Basic Illumination Models/ Shading Model/ Lighting Model
These Basic Illumination Models give the simple and fast method for calculating the intensities of light for various reflections.
- This is a simple way to model combination of light reflection from various surfaces to produce a uniform illumination called ambient light, or background light.
- Ambient light has no directional properties. The amount of ambient light incident on all the surfaces and object are constant in all direction.
- Also, If consider that ambient light of intensity 𝐼𝑎 and each surface is illuminated with 𝐼𝑎 intensity then resulting reflected light is constant for all the surfaces.
- When some intensity of light is falling on the object surface and that surface reflects light in all the direction in equal amount then the resulting reflection is called diffuse reflection.
- Ambient light reflection is the approximation of global diffuse lighting effects.
- Diffuse reflections are constant over each surface independent of our viewing direction.
- Amount of reflected light depends on the parameter Kd, the diffuse reflection coefficient or diffuse reflectivity.
- Kd is assigned value in between 0 and 1 depending on reflecting the property. Shiny surface reflects more light so Kd assigned larger value while dull surface assigns small value.
- Moreover, If a surface exposed to only ambient light we calculate ambient diffuse reflection as: 𝐼𝑎𝑚𝑏𝑑𝑖𝑓𝑓 = 𝐾𝑑𝐼𝑎, Where 𝐼𝑎the ambient light falling on the surface.
- Practically most of times each object illuminated by one light source. So now we discuss diffuse reflection intensity for the point source.
- We assume that the diffuse reflection from a source scattered with equal intensity in all directions. Independent of the viewing direction such a surface sometimes referred as the ideal diffuse reflector or Lambertian reflector.
- This model of Lambert’s cosine law. this law states that the radiant energy from any small surface area dA. In any direction ∅𝑛 relative to a surface normal proportional to 𝑐𝑜𝑠∅𝑛.
- Fig of Basic Illumination Models, Radiant energy from a surface area dA in direction Φn relative to the surface normal direction.
- As shown reflected light intensity does not depends on viewing direction so for Lambertian reflection. The intensity of light same in all viewing direction.
- Even though there the equal light distribution in all direction from perfect reflector the brightness of a surface does depend on the orientation of the surface relative to light source.
- As the angle between the surface normal and incidence light direction increases light falls on the surface decreased.
- Moreover, If we denote the angle of incidence between the incoming light and surface normal as then the projected area of a surface patch perpendicular to the light direction proportional to 𝑐𝑜𝑠𝜃.
- If 𝐼𝑙 the intensity of the point light source, then the diffuse reflection equation for a point on the surface can write as 𝐼𝑙,𝑑𝑖𝑓𝑓 = 𝐾𝑑𝐼𝑙𝑐𝑜𝑠𝜃
- Moreover, A surface illuminated by a point source only if the angle of incidence in the range 00 to 900. . Other than this value of the light source behind the surface.