Previously, we saw how to manage an Image Map texture in the Texture Editor. The power of textures is that they can be used for many different effects. In the simplest of cases, a texture provides the “paint coat” of a surface. A texture can, for example, give the appearance of denim to a sculpted pair of pants. Change the texture and they can look like leather. We are simplifying, of course, but that’s the gist of what textures can do.

There is another application of textures. They can provide numeric data for calculation of special effects. For example, if we want to create shading that simulates pores on the skin, we would know that pores are recessed areas of the surface, little dents. If we observe how we perceive dented areas of a surface, whether we are talking about skin,  a wall, or a piece of metal, those dents are visible because they create a darker area in the surface. In fact, a common “rejuvenating” trick of photography is to blast a lot of bright, frontal light to an aging face. Without need for layers of makeup, the frontal light removes the lines caused by wrinkles and the subject looks immediately ten years younger.

If we think of how we would draw wrinkles on a face, using a pencil, we know that we would draw some darker lines. The same principle is behind bump mapping. The term is a bit misleading, because the effect is not focused on just rendering bumps. The idea is to simulate the imperfections of a surface by simulating the shading of light as if the surface had physical bumps and dents. A bump map is a grayscale texture, it can be an image file or a computer-calculated pattern, that is used to simulate such “imperfections.” Given that almost no surface in nature is completely flawless, a bump map, even a subtle one, can add a lot of realism to our scenes.

A bump map is a grayscale pattern. The idea is that the bump map gives a value for each pixel that it represents, and that value is used to determine the height of that point in the surface that is rendered. A value could represent a dent (negative bump), a bump (positive bump), or a flat point (neutral bump). So, if, for example, we decide to use 0.0 for the negative bump, 1.0 for positive and 0.5 for neutral, all we need to do is to find a way of mapping those values into an image. Poser and DAZ Studio artists are used to colors being expressed in integral values, from 0 to 255, instead of  fractional ones. No problem there. 0.0 is 0 (zero), 0.5 is equivalent to 127 (255/2) and 1.0 is equivalent to 255. All the other values will be easily mapped with a simple division. For example, 0.25 is 255/(1.0/0.25) or 63.75 => 64. Let’s verify: 0.25 x 4 = 1.0, 63 x 4 = 256, clamped to 255. Good enough. In real life the software actually uses the fractional values, which lead to higher accuracy. I converted the numbers to integers just to show how this works in the a more familiar territory.

The point here is that, with a bump map, we don’t need a triplet of values, like in RGB, we only need one value per point in the map. So, the same value, whatever that is, is used for each RGB channel. When we make a bitmap where each pixel has the same value for Red, Green, and Blue, we end up with a grayscale image. The renderer will simply extract the value from one channel, let’s say that it’s the Red one, and use it to calculate if, at the given point, there is a dent, a bump, or no alteration at all.

The following image shows a sphere, a bump map and the effect of applying that bump map to the sphere.

Bump map example form Wikipedia, by Brion Vibber, McLoaf, GDallimore

The bumps or dents are simply painted on, they are not really altering the elevation of the surface. Therefore there are limits to the usefulness of this technique. For example, bump mapping works well when the camera is fairly perpendicular to the surface. It’s much less convincing when looking at the edges of the model. Nevertheless, bump mapping is a very useful technique that is in use today and it can provide an additional level of realism while being pretty fast to render.

You can apply a bump map to a material in Reality by using the Modifiers tab. The first texture in the panel is for a Bump map or a Normal map, which we will examine later.

I hope this was useful. We will continue our discussion of materials next week, stay tuned!


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