2012

Table Of Contents
Soft Shadows
Presenter includes shadows generated from pre-calculated, shadow maps
for each shadow-casting light source. The use of shadow maps enables rapid
rendering of shadows with soft or graduated edges. The shadow resolution
can be controlled to balance performance and image quality.
Soft shadows are only suitable for use with small models, and are disabled by
default. For large models, the generation of the shadow maps can use excessive
amounts of time and memory. Soft shadows generated for large models are
often too vague and dispersed without using an excessively high resolution,
which uses even more memory and time.
Physically Accurate Lights
By default, Presenter uses lights with unitless, or empirical intensities. These
are physically meaningless, and are just chosen to give a visually pleasing
result. Presenter can also use physically accurate intensities. These are defined
in real-world units such as Candela, Lumen, or Lux. However, once you start
using lights with real-world intensities, you start to produce images with a
real-world variation in luminance values.
By default, Presenter uses lights whose intensity remains constant as you
move further from the light. In the real-world intensity is reduced proportional
to the inverse square of the distance from the light. Changing a lights Fall
Off parameter to Inverse Square Law will more accurately model a lights
fall off in intensity. However, once you start using lights with real-world fall
off, you start to produce images with a real-world variation in luminance
values.
In the real world, the human eye is capable of resolving images in extremely
varied lighting conditions, ranging from bright sunshine reflecting off snow
to a room lit only by a single candle. In computer graphics, however, you
need to produce an image on a display device which has a very limited range
of luminance values. Therefore, it is necessary to compress the range of
luminance values found in a real-world scene into the displayable range in
such a way as to produce a realistic looking image.
Photography, of course, has exactly the same problem. If a photographer (or
camera) does not take into account the light levels in a scene before calculating
the exposure of the shot, the likely result will be an image which is either
over-exposed (everything is too bright) or under-exposed (everything is too
dark). A professional photographer will also use different speeds of film for
574 | Chapter 13 Create Photorealistic Visualizations