14-光照模型

it tends to produce too much intensity variation for objects close to the light source, and very little variation when d1 is very large. No infinitesimal points.
Vobj α Vlight
θ1
4 Directional Light Sources and Spotlight Effects
Vobj.Vlight=cosα If cosα>=cosθ1 , then the object is with the spotlight(聚光灯). 舞台上的灯光
5 Angular Intensity Attenuation
The coefficient can be adjusted to produce optimal attenuation effects.
We can’t apply the intensity-attenuation calculation equation above to infinitely distant light source, because
Color, position Vector direction and angular limit θ1, as follows:
4 Directional Light Sources and Spotlight Effects
探照灯，汽车灯
Vlight
θ1
4 Directional Light Sources and Spotlight Effects 3
the distance can’t be determined Nearly equal distance.
3 Radial Intensity Attenuation
We use the following intensity-attenuation function for remote and local point source:
3
Photorealism(现实主义, 超级现实主义:
Accurate representations of surface properties Good physical descriptions of the lighting effects in a scene.
Lighting effects:
4
To reduce computations:
Use empirical models based on simplified photometric calculations in most packages More accurate model, such as radiosity algorithm, compute the light intensity by considering the propagation of radiant energy between the light sources and the various surface.
Start:
First: take a look at the basic lighting models often used in computer-graphics system. Then, discuss more accurate, but more complex methods.
10.1 Light Sources
Overview
Realistic display of a scene obtained by
1
Perspective projections to eliminate non-visible surfaces. Applying natural lighting effects.
Illumination model(lighting model,also shading model):
3 Radial Intensity Attenuation
Radiant energy’s amplitude at any distance d1 from the light source is attenuated by the factor 1/d12 So, a surface closer to the light source receives a higher light intensity than the more distant surface with the same properties.
1 fl,radatten= 1/(a0+a1d1+a2d12) ,if source is local ,if source is at infinity
4 Directional Light Sources and Spotlight Effects
A local light source can easily modified to produce a directional, or spotlight beam of light. If an object is outside the directional limits of the light, no illumination. Model such directional light source
3 Radial Intensity Attenuation
In practice, using the above attenuation factor with a point source does not always produce realistic pictures because :
To calculate the color of an illuminated position on the surface of an object.
2
A surface-rendering methods uses the color calculations from an illumination model to determine the pixel colors for all projected positions in a scene. Illumination model can be applied to:
A light source can be defined with a number of properties: Position Color of the emitted light The emission direction It’s shape In real application, a simple light-source model is used to avoid excessive computations RGB is used to represent light-emitting properties and Color parameters and light-source models are discussed in greater detail in next chapter.
Light reflections Transparency Surface texture Shadows
Modeling lighting effects is complex: physical and psychological Here, Illumination models are often approximations of the physical laws that describe surface-lighting effects
Main Topics 2
10.10 Polygon Rendering Methods 10.11 Ray-Tracing Methods 10.12 Radiosity Lighting Model 10.13 Environment Mapping 10.14 Photon Mapping 10.15 Adding Surface Detail 10.16 Modeling Surface Detail with Polygons 10.17 Texture Mapping 10.18 Bump Mapping 10.19 Frame Mapping 10.20 OpenGL Illumination and SurfaceRendering Functions 10.21 OpenGL Texture Functions 10.22 Summary
Every projection position Interpolating colors on the surface, such as scan-line, image-space algorithms.
To avoid misinterpretation:
Illumination model (lighting model): calculate the light intensity at a single surface point. Surface rendering: obtain pixel colors for all projected surface positions.
3 Radial Intensity Attenuation
To generate more realistic displays using point sources, we use the following inverse quadratic function fradatten(d1)=1/(a0+a1d1+a2d12)
1 Point Light Sourc color specified with RGB. Define a point source by: