<sect2 id="sect-gui-rendopt4">
    
 
 <title>The render options box : photons tab</title>
  
     <figure id="fig-interface-rendopt4">
        <title>The photon tab.</title>
        <screenshot>
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              <imagedata fileref="figures/interface_rendopt4.png" format="PNG" />
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            <textobject>
              <phrase></phrase>
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      </figure>


<para>
Here are options relative to photons tracing method.

<para><guilabel>Spacing and count</guilabel></para>
<para>
 The number of photons generated can be set using either the spacing or count keywords:
<para>
  <itemizedlist>
  
    <listitem>
     If spacing is used, it specifies approximately the average distance between photons on surfaces. If you cut the spacing in half, you will get four times as many surface photons, and eight times as many media photons.  
    </listitem>

    <listitem>
  If count is used, POV-Ray will shoot the approximately number of photons specified. The actual number of photons that result from this will almost always be at least slightly different from the number specified. Still, if you double the photons_to_shoot value, then twice as many photons will be shot. If you cut the value in half, then half the number of photons will be shot.
  	<itemizedlist>
  
    	<listitem>
 It may be less, because POV shoots photons at a target object's bounding box, which means that some photons will miss the target object.
	</listitem>

    	<listitem>
 On the other hand, may be more, because each time one object hits an object that has both reflection and refraction, two photons are created (one for reflection and one for refraction).
	</listitem>

    	<listitem>
 POV will attempt to compensate for these two factors, but it can only estimate how many photons will actually be generated. Sometimes this estimation is rather poor, but the feature is still usable.
	</listitem>
  	</itemizedlist>

   </listitem>
  </itemizedlist>
</para>
</para>


<para><guilabel>Gather</guilabel></para>
<para>
 
</para>


<para><guilabel>Media photons</guilabel></para>
<para>
 
</para>



<para><guilabel>Jitter</guilabel></para>
<para>
 
</para>

<para><guilabel>Max tracel level and ADC bailout</guilabel></para>
<para>
 
</para>

<para><guilabel>Radius</guilabel></para>
<para>

  
</para>



<para><guilabel>Autostop</guilabel></para>
<para>
 
</para>


<para><guilabel>Adaptive Search Radius</guilabel></para>
<para>
 
</para>


</para>
</sect2>



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