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<strong class="NavBar">POV-Ray 3.6 for UNIX documentation</strong><br> <strong>2.3.7
Radiosity</strong>
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<h3><a name="s02_03_07">2.3.7 </a>Radiosity</h3>
<a name="s02_03_07_i1"><a name="Radiosity, tutorial"></a>
<h4><a name="s02_03_07_01">2.3.7.1 </a>Introduction</h4>
<p>
Radiosity is a lighting technique to simulate the diffuse exchange of radiation between the objects of a scene.
With a raytracer like POV-Ray, normally only the direct influence of light sources on the objects can be calculated,
all shadowed parts look totally flat. Radiosity can help to overcome this limitation. More details on the technical
aspects can be found in the <a href="#l47">reference section</a>.
</p>
<p>
To enable radiosity, you have to add a radiosity block to the global_settings in your POV-Ray scene file. Radiosity
is more accurate than simplistic ambient light but it takes much longer to compute, so it can be useful to switch off
radiosity during scene development. You can use a declared constant or an <a href="s_95.html#s03_01_02_05_01">INI-file
constant</a> and an <code>#if</code> statement to do this:
</p>
<pre>
#declare RAD = off;
global_settings {
#if(RAD)
radiosity {
...
}
#end
}
</pre>
<p>
Most important for radiosity are the ambient and diffuse finish components of the objects. Their effect differs
quite much from a conventionally lit scene.
</p>
<ul>
<li>
<code>ambient</code>: specifies the amount of light emitted by the object. This is the basis for <a href="s_72.html#s02_03_07_03">radiosity
without conventional lighting</a> but also in scenes with light sources this can be important. Since most materials
do not actually emit light, the default value of <code>0.1</code> is too high in most cases. You can also change <a href="s_102.html#s03_03_03_02">ambient_light</a>
to influence this.
</li>
<li>
<code>diffuse</code>: influences the amount of diffuse reflection of incoming light. In a radiosity scene this
does not only mean the direct appearance of the surface but also how much other objects are illuminated by indirect
light from this surface.
</li>
</ul>
<h4><a name="s02_03_07_02">2.3.7.2 </a>Radiosity with conventional lighting</h4>
<a name="s02_03_07_02_i1">
<p>
The pictures here introduce combined conventional/radiosity lighting. Later on you can also find examples for pure
radiosity illumination.
</p>
<p>
The following settings are default, the result will be the same with an empty radiosity block:
</p>
<pre>
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
}
}
</pre>
<p>
The following pictures are rendered with default settings and are made to introduce the sample scene.
</p>
<p>
All objects except the sky have an ambient finish of 0.
</p>
<p>
The <code>ambient 1</code> 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.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="no radiosity" border="0" src="images/tutorial/radA_01.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="radiosity (default settings)" border="0" src="images/tutorial/radA_03.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="difference w/o radiosity" border="0" src="images/tutorial/radA_03a.jpg"></center>
</td>
</tr>
</table>
<p>
You can see that radiosity much affects the shadowed parts when applied combined with conventional lighting.
</p>
<p>
Changing <code>brightness</code> changes the intensity of radiosity effects. <code>brightness 0</code> would be the
same as without radiosity. <code>brightness 1</code> 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.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="brightness 0.5" border="0" src="images/tutorial/radA_04.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="brightness 1.0" border="0" src="images/tutorial/radA_03.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="brightness 2.0" border="0" src="images/tutorial/radA_05.jpg"></center>
</td>
</tr>
</table>
<p>
Changing the <code>recursion_limit</code> value leads to the following results, second line are difference to
default (<code>recursion_limit 3</code>):
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="recursion_limit 1" border="0" src="images/tutorial/radA_06.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="recursion_limit 2" border="0" src="images/tutorial/radA_07.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="recursion_limit 5" border="0" src="images/tutorial/radA_08.jpg"></center>
</td>
</tr>
</table>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="recursion_limit 1 (difference)" border="0" src="images/tutorial/radA_06a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="recursion_limit 2 (difference)" border="0" src="images/tutorial/radA_07a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="recursion_limit 5 (difference)" border="0" src="images/tutorial/radA_08a.jpg"></center>
</td>
</tr>
</table>
<p>
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.
</p>
<p>
The <code>error_bound</code> 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 <code>recursion_limit 1</code> is used.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="error_bound 0.01" border="0" src="images/tutorial/radA_09.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="error_bound 0.5" border="0" src="images/tutorial/radA_10.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="error_bound 1.0" border="0" src="images/tutorial/radA_11.jpg"></center>
</td>
</tr>
</table>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="error_bound 0.01 (difference)" border="0" src="images/tutorial/radA_09a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="error_bound 0.5 (difference)" border="0" src="images/tutorial/radA_10a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="error_bound 1.0 (difference)" border="0" src="images/tutorial/radA_11a.jpg"></center>
</td>
</tr>
</table>
<p>
Somewhat related to <code>error_bound</code> is <code>low_error_factor</code>. It reduces error_bound during the
last pretrace step. Changing this can be useful to eliminate artefacts.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="low_error_factor 0.01" border="0" src="images/tutorial/radA_12.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="low_error_factor 0.5" border="0" src="images/tutorial/radA_13.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="low_error_factor 1.0" border="0" src="images/tutorial/radA_14.jpg"></center>
</td>
</tr>
</table>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="low_error_factor 0.01 (difference)" border="0" src="images/tutorial/radA_12a.jpg"></center>
</td>
<td width="33%">
</td>
<td width="33%">
<br><center><img alt="low_error_factor 1.0 (difference)" border="0" src="images/tutorial/radA_14a.jpg"></center>
</td>
</tr>
</table>
<p>
The next samples use <code>recursion_limit 1</code> and <code>error_bound 0.2</code>. These 3 pictures illustrate
the effect of <code>count</code>. It is a general quality and accuracy parameter leading to higher quality and slower
rendering at higher values.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="count 2" border="0" src="images/tutorial/radA_15.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="count 35 (default)" border="0" src="images/tutorial/radA_13a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="count 300" border="0" src="images/tutorial/radA_16.jpg"></center>
</td>
</tr>
</table>
<p>
Another parameter that affects quality is <code>nearest_count</code>. You can use values from 1 to 20, default is
5:
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="nearest_count 1" border="0" src="images/tutorial/radA_17.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="nearest_count 5" border="0" src="images/tutorial/radA_13a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="nearest_count 10" border="0" src="images/tutorial/radA_18.jpg"></center>
</td>
</tr>
</table>
<p>
Again higher values lead to less artefacts and smoother appearance but slower rendering.
</p>
<p>
<code>minimum_reuse</code> influences whether previous radiosity samples are reused during calculation. It also
affects quality and smoothness.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="minimum_reuse 0.2" border="0" src="images/tutorial/radA_19.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="minimum_reuse 0.015" border="0" src="images/tutorial/radA_13a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="minimum_reuse 0.005" border="0" src="images/tutorial/radA_20.jpg"></center>
</td>
</tr>
</table>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="minimum_reuse 0.2 (difference)" border="0" src="images/tutorial/radA_19a.jpg"></center>
</td>
<td width="33%">
</td>
<td width="33%">
<br><center><img alt="minimum_reuse 0.005 (difference)" border="0" src="images/tutorial/radA_20a.jpg"></center>
</td>
</tr>
</table>
<p>
Another important value is <code>pretrace_end</code>. 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 <code>error_bound</code>.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="pretrace_end 0.2" border="0" src="images/tutorial/radA_21.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="pretrace_end 0.04" border="0" src="images/tutorial/radA_13a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="pretrace_end 0.002" border="0" src="images/tutorial/radA_22.jpg"></center>
</td>
</tr>
</table>
<p>
Strongly related to <code>pretrace_end</code> is <code>always_sample</code>. Normally even in the final trace
additional radiosity samples are taken. You can avoid this by adding <code>always_sample off</code>. That is
especially useful if you load previously calculated radiosity data with <code>load_file</code>.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="always_sample on" border="0" src="images/tutorial/radA_13a.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="always_sample off" border="0" src="images/tutorial/radA_23.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="always_sample off (difference)" border="0" src="images/tutorial/radA_23a.jpg"></center>
</td>
</tr>
</table>
<p>
The effect of <code>max_sample</code> is similar to <code>brightness</code>. It does not reduce the radiosity
effect in general but weakens samples with brightness above the specified value.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="max_sample 0.5" border="0" src="images/tutorial/radA_24.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="max_sample 0.8" border="0" src="images/tutorial/radA_25.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="default" border="0" src="images/tutorial/radA_13a.jpg"></center>
</td>
</tr>
</table>
<p>
You can strongly affect things with the objects' <a href="#l48">finishes</a>. 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.
</p>
<p>
Default finish values used until now are <code>diffuse 0.65 ambient 0</code>.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="diffuse 0.65 ambient 0.2" border="0" src="images/tutorial/radA_29.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="diffuse 0.4 ambient 0" border="0" src="images/tutorial/radA_30.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="diffuse 1.0 ambient 0" border="0" src="images/tutorial/radA_31.jpg"></center>
</td>
</tr>
</table>
<p>
Finally you can vary the sky in outdoor radiosity scenes. In all these examples it is implemented with a sphere
object. <code>finish { ambient 1 diffuse 0 }</code> was used until now. The following pictures show some variations:
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="ambient 0 diffuse 1" border="0" src="images/tutorial/radA_27.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="ambient 0 diffuse 0 (no sky)" border="0" src="images/tutorial/radA_26.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="yellow-blue gradient" border="0" src="images/tutorial/radA_28.jpg"></center>
</td>
</tr>
</table>
<h4><a name="s02_03_07_03">2.3.7.3 </a>Radiosity without conventional lighting</h4>
<a name="s02_03_07_03_i1"><a name="Radiosity, without conventional lighting"></a>
<p>
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.
</p>
<p>
The following 2 pictures show what changes with the scene used in part 1, when the light source is removed.
(default radiosity, but <code>recursion_limit 1</code> and <code>error_bound 0.2</code>)
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="50%">
<br><center><img alt="with light source" border="0" src="images/tutorial/radA_10.jpg"></center>
</td>
<td width="50%">
<br><center><img alt="without light source" border="0" src="images/tutorial/radB_01.jpg"></center>
</td>
</tr>
</table>
<p>
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.
</p>
<p>
The following pictures show the sample scene used in this part with different settings for <code>recursion_limit</code>
(everything else default settings).
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="recursion_limit 1" border="0" src="images/tutorial/radB_02.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="recursion_limit 2" border="0" src="images/tutorial/radB_03.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="recursion_limit 3" border="0" src="images/tutorial/radB_04.jpg"></center>
</td>
</tr>
</table>
<p>
This looks much worse than in the first part, because the default settings are mainly selected for use with
conventional light sources.
</p>
<p>
The next three pictures show the effect of <code>error_bound</code>. (<code>recursion_limit</code> 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.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="error_bound 1.8" border="0" src="images/tutorial/radB_02.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="error_bound 0.4" border="0" src="images/tutorial/radB_05.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="error_bound 0.02" border="0" src="images/tutorial/radB_06.jpg"></center>
</td>
</tr>
</table>
<p>
If there are artefacts it often helps to increase <code>count</code>, it does affect quality in general and often
helps removing them (the following three pictures use <code>error_bound 0.02</code>).
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="count 2" border="0" src="images/tutorial/radB_07.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="count 50" border="0" src="images/tutorial/radB_08.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="count 200" border="0" src="images/tutorial/radB_09.jpg"></center>
</td>
</tr>
</table>
<p>
The next sequence shows the effect of <code>nearest_count</code>, the difference is not very strong, but larger
values always lead to better results (maximum is 20). From now on all the pictures use <code>error_bound 0.2</code>
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="nearest_count 2" border="0" src="images/tutorial/radB_11.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="nearest_count 5 (default)" border="0" src="images/tutorial/radB_10.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="nearest_count 10" border="0" src="images/tutorial/radB_12.jpg"></center>
</td>
</tr>
</table>
<p>
The <code>minimum_reuse</code> 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
calculations.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="minimum_reuse 0.001" border="0" src="images/tutorial/radB_13.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="minimum_reuse 0.015 (default)" border="0" src="images/tutorial/radB_10.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="minimum_reuse 0.1" border="0" src="images/tutorial/radB_14.jpg"></center>
</td>
</tr>
</table>
<p>
In most cases it is not necessary to change the <code>low_error_factor</code>. This factor reduces the error_bound
value during the final pretrace step. <code>pretrace_end</code> was lowered to <code>0.01</code> in these pictures,
the second line shows the difference to default. Changing this value can sometimes help to remove persistent
artefacts.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="low_error_factor 0.01" border="0" src="images/tutorial/radB_15.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="low_error_factor 0.5 (default)" border="0" src="images/tutorial/radB_16.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="low_error_factor 1.0" border="0" src="images/tutorial/radB_17.jpg"></center>
</td>
</tr>
</table>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="low_error_factor 0.01" border="0" src="images/tutorial/radB_15a.jpg"></center>
</td>
<td width="33%">
</td>
<td width="33%">
<br><center><img alt="low_error_factor 1.0" border="0" src="images/tutorial/radB_17a.jpg"></center>
</td>
</tr>
</table>
<p>
<code>gray_threshold</code> 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 <code>gray_threshold</code>. 1.0 means no color in radiosity at all.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="gray_threshold 0.0 (default)" border="0" src="images/tutorial/radB_10.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="gray_threshold 0.5" border="0" src="images/tutorial/radB_18.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="gray_threshold 1.0" border="0" src="images/tutorial/radB_19.jpg"></center>
</td>
</tr>
</table>
<p>
Another important parameter is <code>pretrace_end</code>. 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
slower rendering.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="pretrace_end 0.2" border="0" src="images/tutorial/radB_26.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="pretrace_end 0.02" border="0" src="images/tutorial/radB_27.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="pretrace_end 0.004" border="0" src="images/tutorial/radB_28.jpg"></center>
</td>
</tr>
</table>
<p>
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.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="ambient 3 instead of ambient 0 for one object" border="0" src="images/tutorial/radB_23.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="ambient 0.5 instead of ambient 0 for all objects sky: ambient 0" border="0" src="images/tutorial/radB_24.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="error_bound 0.04 recursion_limit 2" border="0" src="images/tutorial/radB_25.jpg"></center>
</td>
</tr>
</table>
<p>
Finally you can strongly change the appearance of the whole scene with the sky's texture. The following pictures
give some example.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="yellow-blue gradient from left to right" border="0" src="images/tutorial/radB_20.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="light-dark gradient from left to right" border="0" src="images/tutorial/radB_21.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="light-dark gradient from bottom to top" border="0" src="images/tutorial/radB_22.jpg"></center>
</td>
</tr>
</table>
<p>
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
situations.
</p>
<pre>
global_settings {
radiosity {
pretrace_start 0.08
pretrace_end 0.01
count 500
nearest_count 10
error_bound 0.02
recursion_limit 1
low_error_factor 0.2
gray_threshold 0.0
minimum_reuse 0.015
brightness 1
adc_bailout 0.01/2
}
}
</pre>
<p>
<img alt="Higher quality radiosity scene" border="0" src="images/tutorial/radB_X.png">
</p>
<h4><a name="s02_03_07_04">2.3.7.4 </a>Normals and Radiosity</h4>
<a name="s02_03_07_04_i1">
<p>
When using a <a href="#l49">normal statement</a> in combination with radiosity lighting, you will see that the
shadowed parts of the objects are totally smooth, no matter how strong the normals are made.
</p>
<p>
The reason is that POV-Ray by default does not take the normal into account when calculating radiosity. You can
change this by adding <code>normal on</code> to the radiosity block. This can slow things down quite a lot, but
usually leads to more realistic results if normals are used.
</p>
<p>
When using normals you should also remember that they are only faked irregularities and do not generate real
geometric disturbances of the surface. A more realistic approach is using an <a href="#l50">isosurface</a> with a
pigment function, but this usually leads to very slow renders, especially if radiosity is involved.
</p>
<table border="0" cellpadding="0" cellspacing="2" class="nofloat" width="100%">
<tr>
<td width="33%">
<br><center><img alt="normal off (default)" border="0" src="images/tutorial/radC_01.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="normal on" border="0" src="images/tutorial/radC_02.jpg"></center>
</td>
<td width="33%">
<br><center><img alt="isosurface" border="0" src="images/tutorial/radC_03.jpg"></center>
</td>
</tr>
</table>
<p>
You can see that the isosurface version does not have a natural smooth circumference and a more realistic
shadowline.
</p>
<h4><a name="s02_03_07_05">2.3.7.5 </a>Performance considerations</h4>
<a name="s02_03_07_05_i1">
<p>
Radiosity can be very slow. To some extend this is the price to pay for realistic lighting, but there are a lot of
things that can be done to improve speed.
</p>
<p>
The radiosity settings should be set as fast as possible. In most cases this is a quality vs. speed compromise.
Especially <code>recursion_limit</code> should be kept as low as possible. Sometimes <code>1</code> is sufficient, if
not <code>2</code> or <code>3</code> should often be enough.
</p>
<p>
With high quality settings, radiosity data can take quite a lot of memory. Apart from that the other scene data is
also used much more intensive than in a conventional scene. Therefore insufficient memory and swapping can slow down
things even more.
</p>
<p>
Finally the scene geometry and textures are important too. Objects not visible in the camera usually only increase
parsing time and memory use, but in a radiosity scene, also objects behind the camera can slow down the rendering
process.
</p>
<p>
<a name="l47">
<small><strong>More about "reference section"</strong></small>
</a>
<ul>
<li><small>
<a href="s_103.html#s03_03_04">3.3.4 Radiosity</a> in 3.3 Scene Settings
</small>
<li><small>
<a href="s_165.html#s03_08_13_01">3.8.13.1 Radiosity</a> in 3.8.13 Global Settings
</small>
<li><small>
<a href="s_72.html#s02_03_07">2.3.7 Radiosity</a> in 2.3 Advanced Features
</small>
</ul>
</p>
<p>
<a name="l48">
<small><strong>More about "finishes"</strong></small>
</a>
<ul>
<li><small>
<a href="s_117.html#s03_05_03">3.5.3 Finish</a> in 3.5 Textures
</small>
<li><small>
<a href="s_162.html#s03_08_10_06">3.8.10.6 Finish</a> in 3.8.10 Texture
</small>
</ul>
</p>
<p>
<a name="l49">
<small><strong>More about "normal statement"</strong></small>
</a>
<ul>
<li><small>
<a href="s_116.html#s03_05_02">3.5.2 Normal</a> in 3.5 Textures
</small>
<li><small>
<a href="s_162.html#s03_08_10_05">3.8.10.5 Normal</a> in 3.8.10 Texture
</small>
<li><small>
<a href="s_69.html#s02_03_04_02">2.3.4.2 Normals</a> in 2.3.4 Advanced Texture Options
</small>
</ul>
</p>
<p>
<a name="l50">
<small><strong>More about "isosurface"</strong></small>
</a>
<ul>
<li><small>
<a href="s_108.html#s03_04_04">3.4.4 Isosurface Object</a> in 3.4 Objects
</small>
<li><small>
<a href="s_68.html#s02_03_03_03">2.3.3.3 Isosurface Object</a> in 2.3.3 Other Shapes
</small>
</ul>
</p>
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<strong>2.3.7 Radiosity</strong>
</td>
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