Visual realism is one of the goals of computer graphics. Line drawings, while they can accurately portray an object, lacks in visual realism. The five methods for rendering line drawings more realistic were:

• Orthographic views -- employed in mechanical drawings. Not natural, but conveys information.
• Perspective -- objects further away appear smaller.
• Depth queuing -- adjust intensity based on proximity to viewpoint
• Depth clipping -- adjust front and back (usually) clipping planes
• Visual line determination -- remove edges that are hidden by closer objects, even internal to same object (back edges of a cube)

Photorealism is extremely complex, usually can get close then manually adjust to look right. There are several problems associated with photorealism:

• Perspective
• Shading -- extremely complex
• Shadows -- usually just faked or just the outline is determined
• Visible surface determination -- Object precision versus image precision and efficiency concerns
• Surface details -- texture can affect the others

There are other effects such as transparency, translucency, reflection and refraction to deal with as well.

Visible surface determination using object precision methods basically is done by performing a depth sort. Using back face culling can reduce the number of objects to sort (remember that sorting is at best n log n).

The Depth Sort algorithm is just one of the List Priority algorithms for visible surface determination. Area subdivision was also discussed and rejected for the same reasons.

Image precision methods include polygon, Z-buffer, and ray tracing. The Z-buffer method is the most prevalent method for windowing systems, while ray tracing is used for high-end photorealism applications requiring major computing horsepower.

Detailed notes in pdf format (509 KB)