
Models for visual rendering 359
provided by the user. One of the categories will be refined, whereas the other two
will undergo a Gouraud shading or directional shading as per the case. The process
stops when the distance between two successive images becomes less than the threshold
tolerated by the user.
• Several works using perceptual models have also been undertaken in the field of
radiosity. A synopsis of these methods can be seen in (Prikryl & Purgathofer, 1999).
To conclude we can note that several interesting results were obtained in this field.
However, the assessment of vision models, especially the sophisticated ones, remains
expensive,