How to easily convert the gain values in LuxRender to Reality

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How to easily convert the gain values in LuxRender to Reality

Postby Kimberly58 » Sat Mar 12, 2016 10:19 am


As Reality users, we are all used (spoiled?) to the fact that we can change the light intensity of each light while rendering.

LuxRender actually doesn’t adjust the intensity (gain) of each light. What it does is to increase or decrease the intensity of a group of lights. Each light, in Reality, is associated with a group. If you give a different name to each light, then you will be able to adjust each light individually inside LuxRender. But the program is actually acting on a group of lights. This is an important distinction to keep in mind.

Let’s assume that we have a scene with three lights in it. We call those lightsLight-A, Light-B and Light-C. Let’s assume that Light-A and Light–B are assigned to group Front. The other light is assigned to a group called Top. Let’s also assume that Light-A has been given a gain, in Reality, of 0.5, or half intensity. Light-B has been given as an intensity of 0.7 (70% of normal intensity). Light-C has been given an intensity of 1.5.

Whenever we render, we end up with setting the gain for the group calledFront to 1.25. The group called Top has been adjusted to have a gain of 0.8. Now our lighting is perfect as we want. The problem is, the scene is not finished, and we will need to do some more testing renders before we’re done with it. Obviously, we don’t want to repeat those of light adjustments every time we render. Ideally, we would be able to instruct Reality to use those values. So, how can we do that?

The simple solution is to remember that the gain of value in LuxRender is a multiplier for the gain in Reality. Let’s see how it works.

We will start with the lights in group Front. That group was adjusted in LuxRender to a gain of 1.25. That means that we will have to multiply each light in that group by 1.25. So, Light-A had an original volume of 0.5, times 1.25 it gives us 0.625. That will be there body of that we have to enter in Reality. Light-B had an original value 0.7. Multiply that value by 1.25 and we get 0.875. So we set Light-B to have a gain of that value in Reality.

Finally, Light-C was set to 1.5, but the group that it belong to, Top, had its gain adjusted to 0.8. So we multiply 1.5 by 0.8 and obtain 1.2. Let’s set the gain for Light-C in Reality to 1.2 and we are all set. From now on, whenever we render this scene we will get exactly the same lighting without having to adjust anything in LuxRender anymore.

Hope this was useful, see you next time.

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