Rendering a static scene from multiple views

Search Keywords: IR, Irradiance map, GI

In this tutorial we will examine ways to efficiently render a static scene from multiple views.

This is the scene we will use for the tutorial:

We want to efficiently render several views of this scene, using the irradiance map.

The different irradiance map modes will help us in this task.

First open the starting scene.

By default the irradiance map mode is set to Single frame. This allows us to render the scene from any view, but every time the irradiance map will be computed from scratch. There are two cameras in the scene. Render each of them:

We could render a single view, save the irradiance map, and tell V-Ray to use that map, instead of computing a new one the next time. Since the irradiance map from the last rendering is still in memory (we have the Don't delete option in the On render end group set), all we have to do is open the Advanced irradiance map parameters rollout and click the Save to file button. Choose a file name, for example "test", and save the irradiance map.

Now that we have map saved to disk, we have to tell V-Ray to use that map. Change the irradiance map mode to From file, click the Browse button and select the file we just saved. Re-render the image. Notice that now V-Ray does not calculate an irradiance map, but skips directly ahead to the rendering.

Since no irradiance map is computed, the rendering is very fast. What if we want to render the first view at this moment? This is what happens:

Clearly this is not what we want, but why does it happen? The irradiance map is only partially view-independent - meaning that a single sample in the irradiance map is valid for any view, but the samples for a given view are optimally generated for that view only. V-Ray will not calculate the irradiance map for parts of the scene that are out of view. If you check the Show samples option in the Indirect illumination rollout and render the scene, you can see where the actual samples are:

Is it possible to render this new view using the old samples and add new ones only where it is necessary? The answer is "yes". Just set the irradiance map mode to Incremental add to current map. Remember that the current irradiance map is still in memory. Render the view: