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Global Ilumination
- overview for newbies-

by PiledotNET
Website: RedPixel.com.br

Hi guys! My name is Filipe M. Deschamps, I'm in charge of Redpixel's 3ds max section and I'm here translating one of my tutorials for our friends at 3D Kingdom (site you're on)!

A lot of people start playing with GI but doesn't realize from where it comes and how it works in real life. Illumination is a decisive factor for a good render, that's why you must study this kind of thing since the theory.

First of all, GI its the abbreviation of Global Ilumination.

*Try to be as much observer as possible, try to note every detail in the image, how the light is transmited, reflected between objects, how shadows are created, etc.

See this two pictures of a sunny day:

Check the strong, more linear shadows and the weak and more fuzy ones that we are going to call as hard shadows and soft shadows, respectively.

Check again how colors and ilumination are reflected between objects. Objects reflect partly the ilumination they recive and this ilumination is visible in the face of the objects around it. Color bleed is the name of this effect. Now see this picture in a cloudy day:

We can see almost the same properties, but not in the same intensity, hard shadows now are gone. This is happening because an general lighting is been casted from the sky, and we can call this a sky light. One of the characteristic of the sky light is produce an illumination coming from all the directions. A cloudy day is exactly that.See the comparison below:

* At left a sunny day. This means one principal point of light (the sun), it will cast light in one direction only creating hard shadows. Remember that the specular highlight is more definite too.

*At right a cloudy day, there is no principal point of light. All sky area is casting light to the objects. This will create shadows too, but shadows in all directions. Since there's light from the right, a shadow will be casted at left; but there's light from left too, so a shadow will be casted at right, same way to all other directions. Note the specular hightlight is unfocused.

Another important factor is the reflection propertie of the light. This implies in exchange of colors between objects (color bleed). Imagine a blue ball next to a white wall. Try to imagine what will happen to the color of the white wall. Execly, it will get a little blue.

The wall stay with this colour because a portion of rays had "collided" with the ball and than with the wall and than been absorved by our eyes. This is what we have to simulate in a 3d scene.

See down two renderings, at left one without GI and the other with GI activated.

From now on, you need to become more observer, watch carefully every thing around you. When you go to the street, whatch how lights and shadows are.. How many lights do you have in your bedroom? How many shadows are been casted from them? Are they hard or softshadows?

Hope this help beginner users that are starting now and intermediate users that skiped this part. :)

This tutorial was written and translated on English by 3D Kingdom knight PiledotNET (RedPixel.com.br)