The Environment Map

The environment map describes the world which surrounds the model, in particular, the lighting from the environment

Now it is time for the main course of the assets.

An environment map is needed to describe the world outside of the object. For this example, as there are no lights in this demo, the environment map must contain all incoming energy in order to have a realistic result. This means it must be unclipped.

What is an unclipped map?

Without going into photographic technicalities, to produce an unclipped image the photographer must have used as many stops as necessary, in other words, take darker and darker pictures of the scene until even the sun will not "burn" the photograph. The reason for this is that the different areas of the scene require different exposures to accurately capture their actual brightnesses. For example, taking only a single exposure of a room with a bright window and a dark corner could lead to either the window being "blown out" (over exposed) or the dark corner being completely black (under exposed). In both cases the actual incoming energy is not accurately captured.

In an unclipped map, it is possible to have values as small as a millionth and high as a few hundred thousand. These large values would be found if the sun is present in the scene, but in reality it all depends on the contrast when seen naturally. There will be more on this later.

Usually, these images will be calibrated in such a way as to make a majority of the scene clearly visible, meaning to a viewer the very-dark parts will display as black and very-bright parts as a saturated colour. But, the information is actually there, increasing the exposure will reveal the details in dark places, and decreasing exposure will show details in bright places.

The image below is unclipped. Move the slider at the bottom to decrease the exposure and reveal the details of the stage.

For the pipeline in the demo, the most important feature of unclipped maps is that they capture the "real" incoming light from the scene, not just the apparent image. In other words the energy rather than just the perceived colour.

In this section the various steps required to create an environment map for this demo are explained in detail. In particular, there is a discussion of how to choose an image format for the unclipped environment map and a demonstration of how to use PVRTexTool to convert the initial environment map image into a cubemap.