Rendering
times are proportional to the resolution of the image. An
image with a resolution of 1000 by 1000 pixels will take approximately
4 times as long to render as one with a resolution of 500 by 500 pixels.
To reduce the time taken for each iteration sub-images may be used to
limit the size of the area rendered.
The
time taken to render an image is affected by the rendering mode. The flat rendering mode is the fastest, followed
in order by Gouraud, Phong, Scanline preview, Scanline full, Raytrace
preview and Raytrace full. The ray-tracing rendering modes are not normally
required. Raytrace full may be used instead of Scanline full when shader
aliasing occurs. The ray-tracing rendering modes use the ray-tracing technique
to calculate surface visibility and are consequently slower than the scan-line
based rendering modes. The reflection and refraction effects of ray-tracing
are available in the Scanline preview and full rendering modes, combining
the speed of scan-line visibility with the visual effects of ray-tracing.
Rendering
time will increase with the number of lights.
Normally, most scenes require only two or three lights. The relative computation
time required for each light type, in increasing order, is as follows:
ambient, eye, distant, point and spot. Shadows from lights will increase
the rendering time. Shadows are both computationally and memory intensive.
Shadows from point lights are especially memory intensive. Turn shadows
off during the iteration process. The normal resolution for shadows should
be in the range of half the image resolution and the full image resolution.
Rendering
times can be reduced and the quality of shadows increased if objects that
do not cast shadows onto other objects are excluded when a shadow is created
for a light. For example, if an
image is being created of a widget on a flat surface, then the flat surface
will not cast shadows onto any other object and can therefore be excluded
from the shadow creation process.
The
number of materials used in a scene does not affect rendering time.
The
types of materials used in a scene may affect rendering time. In fact, some materials are slower than others.
Any materials that use ray-tracing reflectance shaders, like conductor,
mirror, dielectric or glass, will be slower than the simpler reflectance
shaders like matte, plastic, Phong and metal. Using the displacement shaders
like rough and cast will increase rendering times. The image area covered
by objects using the 'slower' materials will affect the rendering time.
If an object is quite small in the image then attaching a 'slower' material
to it will have a small effect on the rendering time. However if the object
covers a large area of the image, then the effect on the rendering time
will be greater.
Rendering
time is affected by the complexity of the geometry being rendered. Sub-images and selecting sub-sets of the geometry
may be used to reduce the rendering time during the iteration process.
Using
displacement shaders increases rendering times.
Rough and cast are especially computationally intensive.
Plain
colored color source shaders like plain are quicker than the more complex
ones like simple wood and marble.
The plain and graduated backgrounds are quicker than the clouds background.