Rendering a CG Scene - An Introduction to Computer Graphics for Artists - page 218

12.2.6 Render Type Limitations

The impact on lighting of renderer type is quite strong. Here are some of the limitations
of a raster engine:

Dynamic raster only:

• No global illumination/radiosity

• No soft shadows

• No real-time refl ections

• No real-time refractions

• Fill lights of various types can be used to imitate global illumination and radiosity

Dynamic raster plus baked lighting:

• All lighting effects may be processed off-line by a ray tracer and added to texture
or light maps
• Limited to static light solutions. If lights move in the scene, or their values
change, light maps will not be recalculated to match

• Shadow maps may be pre-calculated

Raster rendering then, is more limited than ray tracing, apart from the signifi cant
speed bonus achieved at smaller scene sizes.

12.3 Quality Settings

Quality settings determine the accuracy, type, and number of calculations made for
your render. These are very useful when making test renders, to keep time spent
during iterations to a minimum. For your fi rst renders, you may only need to check
key light color and illumination levels. For that, you don't need anti-aliasing or
shadows, so you can turn them off. Likewise, resolution doesn't have to be high,
texture maps may be turned off, the number of refl ection rays can be zero, and many
other settings may be adjusted to speed up render times and give you the opportu-
nity to make more iterations of your lighting solution.
The highest quality settings can be unrenderable in a reasonable time frame
depending on the complexity of the scene, so your goal as an artist is to fi nd a balance
between practicality and quality. There are many ways to modify your settings and
scene elements to give you exactly what you want within an effi cient render time.

12.4 Render Time

The amount of time it takes a renderer to generate an image is called render time .
The render time for any given frame can vary dramatically, depending on what it
contains. All scene elements affect render time to varying degrees, depending on the