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1564 Chapter 16: Material Editor, Materials, and Maps
therendererappearinacorrectlinearmanneron
screen.
Ho wever , because the response of photographic
film isn’t linear either, users find that this
theoretically correct value looks too bright and
washed out. A common compromise is to render
to a gamma of 1.8, making things look more
photographic; that is, as if the image had been shot
on photographic film and then developed.
Tone mapping
Another method for mapping the physical
energies inside the renderer to visually pleasing
pixelvaluesisknownastone mapping.This
can be accomplished either by rendering to a
floating-point file format and using external
software, or with a plug-in that al lows the renderer
to do it on the fly. In 3ds Max such plug-ins are
knownasexposurecontrolsandareaccessedfrom
the Environment dialog.
Note: When using the Logarithmic Exposure
Control, the need for gamma correction is largely
replaced. You should use either gamma correction
or the Logarithmic Exposure Control but not both.
Use Final Gathering and Global
Illumination
The Arch & D esign material is desig ned to be
used in a realistic lighting environment; one that
incorporates full direct and indirect il lumination.
mental ray provides two basic m ethods for
generating indirect light: Final Gathering and
Global Il lumination. For best results, b e sure to
use at least one of these methods.
At the very least, enable Final Gathering, or
use Final Gatheri ng combined with Global
Illumination (photons) for quality results.
P erformance tips for using Final Gather and
Global Illumination can be found here (page
2–1569).
If you use an environment for your reflections,
makesurethesameenvironment(orablurred
copy of it) is used to light the scene through Final
Gathering. In 3ds Max this means you should
include a Skylight (page 2–1296) in your scene set
to U se Scene Environment, or use Daylight system
(page 1–418) with Skylight set to mr Sky.
Use physi cal ly cor r ect li ghts
Traditional computer-graphics light sources live
in a cartoon universe where the intensity of the
light doesn’t change with the distance. The real
world doesn’t agree with that simplification. Light
decays when leav ing a light source due to the fact
that l i ght r ays diverge from their source and the
intensity of the lig ht changes over distance. This
decay of a point light source is 1/d
2
;inotherwords,
light intensity is proportional to the inverse of the
square of the distance to the source.
One of the reasons for this traditional
oversimplification is the fact that in the early days
of computer graphics, tone mapping was not used
andproblemsofcolorsblowingouttowhitein
themostundesirablewayswasrampant. (Raw
clipping in sRGB color space is displeasing to the
eye, especially if one color channel clips earlier
than the others. Tone mapping generally solves
this by “sof t clipping” in a more suitable color
space than sRGB.)
However, as long as only Final Gathering (FG)
is used as indirec t illumination method, such
traditional simplifications still work. Even light
sources with no decay stil l create reasonable
renderings. This is because FG is concerned only
w ith the transport of light from one surface to t he
next, not with the transport of light from the light
source to the surface.
It’s when working with Global Illumination (GI)
(that is, with photons) the troubles arise.
When GI is enabled, light sources shoot photons.
For the Arch & Desig n m aterial (or any other