Seminar LIGHTING MODELS What is a light? Types of light - - PowerPoint PPT Presentation

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Seminar LIGHTING MODELS What is a light? Types of light - - PowerPoint PPT Presentation

Feb 11, 2023 368 likes •1.64k views

Computer Graphics Seminar LIGHTING MODELS What is a light? Types of light Illumination models Shading models What is a light? Illumination models Shading models Lighting models What is a light? Delta Lights

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Computer Graphics

Seminar

LIGHTING MODELS

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What is a light? Types of light Illumination models Shading models

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What is a light? Illumination models Shading models Lighting models

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What is a light?

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Delta Lights

Light entities with no physical size Used because simulating area lights was

for a very long time too expensive

today should be avoided as much as

possible

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What is a light? Types of light Illumination models Shading models

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Types of light

Directional light Point light Spotlight

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Directional light

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Point Light

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Point light VS Spotlight

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Spotlight

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What is a light? Types of lights Illumination models Shading models

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Illumination Models

Global Illumination = Ambient Light + Diffuse Light + Specular Light + Emissive Light

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The emissive ligthing

  • Each polygon is self-luminous

(it lights itself, but does not give off light)

  • There are no lights in the scene
  • Each polygon has its own colour which is constant

Over its surface That color is not affected by anything else in the world position of viewer is not important

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Calculating Emissive Term

emissive = Ke

where: Ke is the material's emissive color.

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The Ambient Term

Ambient light does not appear to come from any particular direction, rather it appears to come from all directions, because

  • f this it does not depend on light source position.
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Calculating Ambient Term

ambient = Ka x globalAmbient Where :

Ka is the material's ambient colour

globalAmbient is the color of the incoming ambient light.

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Diffuse Term

comes from a specific direction

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Diffuse Term

The diffuse term accounts for directed light reflected off a surface equally in all directions.

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The Diffuse Term

diffuse = Kd x lightColor x max(N · L, 0) Kd is the material's diffuse color lightColor is the color of the incoming diffuse light N is the normalized surface normal P is the point being shaded.

L is the normalized vector toward the light source

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The Specular Term

Rendering the specular term Light is reflected from the surface in mirror direction brightness depends on theta - angle between surface normal (N) and the direction to the light source

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The specular Term

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Specular Term

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Adding The terms together

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Ambient+Diffuse+Specular

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Material Properties Demo

diffuse color -how the material reflects light diffusely specular color –how material reflects light specularly

http://math.hws.edu/graphicsbook/c4/s1

.html

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Different Lighting Models

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Phong Lighting Model

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Phong Ligthing model

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Blinn-Phong Lighting Model

Another, a bit more realistic, lighting model is the Blinn- Phong model that calculates the specular term somewhat differently.

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Blinn phong VS phong

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real-world photograph

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What is a light? Types of light Illumination models Shading models

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What is shading?

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Shading models

There are three main shading models that are used for different result. Flat Shading Gouraud Shading (per vertex) Phong Shading (per fragment)

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Three main shading models

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3D mesh

Consists of: Vertices, edges that form faces, Face normals - orthogonal to the face. Normals + light source we determine Colour of the face.

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Flat Shading (per polygon)

 It defines a single color for a face.  main idea is that we use only one surface normal per polygon  The color itself is uniform (unchanging) on that polygon.

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Flat shading

is in screen space ⊕ easiest to implement, really fast ⊖ ugly results, only good results if mesh resolution is such that one face corresponds to one pixel on the screen, this breaks down when zooming in.

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Example of Flat Shading Model

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Linear interpolation

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Positive and Negative sides of Gouraud Shading

  • is in screen space

⊕ pretty efficient and not too hard to implement, nice shading on medium to high mesh resolution ⊖ looks bad on low mesh resolution, has perspective distortion, which can also be noticed on rotation of the object or if you change the triangle shapes. ⊖ if the light source is specular and focused on a very small area, Gouraud Shading might not render it correctly (if it doesn’t hit and illuminate a vertex, but only hits a face or an edge of the mesh)

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Example of Gouraud Shading

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Phong shading

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Results of Phong Shading

⊕ great shading of round and smooth objects at any mesh resolution ⊖ can’t change the mesh contour ⊖ is more challenging to implement and takes longer to compute than the other two algorithms ⊖ always assumes a smooth basic shape, i.e. if the object we want to display has sharp edges that should actually be sharp (e.g. if we try to render a cube), it will make the edges look somewhat round instead of shading the faces in different light.

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Example of Phong Shading

http://multivis.net/lecture/phong.html

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If the object resolution is higher

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Fog

Fog makes objects that are further away look less distinct than near objects

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Why is fog shading needed ?

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The monster sees a much softer horizon

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Thank you !

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