POV-Ray : Documentation : Radiosity with conventional lighting
  POV-Ray 3.6 Documentation Online View Introduction Radiosity without conventional lighting Radiosity with conventional lighting

The pictures here introduce combined conventional/radiosity lighting. Later on you can also find examples for pure radiosity illumination.

The following settings are default, the result will be the same with an empty radiosity block:

  global_settings {
    radiosity {
      pretrace_start 0.08
      pretrace_end   0.04
      count 35

      nearest_count 5
      error_bound 1.8
      recursion_limit 3

      low_error_factor 0.5
      gray_threshold 0.0
      minimum_reuse 0.015
      brightness 1

      adc_bailout 0.01/2

The following pictures are rendered with default settings and are made to introduce the sample scene.

All objects except the sky have an ambient finish of 0.

The ambient 1 finish of the blue sky makes it functioning as some kind of diffuse light source. This leads to a bluish touch of the whole scene in the radiosity version.
no radiosity radiosity (default settings) difference w/o radiosity

You can see that radiosity much affects the shadowed parts when applied combined with conventional lighting.

Changing brightness changes the intensity of radiosity effects. brightness 0 would be the same as without radiosity. brightness 1 should work correctly in most cases, if effects are too strong you can reduce this. Larger values lead to quite strange results in most cases.
brightness 0.5 brightness 1.0 brightness 2.0

Changing the recursion_limit value leads to the following results, second line are difference to default (recursion_limit 3):
recursion_limit 1 recursion_limit 2 recursion_limit 5
recursion_limit 1 (difference) recursion_limit 2 (difference) recursion_limit 5 (difference)

You can see that higher values than the default of 3 do not lead to much better results in such a quite simple scene. In most cases values of 1 or 2 are sufficient.

The error_bound value mainly affects the structures of the shadows. Values larger than the default of 1.8 do not have much effects, they make the shadows even flatter. Extremely low values can lead to very good results, but the rendering time can become very long. For the following samples recursion_limit 1 is used.
error_bound 0.01 error_bound 0.5 error_bound 1.0
error_bound 0.01 (difference) error_bound 0.5 (difference) error_bound 1.0 (difference)

Somewhat related to error_bound is low_error_factor. It reduces error_bound during the last pretrace step. Changing this can be useful to eliminate artefacts.
low_error_factor 0.01 low_error_factor 0.5 low_error_factor 1.0
low_error_factor 0.01 (difference)   low_error_factor 1.0 (difference)

The next samples use recursion_limit 1 and error_bound 0.2. These 3 pictures illustrate the effect of count. It is a general quality and accuracy parameter leading to higher quality and slower rendering at higher values.
count 2 count 35 (default) count 300

Another parameter that affects quality is nearest_count. You can use values from 1 to 20, default is 5:
nearest_count 1 nearest_count 5 nearest_count 10

Again higher values lead to less artefacts and smoother appearance but slower rendering.

minimum_reuse influences whether previous radiosity samples are reused during calculation. It also affects quality and smoothness.
minimum_reuse 0.2 minimum_reuse 0.015 minimum_reuse 0.005
minimum_reuse 0.2 (difference)   minimum_reuse 0.005 (difference)

Another important value is pretrace_end. It specifies how many pretrace steps are calculated and thereby strongly influences the speed. Usually lower values lead to better quality, but it is important to keep this in good relation to error_bound.
pretrace_end 0.2 pretrace_end 0.04 pretrace_end 0.002

Strongly related to pretrace_end is always_sample. Normally even in the final trace additional radiosity samples are taken. You can avoid this by adding always_sample off. That is especially useful if you load previously calculated radiosity data with load_file.
always_sample on always_sample off always_sample off (difference)

The effect of max_sample is similar to brightness. It does not reduce the radiosity effect in general but weakens samples with brightness above the specified value.
max_sample 0.5 max_sample 0.8 default

You can strongly affect things with the objects' finishes. In fact that is the most important thing about radiosity. Normal objects should have ambient finish 0 which is not default in POV-Ray and therefore needs to be specified. Objects with ambient > 0 actually emit light.

Default finish values used until now are diffuse 0.65 ambient 0.
diffuse 0.65 ambient 0.2 diffuse 0.4 ambient 0 diffuse 1.0 ambient 0

Finally you can vary the sky in outdoor radiosity scenes. In all these examples it is implemented with a sphere object. finish { ambient 1 diffuse 0 } was used until now. The following pictures show some variations:
ambient 0 diffuse 1 ambient 0 diffuse 0 (no sky) yellow-blue gradient

More about "finishes" Introduction Radiosity without conventional lighting

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