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photon map
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photon map

photon map stores indirect illumination by tracing photons and storing their surface hit positions with the carried illumination into a point cloud. Illumination in a surface point is then computed by finding and averaging the closest photons. photon map has the controls described below. The frequently needed controls are available on the toolbar, and the rest can be found from the property window.

  • Photon Count: - The number of photon-surface hit points stored in the map

  • Brightness: - The brightness of the photon map illumination

  • Sampling: - The number of closest photons used for evaluating illumination in the examined point. Increasing the value reduces noise, but makes the illumination less detailed and also slower to render. A typical Sampling value for a high quality photon map is 100-1000.

  • Radius: - Limits the search radius when the closest photon set defined by the Sampling value is collected. The program automatically maintains a reasonable radius value (it is updated when the Sampling rate changes). The user can manually adjust the automatic value. Decreasing the value makes rendering faster, but may increase noise in areas where photon density is low. Increasing the Radius value may sometimes fix rendering errors visible in a photon map.

  • Sharpen Shadows: - A filtering option, which prevents incorrect illumination spreading from bright areas to strongly shadowed areas. The option is not available for pre-filtered photon maps.

photon map illuminated interior scene. Courtesy of Pixel Perfect.

Filter Tool

Illumination of a photon map can be preprocessed using the Filter tool. This tool evaluates the illumination defined by the photon map at the actual photon positions. This is done by averaging data typically from hundreds of nearby photons, which is a time consuming process. After pre-filtering, illumination can be resolved from a small number of closest photons. Therefore, pre-filtering tool is a great time saver for camera animations in static scenes, and also for single images if the number of photons is clearly smaller than the number of image pixels.

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