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Compututer Graphics - Color Modeling And Rendering
This document discusses various color models and rendering techniques. It describes additive and subtractive color models, including the RGB, CMY, and HSV color models. It also discusses illumination models, including ambient light, diffuse reflection, and specular reflection. Common rendering techniques like Gouraud shading and Phong shading are summarized, which interpolate lighting across triangle surfaces. Ray tracing is also briefly explained as a technique for simulating light paths.
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Compututer Graphics - Color Modeling And Rendering
- 1. UNIT - 4 COLORMODEL & RENDERING Prince Soni
- 2. What is thecolor? • Color is a sensation produced by the human eye and nervous system. • Color is the aspect of things that is caused by differing qualities of light being reflected or emitted by them. - It is related to light, but an understanding of the properties of light is not sufficient to understand color, and is especially not sufficient to understand the art of color reproduction.
- 3. Color Model • Acolor model is an orderly system for creating a whole range of colors from a small set of primary colors. • The range of colors that can be described by combinations of other colors is called a Color Gamut. • Color model is of 2 types:- * Additive * Subtractive
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- 5. Color model forRaster Graphics • Hardware Oriented models RGB color model CMY color model YIQ color model • User Oriented model HSV color model
- 6. RGB Color Model: *Additive color model. * For computer displays. * Uses light to display color. * Colors result from transmitted light. * Red + Green + Blue = White.
- 8. * Subtractive colormodel. * Used in ink-jet plotters that deposit pigment on paper. * Uses ink to display color. * Colors result from reflected light. * K for Black * Cyan + Magenta + Yellow = Black. 8 CMY(K) Color Model:
- 9. • Cyan, magenta,and yellow are complements of red, green, and blue. • We can convert RGB into CMY representation by C = 1 - R M = 1 - G Y= 1 - B • Conversion from CMY into RGB R = 1 - C G = 1 - M B = 1 - Y
- 10. YIQ color model •Y => Luminous or Brightness information. • I => Hue (The degree to which a stimulus can be described as similar to or different from stimuli ). For eg. Rust = root color or hue is orange Navy = root color or hue is blue • Q => Purity (Intensity of hue)
- 11. • Y parameter Thecombination of Red, Green & Blue intensities are chosen for Y parameter to give standard luminously curve. Since Y contains luminous information, black and white television monitors use only Y signal. It occupies about 4 MHz bandwidth.
- 12. • I parameter Itcontains Orange, Cyan hue information that provides the Flesh tone shading (use color range to pull darker flesh from the shadows of images) It occupies the a bandwidth of approximately 1.5 MHz. • Q parameter It contains Green, Magenta hue information. It occupies about 0.6 MHz bandwidth.
- 13. • RGB signalcan be converted to television signal using NTSC encoder which converts RGB values to YIQ values, then modulate and superimpose the I and Q information on the Y signal. • Conversion form RGB values to YIQ using following transformation:- Y 0.299 0.587 0.144 R I = 0.596 - 0.275 -0.321 . G Q 0.212 - 0.528 0.311 B
- 14. • NTSC videosignal can be converted to RGB signal using NTSC decoder, which separates the video signal into YIQ components, then converts to RGB using inverse matrix transformation :- R 1.000 0.956 0.620 Y G = 1.000 -0.272 -0.647 . I B 1.000 -1.108 1.705 Q
- 15. HSV color model •The hue (H) of a color refers to which pure color it resembles. All tints, tones and shades of red have the same hue. • Hues are described by a number that specifies the position of the corresponding pure color on the color wheel, as a fraction between 0 and 1. Value 0 refers to red; 1/6 is yellow; 1/3 is green; and so forth around the color wheel. • The saturation (S) of a color describes how white the color is. A pure red is fully saturated, with a saturation of 1; tints of red have saturations less than 1; and white has a saturation of 0. • The value (V) of a color, also called its lightness, describes how dark the color is. A value of 0 is black, with increasing lightness moving away from black.
- 16. Single-Hexcone model ofcolor space
- 17. • The outeredge of the top of the cone is the color wheel, with all the pure colors. The H parameter describes the angle around the wheel. • The S (saturation) is zero for any color on the axis of the cone; the center of the top circle is white. An increase in the value of S corresponds to a movement away from the axis. • The V (value or lightness) is zero for black. An increase in the value of V corresponds to a movement away from black and toward the top of the cone.
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- 19. • How doyou make something look 3D? • Shading that is appropriate for the lighting and the primary cue for 3D appearance.
- 20. Light • Light energyfalling on a surface can be: Absorbed Reflected Transmitted They make an object visible • The amount of energy absorbed, transmitted or deflected depends on the wavelength or intensity of the light.
- 21. • The charactersticsof the light reflected or transmitted depends on: * The surface orientation * The surface properties of the object * Composition of the light source * Direction of the light source * Geometry of the light source
- 22. Illumination model • Illuminationmodel is used to calculate the intensity of the light that we should see at a given point on the surface of the object. • It is also known as Lighting model or Shading model. There are 2 types of illumination model:- (1) Local illumination model:- Direct illumination of surface by light sources. (2) Global illumination model:- All light or surface interactions for entire environment.
- 23. • A commonsimple illumination model is built from 3 components:- * Ambient light * Diffuse reflections * Specular reflection
- 24. Ambient light • Uniformfrom all directions (an object is illuminated uniformly). • Not dependent on light, view or object direction, nor distance to anything else. • La = Ka * Ia • Where, La is a reflected ambient light . Ka is an ambient coefficient. Ia is an ambient light.
- 26. Diffuse Reflection • Diffusereflections consider Point lights (Radiates equal intensity in all direction ) which comes from one direction to generate shading properties a change in color intensity across the surface of an object in relation to light sources. • Depends on direction of light (L) and surface normal (N) Id = Ip(L.N) where, Ip is intensity of point light •
- 28. Specular reflection • Componentof reflection due to mirror-like reflection off shiny surface. • Depends on perfect reflection direction, viewer direction, and surface normal Is = Ip(R.V)^ n where n is Specular exponent, determining falloff rate. • Shininess
- 30. Gouraud shading • Gouraudshading, developed by Henri Gouraud in 1971, was one of the first shading techniques developed in computer graphics. • Gouraud shading is most often used to achieve continuous lighting on triangle surfaces by computing the lighting at the corners of each triangle and linearly interpolating the resulting colors for each pixel covered by the triangle. • Gouraud shading - Wikipedia, the free encyclopedia.htm
- 31. Phong Shading • Itdescribes the way a surface reflects light as a combination of the Diffuse reflection of rough surfaces with the Specular reflection of shiny surfaces .
- 33. Ray tracing • Itis a technique for generating an image by tracing the path of light through pixels in an image plane and simulating the effects of its encounters with virtual objects.