Enable GI - On by default, there is only one choice of type currently: Monte Carlo
There are groups of settings for Monte Carlo Global Illumination.
- Intensity - A multiplier applied to overall GI brightness. Useful especially for interior scenes. GI is a type of illumination and like other lights, its intensity can be modified. However only an intensity of 100 % is close to physically accurate.
- Rays - It is the number of brute force rays to use per pixel sample when not using interpolated or in regions of interpolated GI when interpolated samples could not be generated.
Caustics - Generally, a caustic occurs in the real world when light reflects off a curved surface or refracts through a transparent surface so that it is focused on a small area. Light through a wine glass is a good example. With a more complex surface, the caustic can create a random pattern like those seen on the floor and sides of a swimming pool. Switching Caustics on here will generate accurate caustics rather than the approximations seen in previous versions.
From left: Caustics in a brute force render; Caustics in an interpolated render with Minimum Spacing at 2, Maximum Spacing at 64; more evident Caustics with Min at 1 and Max at 5.
- Sample Backdrop - Whether or not to sample the backdrop at all.
Include Page Sampling BG and GI Sampling BG and GI
- ISBG Sampling - Enables the importance sampled background (ISBG) samples below. This reduces noise when using an HDR backdrop image to illuminate the scene and also makes the illumination far more accurate. Specifically, it will examine very bright hot-spots to help generate more accurate lighting/shading from those hot-spots.
ISBG Samples - Sets the number of importance samples for the image.
ISBG can slow down interactivity in some situations. If you try to change the backdrop image with VPR active it must be recalculated every time you change it, so if you are going to change images, switch back to OpenGL to do it.
- Affected by Volumetrics - Allows volumetrics to be included in the global illumination calculation. This can slow rendering but is more accurate if there are volumetrics in the scene.
When you engage the Interpolated button, new settings become available.
Minimum Pixel Spacing (1) and Maximum Pixel Spacing (100) shown with the size of the cells changing
Caching saves Global Illumination data for subsequent render passes and frames, which can significantly reduce rendering time. The results can be inaccurate if objects or lights are animated, but this option works particularly well with scenes like a walk-through in which only the camera moves.