lighting and shading in computer graphics

13 jun lighting and shading in computer graphics

Lighting and ShadingLighting and Shading 15-462 Computer Graphics I Lecture 7. University of Freiburg –Computer Science Department –Computer Graphics - 17 Summary light consists of photons irradiance and radiant exitance describe the flux, i.e. So no, they both are not responsible for creating shadows. Lighting and ShadingLighting and Shading 15-462 Computer Graphics I Lecture 7. A light with this property is called a directional light. Flat shading 2. While lighting techniques offer flexibility in the level of detail and functionality available, they also operate at different levels of computational demand and complexity. 75-79 and March 1989, pp.  APIs (D3D, OGL) employ Blinn-Phong lighting and Gouraud shading. Illumination Models and Shading Page 1 Illumination Models and Shading 1 So Far … Next step… 2 wireframe hidden surfaces What’s Missing ? • Light ! • Need to understand: –How lighting works •Types of lights •Types of surfaces –How shading works •Shading algorithms 3 Lighting vs. Shading Lighting  Uses linear interpolation of normal vectors, rather than colors. Gouraud shading, developed by Henri Gouraud in 1971, was one of the first shading techniques developed in computer graphics. Shading refers to depicting depth perception in 3D models or illustrations by varying levels of darkness. Example of flat shading vs. Phong shading interpolation. 21 CS130 : Computer Graphics Lighting and Shading Tamar Shinar Computer Science & Engineering UC Riverside. We start with algorithms for high-quality local illumina-tion using alternative lighting models such as the one by Torrance and Sparrow [39]. This type of lighting is re-created in computer graphics by radiosity techniques, which model light as energy rather than rays and which look at the effects of all the elements in a scene on the appearance of each object. Flat shading is lighting technique normal and the direction of the light source, their respective colors and the intensity of the light source. Lighting model – technique that defines how do we calculate the final color given all the components required for it. 82-89. Lighting and Shading Announcements • Written assignment #1 due Thursday – Handin at beginning of class • Programming assignment #2 out Thursday. Computer Graphics If there is one light and one material, the following things can be set independently: • Global scene ambient red, green, blue • Light position: x, y, z • Light ambient red, green, blue • Light diffuse red, green, blue • Light specular red, green, blue • Material reaction to ambient red, green, blue Gouraud shading was developed by Henri Gouraud and was first published in 1971. Gouraud Shading is an interpolation method used in computer graphics to produce continuous shading of surfaces represented by polygon meshes. If it with a blue light, or a green light, or an aqua light it will appear black (as those lights have no red component.) “Lighting” Two components: Lighting Model or Shading Model - how we calculate the intensity at a point on the surface Surface Rendering Method - How we calculate the intensity at each pixel Jargon Illumination - the transport of light from a source to a point via direct and indirect paths Lighting - computing the luminous intensity for a specified 3D point, given a viewpoint Shading … In a typical computer graphics model, the incident light is modeled as an RGB color, and the material of the surface is also modeled as an RGB color. Computer graphics lighting is the collection of techniques used to simulate light in computer graphics scenes. Department of Computer Sciences Graphics – Spring2013 (Lecture 14) Relevant Vectors for Phong Shading n l θ α v r θ The shading of a point on a surface is a function of the relationship between the viewer, light Lighting and Shading A. Shading Language Details Vector Components. Directional lights do not exist in reality, but in computer graphics, it is often worthwhile to identify situations in which a directional light is sufficient. Phong shading more work than Gouraud shading Move lighting calculation to fragment shaders Just set up vectors (l,n,v,h) in vertex shader • Set Vectors (l,n,v,h) • Calculate vertex colors • Read/set fragment color • (Already interpolated) Hardware Interpolates Vertex color a. Gouraud Shading • Set Vectors (l,n,v,h) For N lights, repeat calculation for each light In practice, Gouraud shading is used to achieve smooth lighting on low-polygon surfaces without the heavy computational requirements of calculating lighting for each pixel. quality of shading and lighting in hardware-accelerated computer graphics. Shading tries to approximate local behavior of light on the object's surface and is not to be confused with techniques of adding shadows, such as shadow mapping or shadow volumes, which fall under global behavior of light. In simplified terms, shading controls how object's surface's brightness changes when the angle between its normal and light vector changes. If this red polygon is hit with a white light it will appear red. Question 43 : A shading Model: Option-1 : is used to calculate the intensity of light that we should see at a given point on the surface of an object Option-2 : uses the intensity calculations to determine the light intensity Option-3 : scattered light from a rough surface Option-4 : light … The title of this chapter is “Shading,” not “Illumination”; these are two different but closely related concepts. Compared to light calculations, where we can have some (often quite a lot) deviation from reality, for shadows it is more easily detectable if something is wrong. The lighting model is based on three simple components of light that model indirect, direct, and reflective Lighting and Shading Learn to shade objects so their images appear three- dimensional Introduce the types of light -material interactions Build a simple reflection model ---the Phong model--- that can be used with real time graphics hardware Work on fragment shaders for different types of lighting References I Foley,Chapter16(Illuminationandshading),upto16.3 I Shirley,Chapter10(Surfaceshading) Title: Computer Graphics 5 - Illumination and Shading Phong Shading Phong shading is not what earlier graphics hardware implemented. 02/04/2003 15-462 Graphics I 2 Remarks About Assignment 2Remarks About Assignment 2 • Remember that object transformations are applied in the reverse order in which they appear in the code! James F. Blinn, "What We Need Around Here is More Aliasing", and "The Return of the Jaggies", IEEE Computer Graphics and Applications, January 1989, pp. Illumination refers to the math and algorithms necessary to compute the effect of light on a single point in the scene; shading deals with techniques that extend the effect of light on a discrete set of points to entire objects. Shading Techniques • Constant Shading – Calculate one lighting calculation (pick a vertex) per triangle – Color the entire triangle the same color • Gouraud Shading – Calculate three lighting calculations (the vertices) per triangle – Linearly interpolate the colors as you scan convert • Phong Shading – While you scan convert, linearly interpolate the normals. Lighting I Phongilluminationmodel Shading I Flatshading I Gouraudshading I Phongshading. Shading is what gives the objects their three-dimensional appearance Without shading, the surfaces look flat An orthographic projection of a sphere appears as a circle An orthographic projection of a cube (from (1, 1, 1) appears as a hexagon Graphics artists can choose from a variety of light sources, models, shading techniques, and effects to suit the needs of each application. In practice, Gouraud shading is most often used to achieve continuous lighting on triangle surfaces by computing the light […] The disadvantage of flat shading is that it gives low-polygon models a faceted look. – local illumination, light directly emitted by light sources – global illumination , light reflected from and transmitted through its own and other surfaces •Shading algorithms 3 Lighting vs. Shading Lighting –Interaction between materials and light sources –Physics • Shading Zbuffer –Determining the color of a pixel –Computer graphics • Shading usually determined by lighting (Scene) … putColor (x,y,col P)) … end 4 The Physics Basic Illumination Model We get something like •But we want. LIGHTING AND SHADING 8.1 Point and parallel lights In the real world, all lights have a nite size and shape, and a location in space. Example 5-9. There are a number of techniques that can be used to create shadows for the objects. the number of photons per time, into or from a surface per area radiant intensity is flux into a direction per solid angle It is usually used for high speed rendering where more advanced shading techniques are too computationally expensive.. 37. CAP4730: Computational. Lighting v Shading • lighting: interaction between light and surface (e.g.using Phonglighting model; think about this as “what formula is being used to calculate intensity/color”) • shading: how to compute color of each fragment (e.g.what attributes to interpolate and where to do the lighting calculation) 1. For example, a brightly coloured object will cast a slight glow of the same colour on surrounding surfaces. Shading in OpenGL Ed Angel Professor of Computer Science, Electrical and Computer Engineering, and Media Arts University of New Mexico The shading model has two primary ingredients: properties of the surface and properties of the illumination falling on it. Specify material properties 4. To yield more realistic shading with intensity varying from point to point on a surface needs due consideration to change of curvature, the direction of incident light and position of viewpoint from one point on a surface to another. The vectors that you send in to your shaders typically represent colours, vertex coordinates, surface normal, and texture coordinates. Slide 1 CSPC 352: Computer Graphics Chapter 6: Lighting and Shading Slide 2 Interactive Computer GraphicsChapter 3 - 2 Overview Local and global illumination Phong reflectance… This approach is based on an analytic factoriza-tion of … using Phong lighting model; think about this as “what formula is being used to calculate intensity/color”) • shading: how to compute color of each fragment (e.g. Shadows are areas where the light cannot reach because it's occluded by other objects. Computer Graphics Simple Shading Models A jumbled collection of ad hoc & heuristic techniques, developed over the past two decades Concerned mostly with the primary ray (light source to surface to viewer) Secondary, tertiary, etc. Shading is referred to as the implementation of the illumination model at the pixel points or polygon surfaces of the graphics objects. Gouraud shading is a method used in computer graphics to simulate the differing effects of light and colour across the surface of an object. Computer Graphics Chapter 6 - Lighting and Shading Overview. Lighting models are used to replicate lighting effects in rendered environments where light is approximated based on the physics of light. Without lighting models, replicating lighting effects as they occur in the natural world would require more processing power than is practical for computer graphics. This Intensity-Interpolation scheme, developed by Gouraud and usually referred to as Gouraud Shading, renders a polygon surface by linear interpolating intensity value across the surface. THE LIGHT SOURCES sources, reflection models and shading model which can be The object is illuminated by light which is to follow rays of applied in computer graphics. Lighting and Shading Outline •Lighting •Lighting models •Ambient •Diffuse •Specular •Surface Rendering Methods •Ray-Tracing What we know • We already know how to render the world from a viewpoint. View ch6.pptx.pdf from EE 170 at University of Engineering and Technology, Peshawar. Enable lighting and select shading model 2. 2 ... –real-time color 3D graphics is feasible –any scheme for describing color requires only three values –lots of different color spaces--related by 3x3 matrix transformations. Specify normals 3. Interpolated Shading is a kind of trade-off between computational expense and realistic shading quality. Specify lights Enable Lighting Calculations Lighting calculations are enabled globally in an OpenGL program using glEnable (GL_LIGHTING); Once lighting is enabled, glColor*() ignored CSPC 352: Computer Graphics Chapter 6: Lighting and Shading Chapter 3 - 2 Interactive Computer Shading model – technique that defines when and where do we calculate the components needed for light calculations. ROCEDURAL shaders are widely used in computer graphics today, as demonstrated by the success of shading languages such as the RenderMan Shading Language [1] and GPU shading languages such as Cg and HLSL [2]. Moreover the examples of those light from light-emitting on the object surfaces called light formulations are also discussed. Procedural shaders provide several advantages over sampled texture maps, including the ability to show lighting that is based on a simple model of the interaction of lights and surfaces, and shading that is based on a simple model of how color changes across a graphics surface primitive. 3 Shading To compute the di usely re Introduction of Shading. 2 Why we need shading •Suppose we build a model of a sphere using many polygons and color each the same color. Backgroundofillumination ... Shading I Gouraudshading I Phongshading. Intensity values for each polygon are coordinate with the value of adjacent polygons along the common edges, thus eliminating the intensity discontinuities that can occur in flat shading. Shading model is used to compute the intensities and colors to display the surface. SHADING Slides modified from Angel book 6e SHADING I 3 COSC4328/5327 Computer GraphicsCOSC4328/5327 Computer Graphics Objectives •Learn to shade objects so their images appear three- dimensional polygons and color it with •Introduce the types of light-material interactions •Build a simple reflection model---the Phong model--- that can be used with real time graphics hardware 1. 02/12/2002 15-462 Graphics I 2 Remarks About Assignment 2Remarks About Assignment 2 • Remember that object transformations are applied in the reverse order in which they appear in the code! r ) + k ab I ab Above equation is just for one light source!! Since the components of these vectors have different meanings, GLSL provides special accessors that you can use to refer to the components. It focuses on two related areas that give improved representations of how images look: lighting that is based on a simple model of the interaction of lights and surfaces, and shading that is based on a simple model of how color changes across a graphics surface primitive. What we know We already know how to render the world from a viewpoint. Shading refers to the depiction of depth perception in 3D models (within the field of 3D computer graphics) or illustrations (in visual art) by varying the level of darkness. This allows you to avoid computations that will not produce perceptible results. Phong shading applies lighting computation per- pixel. Lighting v Shading • lighting: interaction between light and surface (e.g. Structures in Computer Graphics. reflection not considered Shading … If it is hit with a yellow light or a purple light it will appear red (as the polygon will reflect the red component of the light.)

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