18.104.22.168 Radiosity without conventional lighting
You can also leave out all light sources and have pure radiosity lighting. The situation then is similar to a
cloudy day outside, when the light comes from no specific direction but from the whole sky.
The following 2 pictures show what changes with the scene used in part 1, when the light source is removed.
(default radiosity, but
recursion_limit 1 and
You can see that when the light source is removed the whole picture becomes very blue, because the scene is
illuminated by a blue sky, while on a cloudy day, the color of the sky should be somewhere between grey and white.
The following pictures show the sample scene used in this part with different settings for
(everything else default settings).
This looks much worse than in the first part, because the default settings are mainly selected for use with
conventional light sources.
The next three pictures show the effect of
recursion_limit is 1 here)
Without light sources, this is even more important than with, good values much depend on the scenery and the other
settings, lower values do not necessarily lead to better results.
If there are artefacts it often helps to increase
count, it does affect quality in general and often
helps removing them (the following three pictures use
The next sequence shows the effect of
nearest_count, the difference is not very strong, but larger
values always lead to better results (maximum is 20). From now on all the pictures use
minimum_reuse is a geometric value related to the size of the render in pixel and affects whether
previous radiosity calculations are reused at a new point. Lower values lead to more often and therefore more accurate
In most cases it is not necessary to change the
low_error_factor. This factor reduces the error_bound
value during the final pretrace step.
pretrace_end was lowered to
0.01 in these pictures,
the second line shows the difference to default. Changing this value can sometimes help to remove persistent
gray_threshold reduces the color in the radiosity calculations. as mentioned above the blue sky
affects the color of the whole scene when radiosity is calculated. To reduce this coloring effect without affecting
radiosity in general you can increase
gray_threshold. 1.0 means no color in radiosity at all.
Another important parameter is
pretrace_end. Together with pretrace_start it specifies the pretrace
steps that are done. Lower values lead to more pretrace steps and more accurate results but also to significantly
It is worth experimenting with the things affecting radiosity to get some feeling for how things work. The next 3
images show some more experiments.
Finally you can strongly change the appearance of the whole scene with the sky's texture. The following pictures
give some example.
Really good results much depend on the single situation and how the scene is meant to look. Here is some
"higher quality" render of this particular scene, but requirements can be much different in other