Final gathering is a way of calculating indirect illumination without using photon energy. Instead of using rays cast from a light to calculate illumination, final gathering uses rays cast from each illuminated point on an object’s surface. The rays are used to sample a hemisphere of a specified radius above each point and calculate direct and indirect illumination based on what the rays hit.
The overall effect is that every object in the scene becomes a “light source”, at least to some extent, and influences the color and illumination of the objects and environment surrounding it.
You can combine direct illumination and/or global illumination with final gathering to increase photorealism in your scenes. Used in the correct way, final gathering can create stunning, photorealistic lighting in a fraction of the render time needed for global illumination alone.
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It is important to remember that the lighting created by final gathering and direct illumination are added together, meaning that a scene which uses both direct illumination and final gathering will be brighter than a scene which uses either one or the other. |
Pros and Cons of Final Gathering
Final gathering has advantages and disadvantages:
Advantages
• Because it uses fewer photons, scenes render faster and use less memory when creating the Photon Map.
• Final gathering is more accurate than a direct photon map lookup. Accuracy is most noticeable on the edges of objects and in corners.
Disadvantages
• If you do not use global illumination, photorealistic results take much longer to render.
• When using global illumination and a high Accuracy setting, the render can take longer than it would without final gathering; however, the slower the render, the higher the quality.
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