archkre

Introduction

VIZ 4 offers three methods to render the Radiosity solution: Re-use Direct Illumination, Render Direct Illumination and Regather.

Regather re-processes the Radiosity solution for each pixel, randomly shooting rays on the scene to re-sample the lighting level of each pixel. The more samples shot, the more precise regather will be.

Regather also offers a filter, which blends the lighting level of the surrounding pixels, giving you a better image without needing to use a higher number of rays.

In some cases, these random rays will “see” a very bright polygon, and then they will produce spikes, or bright white pixels on the image. For this reason, Regather allows you to clamp these bright pixels, limiting them to a valid range.

Let’s see how these controls work and how to better optimize them for your images.

Regather Controls

1. Open regather.max
2. Rendering > Radiosity…
3. Hit Start to process Radiosity
4. Render the scene

Notice this scene is already ready for processing, meshing is on, but Initial quality is 0.1. Also, filtering is 0.



Instead of fixing the column and the wall using the meshing techniques and rerunning the radiosity system, we will instead use Regather to render this image.

5. Select Render Direct Illumination
6. Turn on Regather and specify 5 Rays per Sample
7. Render the image

Notice the image is pixelated and contains several white dots:



The white dots happen because Regather is “seeing” the white self-illuminated area of the spots, and since that area is very bright, it creates a lighting level out of range. To solve it, we’ll use clamping.

8. Turn on Clamping and enter 100 in Clamp Values
9. Change the render type to Region and render a small square on the wall, to the left of the column.

It clamped too much, to the point that there’s no indirect illumination now:



10. Enter a value of 1000 in Clamp Values and click Render Last.

You now have Indirect Illumination back, but if you zoom in the rendered area, you’ll still notice some white dots:



11. Enter a value of 500 in Clamp Values. Change Render Type to View and click Quick Render

Now you got the right balance:



Now that you got rid of the spikes, we need to remove the graininess. This is done by balancing the Number of Samples and the Filter Radius.

12. Set Filter Radius to 10 and re-render.


This got rid of the grains in the image:



If you render a higher resolution, you will notice that you need to increase the number of samples or the filter radius, so the image retains its quality.

13. Select the Floor Object
14. Right-Click and select Properties
15. On the Radiosity Tab, turn on Exclude from Regather.
16. Do the same for the Ceiling
17. Render the image

Note it will render a lot faster, since Regather is not processed on those objects. This is a trick to process Regather only where it’s needed, speeding up the render.

The objects excluded from Regather will process as Direct Illumination, so make sure they render without artifacts.

Tips and Tricks

· Lights will be scanline rendered with Regather, since it only works with Render Direct Illumination. If you want to Re-Use Direct Illumination on your lights, make sure you set them to Store Direct Illumination. This will render them Re-Using Direct Illumination, and will still perform Regather.

· Use Region Render to try the values, since it will only render part of an image.

· Exclude objects from regather, to make it faster.

Summary

This tutorial explained you how Regather settings work.

Regather is time consuming, but allows you to save time on modeling specifically for radiosity, reduces processing time for the solution and meshing creation.