Improving normal map on billboards

To enhance lighting of objects in dynamic virtual environments, maps that contain information about normal of every texel of a surface of a model are being created. Those are called normal maps. Silvador also generates normal maps. They look like this:

If we look at the trunk, it looks fine, there is not much to be improved - it just matches the geometry the texture represents. But if we look at the crown that consist of more-or-less randomly rotated leaves, its worse - there just appears to be something that resembles a white noise. There is no structural information about the crown whatsoever. And if we use it for shading, the result corresponds to that, it is flat. If there would not be for the trunk, we couldn't say what direction a light is coming from.

In Silvador since version 1.53 there is a new option, by default on for billboards, it is called VisualizerLOD2.polyplaneCrownAwareNormalMap. It influences the way normal map is calculated. It also considers original normal of a leaf just as the original approach, but weights it by the visibility of given point from given direction. That means that normals tend to point more to direction they are visible from. We calculate the adjusted normal iteratively using this formula:

      M = normalize(sum(for x from <0, n>)(shadowCoef * max(dot(N, Lx), 0) * Lx))

, where:

      N - normal vector of the surface

      L1..Ln - individual vectors of light contribution (possibly shaded)

      M - adjusted normal, respecting visibility of given point

The difference is significant. Following 2 images demonstrate difference without and with the crown-aware normal map:

There is suddenly much more low-frequency information present in the normal map. Normals on the left side of the crown tend to point left and on the right side to the right. This is what will give the tree crown a spherical shape after lighting is applied. This is how you can see the result lit in the virtual environment of VBS Blue (original normal map, crown-aware normal map):

If we look at the tree crown on the right image, we don't have a problem to identify what direction is light coming from, unlike the left image.

Overview of generated maps

Let's recapitulate what all maps Silvador can generate at the moment:

Albedo RGB / Alpha:

 

Macro RGB / Alpha:

 

Normal: