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Setting up and rendering illumination in Brazil r/s.

Part 1. Brazil tools review


Light Sources

They are undoubtedly the most important factor for setting up illumination. But we shall review in detail only those parameters, which concern indirect illumination.

Brazil offers light sources for all main source types in 3ds max plus two area light sources. Thus, we have 5 light sources: omni, spot, directional, rectangle area, and disk area. The main advantage of light sources in brazil is their capacity to emit photons.

In light source settings you can separately enable/disable different illumination types – direct and indirect. Thus, you can enable illumination type calculations in three places in brazil – from the light source control panel (in two places) and from the render control panel. This is certainly a very flexible approach. Nevertheless, if you forget to enable a light type at least in one place, it will not be calculated. Taking into account that the control panels are scattered in various places of the interface, it's not very convenient to control.

All light sources can be photometric and they can use real physical illumination parameters, such as 3D illumination distribution and illumination intensity units. Indisputable advantage of brazil is its built-in IES file viewer.

If photometric lights are not used, illumination brightness is set on the Color/Projector tabbed page. Here you can set the illumination intensity and its color.

When calculating illumination from light sources, their emission type is taken into account. We should dwell on area lights, as they possess the diffuse emission type – illumination from each area light will depend not only on the distance, but also on the angle between the direction to the area light and the normal of the point, where the illumination is calculated. Illumination from area lights is based on subdividing their surfaces into a grid of areas. Each area is sampled by one or several rays. Illumination in a point is a total of sample illuminations for the light source areas visible from that point. There are two main algorithms in brazil to calculate samples – Regular and Adaptive Halton, which are available on the Area Light Options tabbed page.

Pic. 22 Area Light Options.

Regular uses a constant number of samples, Adaptive Halton changes the sample number depending on illumination conditions. For example, when part of the light source is blocked by an object, more samples can be used in the border area.

Initial start – specifies the initial number of samples. It remains constant for Regular and can be changed for adaptive sampling. The 1 and higher values are recommended for regular, for adaptive sampling – small initial start values within 0.1 or lower.

Error estimator – the way to estimate an error in calculating illumination. There are three types – mono, RGB, and HDRI. Mono is faster, but it can result in noises in colored shadows or when illuminated by a colored texture. RGB guarantees that the error will not exceed a specified value in all color channels. HDRI is more accurate in estimating the error in shadows and it's the slowest of the three error estimators.

Max samples – maximum possible number of samples, this number cannot be exceeded no matter how the adaptive sampling is configured.

Estimate intrvl – interval for calculating the sampling error. The larger the interval is, the more accurate and the slower the error will be calculated.

Max error – the main setting that enables additional sampling and determines the quality of illumination calculation. It is a ratio percentage of the error value to the global illumination value. For a final render you'd better use the Max Error of 0.1% and lower in combination with high max samples, about 1000 or even higher. Max error can be high for a preview, up to 100%.

As area lights may considerably slow down calculations, spot lights can be used as their alternative, as they can also emit photons and brazil allows to calculate shadows for these lights as well, like for area lights.

Calculating indirect illumination is based on real physical laws, that's why the choice of attenuation type together with the choice of real units and real geometry sizes is crucial. Attenuation type can be selected on the Attenuation / Decay tabbed page.

Pic. 23 Attenuation Type Selection.

Decay>Auto is used for photometric light sources, ON allows to select the quadratic Inverse Square attenuation from the drop-down list (you should use this attenuation) or distance-proportional attenuation, OFF completely disables attenuation.

The Attenuation group also allows to specify clipping planes of the illuminated scene area. In this case the illumination will be only between the selected planes, which is convenient to cut down the calculation time.

In case of the Inverse Square attenuation you should also specify the initial point relative to the light source, from which the attenuation will start, and Scale, which allows additional scaling of selected units. If real units are selected, Scale can be set to 1 and the illumination can be controlled by its intensity and energy (for photons) settings. Or you can leave intensities and energies alone, and increase the Scale value instead. The latter method is more convenient, and besides, changes in illumination intensity are displayed in the Max workplace.

And finally, the Photon Maps tabbed page.

Pic. 24 Settings of properties and quantities of photons emitted by a light source.

That's the place where you should specify the type of emitted photons, Caustic or Global, the number of photons emitted, and their energy. This tabbed page also houses additional photon emission parameters. But as developers are not sure whether these settings will be retained in the next brazil version, we shall not review them and will limit ourselves to default photon emission settings.


Igor Sivakov (igsiv@mail.ru)

December 2, 2004

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