LIGHTING AND ILLUMINATION

Dr. Aree Ali Mohammed Assistant Professor 2014-20153rd Stagearee.ali@univsul.edu.iq

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What is Lighting?

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Example 1. Find the cubic polynomial or that passes through the four points and satisfies

1. As a photon

Metal Insulator

What is Lighting?

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Light plays an important part in computer graphics for rendering realistic images.Using lighting models, we can simulate shading, reflection and refraction of light, comparable to what we see in the real world.

2. As a wave

What is a Illumination?

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Example 1. Find the cubic polynomial or that passes through the four points and satisfies

Interactions between light sources and the object surface

An “illumination model” describes inputs, assumptions, and outputs used to calculate illumination (color / brightness) of surface elements

Usually includesLight attributes (intensity, color, position, direction, shape)Object surface properties (color, reflectivity, transparency, etc.)Interaction between lights and objects

Basic Light Sources

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Example 1. Find the cubic polynomial or that passes through the four points and satisfies

The amount that a light illuminates an object decreases with the square of the distance between them. This is known as Light Attenuation.

As part of illumination models, one can specify whether the light intensity varies with the distance between the object and the light source

Illumination Models

Local Illumination Takes only direct lighting information refers to direct interaction between one light source and one object

surface.

Global Illumination refers to the interaction of light between all surfaces in a scene. Most light striking a surface element comes directly from a light emitting

source (direct illumination) Sometimes light from a source is blocked by another object, resulting in

shadows However, objects in the shadow can still receive light from light bouncing

off other objects (indirect illumination)

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Example 1: Local Illumination

• Only considers the light, the observer position, and the object’s material properties

• OpenGL does this.

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Example 2: Global Illumination

• Takes into account of the interaction of light from all the surfaces in the scene

• Recursive ray tracing is an example. It models light rays bouncing between objects

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Local Illumination Model

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In computer graphics, single object-light interaction is approximated through local illumination models.Basic model used is the Phong model which breaks local illumination into 3 components:

Ambient reflectionDiffuse reflectionSpecular reflection

For every point, or small surface area, of an object, we want to calculate the light due to these three components.

Ambient Reflection

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Example 1. Find the cubic polynomial or that passes through the four points and satisfies

Ambient light = background light, it is used to simulate indirect lighting

• Ambient component• Independent of

Object’s position Viewer’s positionLight source’s position

• Dependent of A constant factor (in each of the R, G, B channels)

Diffuse Reflection• Diffuse light = illumination that a surface receives from a light

source that reflects equally in all directions

• Independent of:• Viewer’s position

• Dependent of:• Light’s position• Surface property (normal, reflectance property)

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Lambert’s Law• Need to know how much light a point on the object receives from the

light source• Solution based on Lambert’s Law

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Point receives more light Point receives less light

Diffuse = Kd*I*cos(theta)

Specular Reflection I

Specular light = light reflection from shiny surfaces Color depends on material and how it scatters light

Shiny surfaces (metal, mirror, etc.) reflect more light Specular light depends on both light source position and

view position

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Example 1. Find the cubic polynomial or that passes through the four points and satisfies

Specular Reflection II

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Example 1. Find the cubic polynomial or that passes through the four points and satisfies

Variation in Diffuse and Specular in Local Model• Putting Diffuse and Specular together in a local

illumination model

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Example 1. Find the cubic polynomial or that passes through the four points and satisfies

Phong Lighting Equation

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Shading vs. Lighting How is Shading different from

Lighting?

Lighting evaluates the lighting equation at each point on the surface of an object

Shading is kind of a “hack” that computes only lighting equations on the vertices, and interpolates the pixels in between