This tip will focus on a single new technology that has been added to the renderThinking renderer, called “Final Gather.” Although the title of the feature is a bit esoteric, the net result is a way to very quickly and efficiently simulate many of the effects of Radiosity light transport in standard renderings. Unlike the full Radiosity rendering option in renderThinking, Final Gather only does “one bounce” radiosity and sacrifices some precision for increased speed, but the effects can be incredibly realistic and in many cases just the trick for higher realism.
As the image animation to the right illustrates, adding Final Gather to the “rendering chain” (what is computed before and after rendering to make the image) of certain scenes can dramatically enhance the realism and illumination of surfaces and objects. To start with, you can see in the illustration that simply Raytracing the “Cornell Box” in the scene provides a fairly dark image, with black shadows and grey walls (that are actually white). This image took about 5 seconds to render on a fairly slow computer.
By going into the Rendering tab of the Shading panel in sT 7.5 or 7.6, and simply adding “Final Gather” to the render, the side walls “bleed” their bright colors onto the white surfaces and the illumination from the point light at the top of the box reaches even into the shadow regions because it “bounces” off of the walls – just as real light would. Adding this irradiance to the scene (with the default quality settings) meant that the image took about 6 seconds to render. A very small increase in rendering time for a very large increase in lighting realism!
The last image in the animation (Final Gather “ON” (more precise)) shows the possible refinement of the scene by doubling the Number of Rays cast by Final Gather in the scene, and by decreasing the size of the samples so that they can detect smaller changes in color in the scene. The results are the fairly subtle brightening of the walls where the white squares on the floor touch the walls and objects (while the black squares bounce no light), and the smoother gradations of shading on the walls and on the sphere in particular. Changing these settings meant that the render time went from 6 seconds (at the default settings) to 20 seconds for this very simple scene. (Each scene will be different, but in general, this is much faster than using the full Radiosity render option!)
In addition to being able to “tweak” the Final Gather settings to increase precision or calculate things like specular bounce (for very shiny surfaces), there are also very simple adjustments for the saturation of the irradiance (for example, so the blue and red walls do not overly “color” the scene as in my example), and also for the overall brightness of the Final Gather effect (to make the irradiance more dramatic or more subtle). These simple additional adjustments also do not change the time it takes to render the scene with Final Gather on!