This page provides information on the Photon Map rollout in the Render Settings.

 

Page Contents

 

Overview


This rollout is accessible when Photon map is selected as the Engine for Primary bounces or Secondary bounces in the GI rollout. See the Photon Map GI topic for information on how this option works.

 


 

UI Path: ||Render Settings window|| > GI tab > Photon map tab 
(When Photon map is selected as a GI engine) 


Photon Map Parameters


The building of the photon map is also controlled by the photon settings of individual lights in the scene. See the Light Attributes for more information on how to control the number of emitted photons for Maya lights. All V-Ray lights have built-in controls for this.

Bounces  – Controls the number of light bounces approximated by the photon map. More bounces produce a more realistic result, but take more time and memory.

Max photons – Specifies how many photons will be taken into consideration when approximating the irradiance at the shaded point. More photons mean a smoother (and more blurry) result and may also slow down the rendering. Smaller values mean a more noisy result but will render faster. When this value is 0, V-Ray will use all the photons in the given search range.

Store direct light  – When this option is enabled , V-Ray will store direct illumination in the photon map as well. This may speed up the irradiance map or brute force GI when used as a primary engine, especially when there are lots of lights in the scene. When this option is enabled , direct lighting will be computed always by tracing the necessary rays. This may slow things down if there are lots of lights in the scene.

Auto search dist – When this option is enabled, V-Ray will try to compute a suitable distance within which to search for photons. Sometimes the computed distance is okay, in other cases it might be too big (which will slow down the rendering) or too small (which will produce a more noisy result).

Search Distance – This option is only available when  Auto search dist  is off. It allows you to specify the photon search distance manually. Keep in mind that this value depends on the size of your scene. Lower values will speed up the rendering but may produce more noisy results. Larger values will slow down the rendering but may produce smoother results.

Multiplier  – Controls the brightness of the photon map.

Max density  – Limits the resolution (and thus the memory) of the photon map. Whenever V-Ray needs to store a new photon in the photon map, it will first look if there are any other photons within a distance specified by  Max density . If there is already a suitable photon in the map, V-Ray will just add the energy of the new photon to the one in the map. Otherwise, V-Ray will store the new photon in the photon map. Using this option allows you to shoot many photons (and thus get smoother results) while keeping the size of the photon map manageable.

Mode 

Mode  – Sets the rendering mode of the light cache: 

New Map – Computes a new photon map for each frame of an animation. 
From file  – In this mode, the photon map is loaded from a file.  The photon map file does not include the prefiltering of the photon map; prefiltering is performed after the photon map is loaded, so that you can adjust it without the need to recompute the photon map.  

File Name  – Specifies the file name to load the photon map from, when the  Mode  is set to  From file .

Save  – Saves the photon map to a file on disk for later re-use. Note that the  Don't delete option must be on for this to work; otherwise, the photon map will be deleted as soon as rendering is complete and it will not be possible to save it.

On Render End

This group of controls determine what happens with the photon map after rendering is complete.  

Don't delete – When enabled (the default), the photon map remains in memory after the rendering. Turn this option off to automatically delete the photon map (and thus save memory). 

Auto save  – When  enabled, the photon map will be automatically written to the specified file. Note that the photon map will be written as soon as it is calculated, rather than at the actual end of the rendering. 

Auto Save File – Specifies the file name to save the photon map to.

 

 

Photon Map Advanced Parameters  


Prefilter  – When this option is enabled, the samples in the Photon Map are filtered before rendering. Note that this is different from the normal photon map filtering which happens during rendering. Prefiltering is performed by examining each sample in turn, and modifying it so that it represents the average of the given number of nearby samples thus creating a collection of points in 3d space along with the computed indirect illumination at those points.

Prefilter samples – Controls the number of samples taken during prefiltering. Larger values produce smoother results, but may be slower; smaller values produces more noisy results but rendering is faster.

Convex Hull Estimate – When this option is disabled V-Ray uses a simplified algorithm for computing the area, taking the distance to the farthest photon and spreading photons evenly over the area. This approach can cause corners to be darker than expected. When this option is enabled, more photons are shot into dark corners, lightening up the corners. This approach is slower and not as robust.

Retrace threshold  – When this value is greater than 0.0, V-Ray will use the Brute Force method GI near corners instead of the Photon map method in order to obtain a more accurate result and to avoid splotches in these areas. This can slow down the rendering. When this is 0.0   , the Photon map method will be used always, which will be faster but might produce artifacts near corners or in places where objects are close to each other.

Retrace Bounces – Controls how many bounces will be made when retracing corners. If  Retrace Corners  is 0.0, then this parameter is ignored. Typically this should be equal to the  Bounces  parameter.

 

 

Notes


  • The photon map cannot simulate secondary illumination from skylight. The photon map is mostly useful for interior scenes with artificial lighting or relatively small windows.