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We are all used to normal lights, but Poser also allows us to create negative lights that subtract light from our scene. These lights can be a very powerful tool. Here we will look at the some of the basic features of the negative light.
Figure One shows us a simple ball, lit by one white infinite light.
Figure Two shows us the same ball, but this time we have added a second light, placed it in the back-right of our scene, and set it to be a negative light. The result is that the back of the ball is now much darker than in figure one.
Like so many good things in Poser, we create our negative lights in the material room. Figure Three shows the negative light used to produce Figure Three. The only thing we need to do to create a negative light is to set the Intensity of our light to a negative number. Here I have chosen -1, so our negative light has the same strength as our normal light.
Figure four shows what happens when our negative light is coming from a similar direction to the normal light. This time part of the specular highlight has also disappeared, where it overlaps with the negative specular highlight.
Just as we can have specular only lights, we can also have specular only negative lights (or diffuse only negative lights). To to this, we create our negative light as normal, but then set the Diffuse colour to black. Figure 5 shows the result of adding the light shown in Figure 6. Instead of our specular highlights being added to the scene, they are subtracted from it. Those parts of our ball that are illuminated by the diffuse elements are unaffected, while the specular "highlight" created by our negative light is subtracted from the result.
One word of warning. If you have plugged any of the specular nodes into the standard specular channel on your object, your negative specular light will create normal positive specular highlights. To combine the specular nodes with negative specular lights, use the Alt_Specular channel.
Finally, negative lights don't need to be just black or white. Here we have created a normal negative light, but set the Specular colour to blue. Figure Seven shows the result of this. Instead of completely removing part of the highlight created by the normal light, our negative light has only removed the blue elements, leaving us with a yellow edge to the highlight.