decoration: Quality Graphics for the Web

Introduction

The means of providing and using high quality textual information on the Web has received a great deal of attention. Of course, there is still plenty of low-grade textual information out there. But the requirements are well understood and the infrastructure is in place for those who wish to generate or use quality text.

Much graphical material on the Web is also of poor quality, but in contrast the requirements for high quality graphics on the Web have received much less attention. Granted, many graphics are mere adornment, but some are not. Graphics can be valid information in their own right.

It would also be dangerous and limiting to assume that browsing constitutes the totality of present and future Web use. In some applications, the graphical component can be essential. Thus, it makes sense to evaluate the particular requirements for quality Web graphics.

Application areas

A sample of existing and potential application areas dependent on high quality images:

• Inline graphics were first added to the web because they were needed for a distributed, collaborative scientific visualisation application. Thus, NCSA Mosaic [1] was born. Scientific visualisation remains an application where high quality graphics are an essential requirement and where graphics constitute the bulk of the information.
• Commercial applications such as product design and collaborative evaluation of prototypes clearly benefit from using the Web, and also require a high level of colour fidelity in rendition of images.
• In the medical and veterinary fields, clear and portable images are essential if clinical decisions are to be made using them; there is also the need for tightly coupled image metadata for safety and liability reasons.
• Accurate, repeatable device independent colour representation is an emerging key requirement in advertising. Extreme care is currently taken with printed materials to ensure consistent colours for such things as brand identification and corporate identity, but the infrastructure is only slowly being put in place to assure a similar level of fidelity on the Web.
• Last but not least, computer graphics research has a clear need for the dissemination of accurate images for viewing and analysis by colleagues worldwide.

Scope

This paper will survey some major areas affecting 2 dimensional, static, raster graphics quality. Vector graphics (such as CGM), 3 dimensional graphics (such as VRML), animations and movies are not considered.

It will focus on areas such as accurate colour and tonal rendition which may as yet be unfamiliar to developers of Web user agents. Topics which are important for Web graphics in general, but do not strictly relate to graphics quality - such as compression efficiency - are also outside the scope of this paper.

Effect on Web user agents

Computer Graphics can be seen as a somewhat specialised area - particularly where accurate rendition is required. Yet parts of it need to be understood to produce good graphics. Experience has shown that users can be harshly critical of browsers with poor image quality, even if these same browsers excel in other areas. The thrust of this paper is to pull together separate strands of computer graphics as they relate to Web user agents, to make it easier to provide the increasingly high levels of graphical quality that users are demanding.

A number of different quality requirements are discussed in this paper. Attempting to implement a single one of these in isolation can be difficult, as there are strong interactions between them. Partial implementation still requires an awareness of the other factors. This paper highlights known interdependencies to make the implementors job easier and prevent nasty surprises.