Rendering and Compositing - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 233

been reflected or refracted by glossy surfaces that
then contribute to diffuse illumination. Examples
include the bright patterns of sunlight in a swim-
ming pool and light focused by a magnifying glass
onto a surface.

Rendering with Cycles
Many of the Render tab options remain the same
in Cycles, so I will just cover the important differ-
ences here.

Sampling
The Sampling panel determines how many samples
to calculate for each pixel in the image, which is the
main way Cycles determines the quality and noisi-
ness of your final image. The Render and Preview
options determine how many samples to render for
each pixel in an image before terminating the ren-
der. (Use Render for proper renders and Preview for
the Cycles preview in the 3D Viewport.) More passes
will result in less noise, but the number of passes
required to get a noise-free image will vary widely
according to the contents of your scene. Seed sets
a random value for Cycles to use for sampling, and
different seeds will produce different noise patterns.
You can use the Clamp option to prevent fireflies, ,
which are overly bright pixels caused by noise from
bright lights or specular highlights. To do so, set
the maximum brightness (the clamp value) for a
sample to a nonzero number (a value of around 3
works well). This keeps overly bright samples from
throwing off the average value of a pixel too much,
though it comes at the cost of some accuracy in
rendering. (If you leave this at the default of 0, this
feature will not be used.)

Film
You can use the Film panel's Exposure setting
to change the exposure of your render to either
brighten or darken scenes overall. (However, it's
best to change the settings on your lamps instead
for finer control.) The Transparency checkbox deter-
mines whether your background renders as trans-
parent or uses your global settings. The drop-down
menu on the right sets the pixel filter type (with the
width of the filter below it). Smaller widths produce
sharper-looking edges but can cause aliasing. Larger
widths give smoother renders at the expense of a
small amount of blurring.

Layers
Cycles works much the same as Blender Internal
when it comes to layers, but it supplies a different
range of passes. Cycles will split up each kind of
light ray (diffuse, glossy, and transmission) into
separate passes and can split up those passes further
into direct and indirect passes. These features can
be useful when compositing.

Balancing Render Time and Quality
When rendering any CG scene, the aim is to get
the nicest render possible in the shortest amount of
time. This can be tricky given the number of vari-
ables you can change, all of which affect how long
an image will take to render. Still, there are some
general principles.

Light Paths
The Light Paths panel supplements the options in
the Samples panel, allowing you to go deeper into
how Cycles renders your scene. Specifically the
Light Paths panel lets you determine what types of
rays to render and how many bounces to calculate
before terminating a ray. More bounces give more
accurate (and slightly brighter) renders, at the cost
of extra render time.
The Transparency, Light Paths, and Bounce set-
tings define the maximum number of light bounces
that Cycles will calculate for each type of interaction
with light. The Max setting sets the overall maxi-
mum number of bounces, while the other settings
restrict specific types of rays to fewer bounces. The
Min setting for Transparency and Overall Bounces
enables early termination of refracted rays, resulting
in faster rendering with the loss of some accuracy.
The No Caustics and Shadows options let you
turn on and off caustics and ray-traced shadows
to speed up rendering. Caustics are rays that have

Start simple and be organized. Organize your
objects onto layers to make it easier to render
different aspects of the scene. Also, make sure
you don't have any unneeded objects in your
scene on visible layers when rendering.

Experiment. If your renders are slow, try changing
one setting at a time to see what most affects
your render times. For example, change a ren-
der setting or the number of samples on a lamp.
Or enable or disable some aspect of a mate-
rial, such as subsurface scattering or ray-traced
reflections. Changing one thing at a time will let
you see exactly what makes the most difference,