8 Rendering

I. Rendering & the Design Process

Photographic analogy: Lights, Camera, Action!
Artificial Stage sets rather than accurate portrayals

1. Create the Model
2. Find Camera views
3. Set up Lighting, test
4. Assign Materials & background
5. Map textures
6. Choose Rendering Mode: Quality vs. Time
7. Render, save to file
8. DESIGN: Revise model, lighting, materials
9. Re-render
10. Post-process with image processing

 Troubleshooting Renderings

• Set Image Size
• Adjust Rendering Quality Mode (Full Z-Buffer)
• Thumbnail: test render with layers off
• Step by step to learn factors, take notes on variables
• Check reference images in Radiozity manual
• Other solutions

II. Light

A. Light rays hitting our eyes allow us to see objects reflecting or radiating light.

Shade: non-lit surface

Shadows: Projected darkness

Examples from Lachmi Khemlani's book:

• Opaque vs. Transparent
• Darkness
• Hard vs. Soft
• Level of Detail
• Shadows on (in Lights, Display Options, Rendering Attributes)

B. Types of Light sources

• Directional = parallel rays, sun settings
• Point source = all directions
   Intensity by inverse square law
• Spot = adjustable cone
• Ambient = flat general background illumination (non-directional)
• Projector lights
• Area lights

C. Using Lighting

• Direction
• Contrast
• Color
• Key and Fill Lights
• Combining sources
• Light, Shadow & Feelings

D. Rendering Settings

• Raytracing vs. Radiosity
• "Renderzone" vs. "Raydiozity"
• Illumination Analysis

IV. Perception and Point of View

From the geometry of a 3D model we can extract all the traditional architectural projections.
Each 2D view reveals and conceals: distortion of angle, dimension or visual relationship must occur.

A. Parallel projections:

• Orthographic (elevations & sections) maintain angle and dimension only in planes parallel to the projection plane.

  Foreshortening occurs on all tilted planes.

• Axonometric drawing maintains parallel lines along axes. Measurements may either be true or compressed along these axes.
• Isometric drawings, a special case of axonometric, hold the x-y-z axes at 120 degrees apart.

B. Oblique projections hold either the elevation or the plan constant while lines in depth are taken at an angle. Projection lines are parallel but not perpendicular to the picture plane.

C. Perspective projections are created by projection rays from the subject converging to the viewers' eye.
Converging diagonals provide a focus for the picture

• 1 point perspectives have a frontal formality created from balanced, bi-laterally symmetric rays.
• 2 point perspectives can be much more dynamic if one set of converging lines dominate.
• 3 point perspectives approximate the fisheye distortion which our eyes see.

D. Eye height determines the viewer's relationship to the subject.

• The viewer is dwarfed by monumental architecture is seen from a low vantage point.
• Conversely, a god's omniscient view is conveyed by a high vantage point.
• The contrast of large foreground elements can diminish a receding background and accentuate a dominant viewpoint.

E. Depth of field (inverse to the size of the cone of vision) determines

• the amount of information which is compressed into the picture
• the amount of angular and dimensional distortion

As the depth of field goes to infinity, the projection rays become closer to parallel and the picture goes towards an orthogonal or axonometric projection.

F. Slight changes in eyepoint, target point, depth of field and cropping can completely alter the composition of a picture.

Cropping focuses the viewers attention. Tight cropping provides the viewer with little context. (Sheeler & Piranesi use tight cropping to exaggerate the dynamic tension of juxtaposed geometry).

III. Materials

A. Material attributes = Surface qualities

• Surface color (local color)
• Reflectivity (Shininess)
• Transparency
• Bump

B. Texture mapping

• Image maps
• Tiled copies vs. single copy (Full-face)
• Mapping parameters

C. Alpha Channel: greyscale or black and white stencil

• Bump mapping
• Transparency mapping

D. Decals w/ backgrounds (Centered Texture)

IV. References

3D Animation Workshop by Rob Polevoi (see lessons 17-21 on rendering & lessons 54/55 on texture mapping)