Rough Guide to the Atmopshere Editor – Part 3 – Lighting Models

This is a rather open ended section of the guide as it would take me literally forever to create examples of EVERY lighting model for every different type, so for the purposes of this section I will stick with the default atmopshere with spectral model being used. A basic scene has been produced with a cube with the default texture and a green “plastic” cone. All renders are done at 800×600 in “Broadcast” preset.

As an example of how long it takes to render in each of the lighting schemes a basic grass scene will be used, the atmosphere preset is “default”.

Standard

There are limited settings that can be altered within the standard lighting scheme, in this scheme the light, which will be covered in more detail in part 4, the light comes directly from the sky and hits a surface. As the manual describes…

the light coming from the environment is approximated to a constant term known as Ambient light

This lighting model does not look sepcially realistic and has very few of the sublties that the more advanced models have, below is the scene rendered in the standard model.

Although it lacks realism, the scene renders quickly, this example took 7 seconds. No pre-render is used.

The following scene took 2 mins 49 seconds to render in the standard lighting scheme.

Global Ambience

Global Ambience is a more advanced system than the standard lighting model…

slightly more elaborate estimation of the light coming from the environment: this model takes into account the color of the sky in all directions

It takes light from the sky and radiates it from the surfaces of the objects, i.e. blue sky = blue radiation. However it will not reflect surfaces from objects that are nearby as shown in the image below.

This lighting scheme does not require a pre-render.

The following scene took 2 mins 30 seconds to render in the Global Ambience lighting scheme.

You will notice that although this picture took less time than the standard model, it actually looks more realistic. This is becuase it is reacting more like we anticipate grass should react to light from the sky, whereas in the standard model it pretty much just reacts like a light on paper.

There are various settings which can be explored with Global Ambience they are generic to a number of other lighting systems and so described at the bottom of the page.

Ambient occlusion

Ambient occlusion is a system of lighting that creates excellent shading on models that have a lot of detail. Ambient occlusion works out where light is occluded by tracing the light from the source to the area and discovering where light is blocked, these areas subsequently have more shading. This is a particularly nice looking for complex models with lots of parts as shown below.

The manual describes AO as…

improved version of global ambience where each point on the sky dome is considered like a little source of light. Rays are traced towards each one of these lights, to see whether a neighboring object is occluding the light or not.

This lighting scheme requires a pre-render. The following scene took 8 mins 59 seconds to render in the Ambient Occlusion lighting scheme.

Range
This is best described by the manual..

When the ambient occlusion model is selected, the ambient occlusion Range parameter becomes available. This controls the maximum distance beyond which objects will not contribute to the occlusion. The bigger this value, the closer you get to the Global illumination model and the slower the render. The smaller the value, the closer you get to global ambience (and the quicker the render)

Bruno Memain describes this as:

Range means the distance between one object and the next. If 2 objects sit at 3 meters distance from one another, and the range specified in AO is 2 meters, then those 2 objects won’t cast “local” shadows on each other. If the range is 4 meters, then they will cast ambient shadows on each other. Think of it as a radius around each object. If 2 or more objects are inside this radius, they will cast ambient shadows on each other. But this radius exists for every object in the scene. Object1 will cast sahdows on object2, and if object3 is withinn object2’s radius, it will receive object2 shadows. And if object 4 is in object3’s radius, then, etc, etc.
Also, if object 4 is within object1’s radius, they will also create local shadows onto each other. Now if object1 and object4 are 4 meters distant from one another, there is no point in computing their respective shadow contribution, because in the real world, those 2 objects would not cast ambient shadows onto each other. Hence the range feature.

Global Illumination

A more advanced version of raytracing than ambient occlusion, but working in a similar fashion.

improves over the ambient occlusion model by tracing light rays all the way to the sky dome, thus ensuring that any object will cast ambient shadows onto other objects, whatever the distance.

Obviously greater levels or raytracing will create a much nicer looking light model, but will cause a lot more time to be consumed when renders are taking place.

This lighting scheme requires a pre-render. The following scene took 9 mins 5 seconds to render in the Global Illumination lighting scheme.

Global radiosity

Global radiosity is the most complex lighting systems availiable. Light rays are reflected as they would be to the normal eye, i.e. the light coming from the sun hits the cone, bounces off the cone and then onto the box and subsequently into the eye. The vue manual describes GR as…

the ultimate model in terms of quality of illumination and realism. It propagates light in the scene, instead of propagating shadows as the ambient occlusion and global illumination models do. With this model, objects that are exposed to light will reemit some of that light in all directions, according to the optical properties of their surface. Light will thus “bounce around” repeatedly in the scene, as it would in reality. As a result, each point in the scene receives light from all the other objects in the scene

For a good description of Radiosity and how it affects textures I recommend reading “Texturing Concepts and Techniques” by Dennis Summers, although this book primarily focuses on 3ds max, lightwave and maya there is a lot of good theory behind lighting and texturing.

In the image above you can see that the light radiating from the green cone is transferred onto the default box, this is an effect of radiosity.

GR takes a lot longer to render than the the other lighting schemes as its much more complex to calculate, this scene is not very complex, but in a scene with a lot of objects, trees etc the time taken to render increases dramatically, however it is my opinion that if you have the time it is worth doing as the results are much more believable. This lighting scheme requires a pre-render.

The following scene took 11 mins 59 seconds to render in the Global Radiosity lighting scheme.

Indirect Skylighting
Described by the manual as…

Vue will evaluate the amount of skylight that is received by each object and cast back onto the other objects in the scene. If this option is not selected, the Ambient light color will be used instead of computing the indirect contribution of the skylight. Evaluating the indirect lighting caused by skylight is a slow process. Using the ambient color instead usually yields good enough results.

With Indirect Sylighting On

With Indirect Skylighting Off

Otpimize for outdoor Rendering
This option alters the radiosity levels for indoor and outdoor rendering which according to the manual have different levels due to light dispersal outside.

On

Off

Gain
Gain changes the amount of radiosity of the materials and can create some quite cool effects at greater levels, it is scalar from -1 to 10. The greater the level of the gain, the brighter the materials appear and therefore the more effect the radiosity has, the lower it is, the less effect it will have and threfore the less you will see on the other items.

-1

-0.5

0

1

2

4

6

8

10

Artur Rosa adds:

The radiosity gain and the sky dome lighting gain are normally tightly linked when adjusting the light in a scene. If you change one, typically you have to change the other, keeping (or trying to find) a balance.

Bias
Bias appears to be fairly similar to overall skylight colour except that it works with shadows rather than light.

this color will be added to the light that objects receive from their environment. For instance, if you add a slightly red color, the shadows and light will take a very slight reddish tone. This setting should only be used for very fine tuning of the effects of radiosity.

With Red Bias

With Green Bias

Artur Rosa adds:

The bias color can be used with shades of gray and can be a great contribution to help spread the light in closed environments with few light sources (e.g, a room with sunshine through one window as only light source)

This will be tested/proven shortly.

Bruno Memain adds:

changing the black colour to a lighter grey spreads light more indeed, but it gets very even, and shadows start to dissapear quickly, so keep it in the very dark greys.

This will be tested/proven shortly.

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There are a number of options that can be altered when using many of the lighting systems mentioned above. In order to avoid repetition they will be mentioned together below.

Shadow smoothing
This is an option for the smoothness of the shadows created by the light and is availiable in nearly all the models apart from standard. It is scalar from 0 to 100%, the following examples are created in global radiosity.

0%

25%

50%

75%

100%

Bruno Memain adds:

Shadow smoothing is very misleading term, because it doesn’t smooth out sahdows, but it blurs the noise and blotchiness that is inherent to the radiosity computation. Radiosity creates noise, that’s a fact, and this parameter blurs the moise so it becomes less and less visible, this is just a trick, as opposed to unbiased renderers that keep refining the radiosity solution fror as long as you let it

Artificial Ambience
Artificial ambience is used with global illumination and ambient occlusion as a method of creating ambient light reflections that occur from the sky. It is on a scale of 0 to 1.

0.00 GI

0.20 GI

0.40 GI

0.60 GI

0.80 GI

1.00 GI

0.00 AO

0.20 AO

0.40 AO

0.60 AO

0.80 AO

1.00 AO

Although the effects appear fairly limited, you should be able to see that the textures are gradually getting lighter with greater values. You will also notice greater reflections from the proximate materials on the Ambient occlusion type.

Sky dome lighting gain
This is a setting that moves from -1 to +100 and controls the intensity of the light coming from the sky. Since Global ambience relies on light from the sky the changes ought to be noticeable relatively easily.

-1

-.5

0

5

10

20

100

As you can see, the highlights in the scene begin to dissapear on the sphere and the cube as the scene becomes lighter and lighter.

Overall Skylight Colour
The overall skylight colour determines the colour that the sky has, the default for the scene is a tealish blue (65,99,125) and gives a sky result as follows.

Changing the sky colour to a bright red (255,0,0) changes nothing in the actual sky itself, but changes the colour of light that is shown as bouncing off the objects.

Artur Rosa adds:

the sky dome lighting gain is particularly relevant when the light balance is high. If, for example, you have light balance to 90%, then you’d need to increase the sky dome lighting gain in order to make the shadows “richer” (otherwise they may get too dark).

Quality Boost
The quality boost of the lighting scheme increses the quality of the lighting (rocket science…). The images below show the difference in the quality of the same scene based on global radiosity and states the time taken for each render.

-4 – 10 seconds

-3 – 11 seconds

-2 – 11 seconds

-1 – 11 seconds

0

1 – 15 seconds

2 – 19 seconds

3 – 22 seconds

4 – 26 seconds

Artur Rosa adds:

Low levels of quality boost make blotchy shadows, as you demonstrated, but the blotches decrease as you increase the light balance. In other words, if you have a high light balance you can decrease the quality boost more (and therefore have significant gains in render time).

A big leap between lowest to highest is already noticeable, and the quality of the light has absolutley increased. To test this further the images below are rendered on -4 and +4 with GR to demonstrate a more extreme difference

-4 – 3 minutes 11 seconds.

+4 – 2 hours 21 minutes 16 seconds

Hope this helps, part four is ready