2. Illumination model, also known as Shading model or Lightning model, is used to
calculate the intensity of light that is reflected at a given point on surface.
There are three factors on which lightning effect depends on
1) Light Source : Light source is the light emitting source.
There are three types of light sources:
a) Point Sources – The source that emit rays in all directions (A bulb in a room).A point
Light is emitted equally in every direction; this why they’re also called omnidirectional
lights. light is fully characterized by its position and its intensity.
3. b) Parallel Sources – Can be considered as a point source which is far from the surface
(The sun).
c) Distributed Sources – Rays originate from a finite area (A tubelight). Their position,
and shape determine the lightning effect.
4. 2. Surface :
When light falls on a surface part of it is reflected and part of it is absorbed. Now the
surface structure decides the amount of reflection and absorption of light. The
position of the surface and positions of all the nearby surfaces also determine the
lightning effect.
3. Observer :
The observer’s position affect the lightning effect.
6. Diffuse reflection : It occurs on the surfaces which are rough or grainy. In this
reflection the brightness of a point depends upon the angle made by the light source
and the surface.
Diffuse reflection is the scattering of light that occurs when it reflects off a surface.
7. - white surface is having its reflexivity close to 1, hence it reflects almost all incoming
light. where as the black surface absorbs most of the incoming light since its reflexivity
is near to 0. so the value of reflexivity is assigned to the range of 0 to 1,depending on
the nature of the surface.
intensity of the diffuse reflection at any point when surface is exposed to
ambient light is given as
I = Kd.Ia
where, Ia = Intensity of ambient light;
Kd = coefficient of reflection;
8. Specular Reflection :
-When light falls on any shiny or glossy surface most of it is reflected back, such
reflection is known as Specular Reflection.
-Specular reflection rarely occurs in nature, but rather in man-made spaces. Still
waters are an example of nature’s ability to produce this type of reflection.
9. The Phong reflection model is an empirical model of the local illumination of points on
a surface.
It describes the way a surface reflects light as a combination of the diffuse reflection of
rough surfaces with the specular reflection of shiny surfaces. The model also includes
an ambient term to account for the small amount of light that is scattered about the
entire scene.
10. Unit 4 : Basics of Lightening
Color Models
1. RGB
2. CMY
3. HSV
11. Color selection
-Selection of color depends on user need,user can select basic colors red,green blue or
different shades of these basic colors
-Color mixing takes place when two or more color come together to form the different
color.
Models for color mixing
1. Subtractive color
2. Additive color
12. Color models
A color model is method of explaining properties or behaviour of color within some
particular context
1. RGB color model
2. CMY color model
13. On color monitors, each pixel is actually composed of three dots -- a red,
a blue, and a green one. A sketch of a pixel showing the red, green and
blue . We can generate 1,67,77,216 colors by controlling intensity of these
pixels
Cyan, Magenta, and Yellow: Combinations of Two Colors
Cyan, magenta, and yellow are mixtures of two of the primary colors with equal intensities of
each.
The colors cyan (light blue), magenta, and yellow with a pixel from each.
14. RGB: -
Stands for "Red Green Blue." RGB refers to three hues of light that can be
mixed together to create different colors. Combining red, green, and blue
light is the standard method of producing color images on screens, such as
TVs, computer monitors, and smartphone screens.
-The RGB color model is an "additive" model. When 100% of each color is
mixed together, it creates white light. When 0% of each color is
combined, no light is generated, creating black.
15. RGB color model : The RGB color model is one of the most widely used color
representation method in computer graphics. It use a color coordinate system with three
primary colors: R(red), G(green), B(blue) Each primary color can take an intensity value
ranging from 0(lowest) to 1(highest). Example: (0, 0, 0) for black, (1, 1, 1) for white,
(1, 1, 0) for yellow
16. CMY color model: In CMY model, we begin with white and take away the appropriate
primary components to yield a desired color.Example: If we subtract red from white,
what remains consists of green and blue which is cyan. The coordinate system of CMY
model use the three primaries’ complementary colors: C(cyan), M(magenta) and
Y(yellow)
17. The corner of the CMY color cube that is at (0, 0, 0) corresponds to white, whereas the
corner of the cube that is at (1, 1, 1) represents black.
Applications of color
1.color has been used to create feelings of coziness
2.Color can affect mood
3. Use in marketing
4.Specific color meaning
5.Attracting attention
6.Individual differences
18. HSV Color Model : HSV stands for Hue, Saturation, and Value (brightness). It is
a hexcone subset of the cylindrical coordinate system. The human eye can see 128
different hues, 130 different saturations and number values between 16 (blue) and 23
(yellow).
19. HLS Color Model : HLS stands for Hue Light Saturation. It is a double hexcone
subset. The maximum saturation of hue is S= 1 and L= 0.5. It is conceptually easy for
people who want to view white as a point.
20. How to Use the HSV Color Model : The HSV color wheel sometimes appears as a
cone or cylinder, but always with these three components:
HUE : Hue is the color portion of the model, expressed as a number from 0 to 360
degrees:
Red falls between 0 and 60 degrees.
Yellow falls between 61 and 120 degrees.
Green falls between 121 and 180 degrees.
Cyan falls between 181 and 240 degrees.
Blue falls between 241 and 300 degrees.
Magenta falls between 301 and 360 degrees.
21. SATURATION
Saturation describes the amount of gray in a particular color, from 0 to 100 percent.
Reducing this component toward zero introduces more gray and produces a faded
effect. Sometimes, saturation appears as a range from 0 to 1, where 0 is gray, and 1 is a
primary color.
VALUE (OR BRIGHTNESS)
Value works in conjunction with saturation and describes the brightness or intensity of
the color, from 0 to 100 percent, where 0 is completely black, and 100 is the brightest
and reveals the most color.
Uses of HSV
-Designers use the HSV color model when selecting colors for paint or ink
-The HSV color wheel also contributes to high-quality graphics. Selecting an HSV color
begins with picking one of the hues and then adjusting the shade & brightness values.
22. HLS Color Model : HLS stands for Hue Light Saturation. It is a double hexcone
subset. The maximum saturation of hue is S= 1 and L= 0.5. It is conceptually easy for
people who want to view white as a point.
-Hue specifies the angle of the color on the RGB color circle, exactly like HSV. -
Saturation controls the purity of the color, exactly like HSV. -
Lightness controls the luminosity of the color.
23. Subtractive color :Subtractive color model explains the mixing of paints dyes,inks
and natural colorants to create full range of colors -
Subtractive color systems start with white light
Additive color : Additive color systems start without light
24. Unit IV Light, Colour, Shading and Hidden Surfaces (07 Hours)
Colour models: Properties of Light, CIE chromaticity Diagram, RGB, HSV, CMY.
Illumination Models: Ambient Light, Diffuse reflection, Specular Reflection, and the
Phong model,Combined diffuse and Specular reflections with multiple light sources,
warn model,
Shading Algorithms: Halftone, Gauraud and Phong Shading.Hidden Surfaces
Introduction, Back face detection and removal, Algorithms: Depth buffer (z), Depth
sorts (Painter), Area subdivision (Warnock)
25. 2. Surface :
When light falls on a surface part of it is reflected and part of it is absorbed. Now the
surface structure decides the amount of reflection and absorption of light. The
position of the surface and positions of all the nearby surfaces also determine the
lightning effect.
3. Observer :
The observer’s position and sensor spectrum sensitivities also affect the lightning
effect.
26. The Effect of Specular Reflection
Specular reflection exerts an effect on our perception of objects. In fact, the beam that
shoots through the specular reflection penetrates the surface it touched by barely half
a wavelength.
However, when a ray of light meets an object, its beams do not all go through the
occurrence of specular reflection at a reflection angle that is equal to the incident
beam.
A counter crafted from a material that reflects a large number of incident beams might
reflect the light source almost perfectly and create a form of blinding ‘spot’ lighting
effect.
27. C.I.E Chromaticity Diagram
● The chromaticity diagram represents the spectral colours and
their mixtures based on the values of the primary
colours(i.e Red, Green, Blue) contained by them.
● Chromaticity contains two parameters i.e, hue and saturation.
When we put hue and saturation together then it is known as
Chrominance.
● Chromaticity diagram represents visible colours using X and Y
as horizontal and vertical axis.
● The various saturated pure spectral colours are represented
along the perimeter of the curve representing the three
primary colours – red, green and blue. Point C marked in
chromaticity diagram represents a particular white light formed
by combining colours having wavelength RED: 700 nm,
GREEN:546.1nm, BLUE:438.8nm
28. C.I.E Chromaticity Diagram
Uses of C.I.E Chromaticity Diagram
● It is used to evaluate a color against a gamut(range).
● It is used to represent all chromaticities visible to the average person.
● It is used to find the range of colors.
● It is used to find dominant and complementary colors.
Advantages:
● Simple geometric construction for mixing two or more colours.
● Both Perceptual attributes used: hue and saturation
