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Faking Global Illumination
Faking Global Illumination
poorhousefx, updated 2006-10-01 18:31:05 UTC 123,981 views  Rating:
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Faking Global Illumination with point lights

This handout will explain how to use point lights to light a scene and give it the same look as using global illumination. The overall quality is similar, it is easier to do, and best of all, it renders faster. I used a night time kitchen scene from a short film I am working on to create this handout. The final image is shown below (Fig. 1).

click for larger version

The above image is not finalized yet. There are still some things I need to work out such as the hotspots in the ceiling and certain shadows, but this will give you a good idea as to what lighting a scene using this method can do for you.

Now we can get into how this is done. First, let me say that I learned this method from an excellent book I have; Maya 5 Killer Tips. If you have the money, I suggest you buy it. Anyways, let�s start lighting.

The first thing we need to do before we even start with the lights is set the render globals. Open the render global window and set the following (Fig. 2).

1. Set the size for your render under resolution.

2. Then, the most important right now, uncheck Enable Default Lights under the render options tab. We want to do this so we don�t have any extra lights.

3. Under the Maya software tab, change the quality to production quality.

Fig. 2

Now that you have set all of those options, go to your perspective view and go to View > Camera Settings > Resolution Gate (Fig. 3). You will then see a green box which will allow you to frame your render (Fig.4).

Fig. 3

Fig. 4

Once your render view is set I suggest creating a new camera to work with. This way you don�t change you set view. Just go to Create > Cameras > Camera. This will give you another camera called camera1 listed under the panels > perspective in each of your four views. I use this new camera to place lights and look at objects this way my render view I set is not changed on me.

Now we can start adding lights. Like I said, we are going to use nothing but point lights to do this. Then at the end you can add spot lights or whatever light you want for effect. This is how the lights will be set up.

* You will have rows of lights from floor to ceiling and from wall to wall.
* I suggest only using three - four rows of lights for the scene. A left side, right side, and middle.
* Also, keep the lights away from walls and objects or else you will get hotspots.
* Don�t be surprised if you have 40 lights.
* Point lights cast shadows in 6 directions so we will control the direction of the shadows to simulate the look of one light source.
* We will use a low intensity and a cubic decay so the lights die out fast but as a whole illuminate the entire scene.

To start, create a point light, position it, and go to its attributes and set the following. (Fig 5 � 6)

1. The book suggests having all lights have a total intensity equivalent to one. That did not work well for me so I set all my lights intensities to 1. This will vary from scene to scene.

2. Set your decay rate to cubic. This will make the light die out almost instantly.

click for larger version
Fig. 5

1. Now go to shadows and turn on depth map shadows.

2. Now scoll to the bottom of the shadow options and you will see use _ Dmap. This is the six directions the light will cast shadows; + and � X, + and � Y, + and � Z. We can set these to control the direction shadows are cast.

I suggest having three rows of lights. My light source is the moon outside the window, so I set the left side lights to cast shadows down and to the left. The right side; down and to the right. The middle; down and forward. This will help simulate one light source.

Since this light is one the left I told it to cast shadows using the +X axis and �Z axis (down and to the left).

click for larger version
Fig. 6

Now, normally when you add a light you test render it to see the resulting effect. In this situation we will not render until all lights are added. Because the decay rate is set to cubic, even 10 lights will have little to no effect on the scene. Now, take the point light you created and duplicate it 5 more times and move it so it is set like figure 7 below.

Fig. 7

This will act as a base light set up. Right now I duplicated the left side lights so all the lights are casting shadows down and to the left. So now we need to change each row of lights appropriately. So, go light by light and change the shadow direction to the following (Fig. 8)

Fig. 8

The arrows represent the following directions.

* Column 1 = -Y, -Z
* Column 2 = +X, -Z
* Column 3 = +X, -Z
* Column 4 = +Y, -Z

This basically says that column 1 will cast shadows down and to the left. Column 2 and 3 will cast shadows down and forward and column 4 will cast shadows down and to the right. This will simulate one light coming in from behind.

Now all we need to do is duplicate all of the lights and move them forward a little. Then continue to do this until the room is filled (Fig. 9).

NOTE: Remember, you may have to move or delete lights later if they are too close to objects.

Fig. 9

You can see the room is filled with lights. Now we can test render to see the results (Fig. 10)

NOTE: I already added a spotlight outside the window to simulate the moon which is my main light source.

click for larger version
Fig. 10

You can see I marked the flawed areas.

* The red circles show the hotspots which is created by a light being too close to an object. This is fixed by either moving the light away from the object or just simply deleting it.
* The white marks show areas that are too dark. To fix this you can either move some lights you already have, or create a new row of lights to illuminate it.