Dissertation fragments part 2
I publish this post to carry on publishing fragments of my Dissertation about shading in Maya:
Light types in Maya surface:
In the real life there is not only one type of light. This changes depending of the issuer (the sun, a lamp, a reflector…). To be able to simulate all this variety in a digital surface, it were created a different types of light that are equal in all 3D software although they are named in different ways depending on each one. In Maya they have the following names: Point Lights, Spot Lights, Directional lights, Ambient Lights, Area Lights and Volume Lights:
– Point Lights: Simulate punctual light rays to infinite directions in a homogeneous way. Light bulbs or other little light generator can be simulated using point lights, although in the real world any light generator is 100% omnidirectional. To do this there are some techniques as decide if they should cast shadows or not.
– Spot Lights: They illuminate a cone shaped area. Spot lights are punctual too but the difference between them and Point lights are that Spot don’t illuminate equally in all directions. The artist can limit the influence area and the softness of the light borders in order to create different sizes and transitions between light and shadows. They are the equivalent of the theatre or automobiles lighting.
– Directional Lights: This kind of lighting is not punctual. Once you use it parallel light beams appear in the direction you choose. In this kind of light you can’t control the proximity of the light issuer, only the direction of the light rays manipulating the rotation controller. It’s used to simulate sunshine ambient or to be part of the secondary lighting in a light set.
- There is a particular direction light no able for Maya Software named Physical Sun and Sky that recreate in a veridical way the Kelvin colour temperature and the different intensities on sun light in lumens during the day. It’s able to reproduce every time of the day only rotating the light controller. If you put it perpendicularly to the ground it will seem to be mid day, but if you put it to 35º to the ground it will seem to be the sunrise.
– Ambient Light: It’s used to illuminate indirectly the different objects of your scenario. Its function is to illuminate the parts where are not illuminated by direct lighting and they appear too dark. Using the ambient light, illumination seems more realistic and there is no lack of information. But, this kind of light has some big troubles. It’s difficult to obtain a good control of it and it hasn’t a nice quality in shading, so it is criticised by the amount of professionals who have searched some better alternatives.
– Area Lights: These are lights underused because of his large rendering time. They are used to project lights and shadows to simulate the light what pass through a window. It has an excellent shading quality but is used only with still images in info architecture.
– Volume Light: This kind of light has the advantage that you can know which volume the light influence has, because the only that will be illuminated is all which is inside of the influence sphere. You can configure if you want a punctual or a directional light, and this is another advantage of the light.
What is a shader?
A shader is a mathematical model that represents the way that light interacts with the surface of the model.
When a light hits a surface there are three different things that happen: Reflectance, Absorption and Transmission.
Reflectance: The light hit the surface and then it bounces away. There are different tipes of reflectance depending on the object’s surface.
– Difuse reflection: If it is rough it produces diffuse reflections. It means that the light hits and its reflections go in so many different directions. As the reflected light goes to all directions, you can see it from any angle equally. The Maya’s material to reproduce diffuse reflection surfaces is Lambert.
– Specular reflection: Perfectly smooth surface reflects the light in the same angle it arrives. The most common example of how specular reflections work is a mirror. If you change the angle of the mirror you change what you see in its surface
– There is a middle ground, when the surface is not smooth enough to act like a mirror, where light is reflected in many directions but some portions of that light are reflected in a specular way. In Maya, to control this middle ground we use as we know as “specular highlight” which helps us controlling what roughness quantity has our material. In Maya, these kinds of surfaces are called Blinn or Phong, which are two different ways to control its roughness.
Absorption: Light is converted into heat, it’s not longer visible light and we can’t see it. Different wavelengths acts different in the same surface, some of them are absorbed or not. This is what creates as we know as colours. If a surface absorbs all wavelengths of a light ray, it will be black and it will be easier to heat. If a surface doesn’t absorb any wavelength it will be white. But, if it absorbs every wavelength but green ones, the surface will be green. So colour is the wavelength of a light ray than a surface can’t absorb. This phenomenon is called Specular Colour, because reflections of non-absorbed wavelengths are specular.
Transmission: Light goes through the surface. There are some different transmission levels. If light can’t pass through we call this surface opaque and if all light rays can do it we call it transparent. In transmission there is a middle ground too, when part of the light can pass. It’s called translucent or semi transparent surface.
When light pass through a surface his environment changes. The atomic composition of a solid material is different than air, so light rays tend to change their direction. It’s called refraction. Depending on the difference between the normal direction and the one through the solid material it will have a different refraction index.
Depending on the qualities of the surface, different light spectres will interact in a different way whit it, and only combining these mathematical models we can do all the material variations we need.
I want to add, that I choose the 5000-word option to defend my thesis.