Презентация по информатике на тему «Компьютерная графика» (7 класс) Инфоурок › Информатика ›Презентации›Презентация по информатике на тему «Компьютерная графика» (7 класс)

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Компьютерная графика. Подготовила учитель информатики и математики филиппова Ольга Николаевна

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Компьютерная графика – это область информатики, занимающаяся проблемами получения различных изображений ( рисунков, чертежей, мультипликаций) на компьютере.

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Основные области применения компьютерной графики. Научная графика первые компьютеры использовались лишь для решения научных и производственных задач. Чтобы лучше понять полученные результаты, производили их графическую обработку, строили графики, диаграммы , чертежи.

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Деловая графика. Деловая графика — это область компьютерной графики, предназначенная для наглядного представления различных показателей работы учреждений. Плановые показатели, отчетная документация, статистические сводки — это объекты, с помощью которых в деловой графике создаются иллюстративные материалы. Программные средства деловой графики включаются в состав электронных таблиц.

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Конструкторская графика. используется в работе инженеров-конструкторов, архитекторов, изобретателей новой техники. Этот вид компьютерной графики является обязательным элементом САПР (систем автоматизации проектирования). Средствами конструкторской графики можно получать как плоские изображения (проекции, сечения), так и пространственные трехмерные изображения. 

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Иллюстрированная графика. Программные средства иллюстративной графики позволяют человеку использовать компьютер для произвольного рисования, черчения подобно тому, как он это делает на бумаге с помощью карандашей, кисточек, красок, циркулей и других инструментов.

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Художественная и рекламная графика. Художественная и рекламная графика — ставшая популярной во многом благодаря телевидению. С помощью компьютера создаются рекламные ролики, мультфильмы, компьютерные игры, видеоуроки, видеопрезентации. Графические пакеты для этих целей требуют больших ресурсов компьютера по быстродействию и памяти.

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Пиксели. Пиксель представляет собой единицу измерения экрана любого современного монитора, будь то компьютер, ноутбук, мобильный телефон, навигатор и так далее. Другими словами, отвечая на вопрос о том, что такое пиксель, можно ответить, что это просто точка.

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Виды компьютерной графики. Различают три вида компьютерной графики. Это растровая графика, векторная графика и фрактальная графика. Они отличаются принципами формирования изображения при отображении на экране монитора или при печати на бумаге Растровая графика.

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Растровая графика. Растровая графика — это графическое изображение на компьютере или в другом цифровом виде, состоящее из массива сетки пикселей, или точек различных цветов, которые имеют одинаковый размер и форму.

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Векторная графика. Векторная графика – это перечень всех объектов (линий, фигуры и т.д.) из которых состоит векторное изображение,  каждому из объектов в изображение определено, к какому из классов объектов он относится и принадлежит, также приведены определенные параметры  для управления объектом.

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фрактальная графика. Фрактальная графика является на сегодняшний день одним из самых быстро развивающихся и перспективных видов компьютерной графики.  Математической основой фрактальной графики является фрактальная геометрия. Здесь в основу метода построения изображений положен принцип наследования от, так называемых, «родителей» геометрических свойств объектов-наследников. 

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Практическая часть

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Проверь себя! 1. Выполните задания предложенные учителем. 1.Какие виды графики вы знаете? 2. В чем отличия их друг от друга?

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Презентация » Компьютерная графика»

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Компьютерная графика

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Компьютерная графика

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История компьютерной графики

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Компьютерная графика

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Компьютерная графика

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Компьютерная графика

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Компьютерная графика

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Компьютерная графика

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Компьютерная графика

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Компьютерная анимация — это получение движущихся изображений на дисплее. Компьютерная анимация — это получение движущихся изображений на дисплее. Мультимедиа –это объединение высококачественного изображения на экране компьютера со звуковым сопровождением.

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Компьютерная анимация

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Компьютерная графика

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Компьютерная графика

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Трёхмерная графика

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90000 PPT — Computer Graphics PowerPoint Presentation, free download 90001 90002 90003 90004 Computer Graphics 90005 Prof. Muhammad Saeed 90006 90007 90008 90003 90004 Hardware II 90005 Computer Graphics Hardware (Graphic Cards) II 90006 90007 90014 90003 90004 Hardware II 90005 Computer Graphics PCI (Peripheral Component Interface) With a PCI-based graphics card, every texture map has to be stored twice .First, the texture map is loaded from the hard drive to the system memory (RAM) until it has to be used. Once it is needed, it is pulled from memory and sent to the CPU to be processed. Once processed, it is sent through the PCI bus to the graphics card, where it is stored again in the card’s framebuffer. All of this storing and sending between the system and the card is very draining to the overall performance of the computer. 90006 90007 90020 90003 90004 Hardware II 90005 Computer Graphics AGP (Accelerated Graphics Port) Card AGP is built on the idea of ​​improving the ways that PCI transports data to the CPU.Intel achieved this by addressing all of the areas where PCI transfers were causing data bottlenecks in the system. By clearing the traffic jams of data, AGP increases the speed at which machines can render graphics while using the system’s resources more efficiently to reduce overall drag. It achieves the goal by: 90006 90007 90026 90003 90004 Hardware II 90005 Computer Graphics • 1. Dedicated Port • There are no other devices connected to the AGP other than the graphics card.With a dedicated path to the CPU, the graphics card can always operate at the maximum capacity of the connection. • 2. Pipelining • This method of data organization allows the graphics card to receive and respond to multiple packets of data in a single request. Here’s a simplified example of this: • With AGP, the graphics card can receive a request for all of the information needed to render a particular image and send it out all at once. With PCI, the graphics card would receive information on the height of the image and wait… then the length of the image, and wait … then the width of the image, and wait … combine the data, and then send it out. 90006 90007 90032 90003 90004 Hardware II 90005 Computer Graphics 3. Sideband addressing Like a letter, all requests and information sent from one part of your computer to the next must have an address containing «To» and «From.» The problem with PCI is that this «To» and «From» information is sent with the working data all together in one packet.This is the equivalent of including an address card inside the envelope when you send a letter to a friend: Now the post office has to open the envelope to see the address in order to know where to send it. This takes up the post office’s time. In addition, the address card itself takes up room in the envelope, reducing the total amount of stuff you can send to your friend. With sideband addressing, the AGP issues eight additional lines on the data packet just for addressing. This puts the address on the outside of the envelope, so to speak, freeing up the total bandwidth of the data path used to transfer information back and forth.In addition, it unclogs system resources that were previously used to open the packet to read the addresses. 90006 90007 90038 90003 90004 Hardware II 90005 Computer Graphics AGP: Saves RAMAGP improves the process of storing texture maps by allowing the Operating System to designate RAM for use by the graphics card on the fly. This type of memory is called AGP memory or non-local video memory. Using the much more abundant and faster RAM used by the operating system to store texture maps reduces the number of maps that have to be stored on the graphics card’s memory.In addition, the size of the texture map your computer is capable of processing is no longer limited to the amount of RAM on the graphics card. 90006 90007 90044 90003 90004 Hardware II 90005 Computer Graphics GART AGP saves RAM is by only storing texture maps once. It does this with a little trickery. This trickery takes the form of a chipset called the Graphics Address Remapping Table (GART). GART takes the portion of the system memory that the AGP borrows to store texture maps for the graphics card and re-addresses it.The new address provided by GART makes the CPU think that the texture map is being stored in the card’s frame buffer. GART may be putting bits and pieces of the map all over the system RAM; but when the CPU needs it, as far as it’s concerned the texture map is right where it should be. 90006 90007 90050 90003 90004 Hardware II 90005 Computer Graphics PCI (Peripheral Component Interconnect) Express Card PCI Express is a serial connection that operates more like a network than a bus.Instead of one bus that handles data from multiple sources, PCI-e has a switch that controls several point-to-point serial connections. These connections fan out from the switch, leading directly to the devices where the data needs to go. Every device has its own dedicated connection 90006 90007 90056 90003 90004 Hardware II 90005 Computer Graphics PCI Express Lanes Each lane of a PCI Express connection contains two pairs of wires — one to send and one to receive.Packets of data move across the lane at a rate of one bit per cycle. A x1 connection, the smallest PCI-e connection, has one lane made up of four wires. It carries one bit per cycle in each direction. A x2 link contains eight wires and transmits two bits at once, a x4 link transmits four bits, and so on. Other configurations are x12, x16 and x32. A x16 PCI-e connector can move 6.4 GB of data per second in each direction. 90006 90007 90062 90003 90004 Hardware II 90005 Computer Graphics Video BIOS The video BIOS or firmware contains the basic program, which is usually hidden, that governs the video card’s operations and provides the instructions that allow the computer and software to interact with the card.It may contain information on the memory timing, operating speeds and voltages of the graphics processor, RAM, and other information. 90006 90007 90068 90003 90004 Hardware II 90005 Computer Graphics Graphics Processing Unit (GPU) A GPU is a dedicated processor optimized for accelerating graphics. The processor is designed specifically to perform floating-point calculations, which are fundamental to 3D graphics rendering and 2D picture drawing. The main attributes of the GPU are the core clock frequency, which typically ranges from 250 MHz to 4 GHz and the number of pipelines (vertex and f ragment shaders), which translate a 3D image characterized by vertices and lines into a 2D image formed by pixels.Modern GPUs are massively parallel, and fully programmable. Their computing power is orders of magnitude greater than that of CPUs for certain kinds of operations. This has led to the emergence of general-purpose computing on graphics processing units (GPGPU). Occasionally called visual processing unit or VPU. 90006 90007 90074 90003 90004 Hardware II 90005 Computer Graphics Compute Unified Device Architecture (CUDA) CUDA is a parallel computing architecture developed by Nvidia for graphics processing.CUDA is the computing engine in Nvidia graphics processing units (GPUs) that is accessible to software developers through variants of industry standard programming languages. CUDA gives developers access to the virtual instruction set and memory of the parallel computational elements in CUDA GPUs. Using CUDA, the latest Nvidia GPUs become accessible for computation like CPUs. Unlike CPUs however, GPUs have a parallel throughput architecture that emphasizes executing many concurrent threads slowly, rather than executing a single thread very quickly.This approach of solving general purpose problems on GPUs is known as GPGPU. 90006 90007 90080 90003 90004 Hardware II 90005 Computer Graphics Power demand As the processing power of video cards has increased, so has their demand for electrical power. Current high-performance video cards tend to consume a great deal of power. While CPU and power supply makers have recently moved toward higher efficiency, power demands of GPUs have continued to rise, so the video card may be the biggest electricity user in a computer.Although power supplies are increasing their power too, the bottleneck is due to the PCI-Express connection, which is limited to supplying 75 Watts. Modern video cards with a power consumption over 75 Watts usually include a combination of six-pin (75W) or eight-pin (150W) sockets that connect directly to the power supply. 90006 90007 90086 90003 90004 Hardware II 90005 Computer Graphics High-Definition Multimedia Interface (HDMI) High-Definition Multimedia Interface (HDMI) An advanced digital audio / video interconnect released in 2003 and is commonly used to connect game consoles and DVD players to a display .HDMI supports copy protection through HDCP (High-bandwidth Digital Content Protection). 90006 90007 90092 90003 90004 Hardware II 90005 Computer Graphics END Hardware II 16 90006 90007.90000 PPT — Computer Graphics PowerPoint Presentation, free download 90001 90002 90003 90004 Computer Graphics 90005 Assistant Prof. Dr. Aybars UGUR 90006 90007 90008 90003 90004 Contents 90005 • What is computer Graphics • 3D Transformations • 3D Object Representations • Application Areas of Computer Graphics • Major Subfields of CG • Game Engines • 3D Application Programming Interfaces • 3D Application Programming Interfaces for Mobile Devices • Java 3D FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90014 90003 90004 Computer Graphics (CG) 90005 • Computer Graphics is a subfield of computer science.• Studies digitally synthesizing and manipulating visual content using computational techniques. • All aspects of producing pictures or image using a computer. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90020 90003 90004 3D Computer Graphics 90005 • Graphics that use a three-dimensional representation of geometric data that is stored in the computer. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90026 90003 90004 out 90005 in computer image data o i traditional computing computer graphics data computer vision image processing image What is computer graphics about? FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90032 90003 90004 y 90005 x z y P1 P1 ‘x z 3D Transformations • Some Mathematical Background Translation, Rotation Scaling, etc.FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90038 90003 90004 3D Object Representations 90005 • B-Representation • Sweep Representations • CSG Methods • Splines • Quadrics FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90044 90003 90004 (S4) Top Face 90005 Back Face (S0) y Left Face (S2) Right Face (S5) xz Bottom Face (S1) (S3) Front Face Boundary Representations (B-rep) • Describe a 3D object as a set of surfaces that seperate the object interior from the environment. • A cuboid consists of six faces or rectangular polygons (front, left, back or rear, right, bottom, and top), eight vertices, and twelve edges.FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90050 90003 90004 Sweep Representations 90005 • Idea is to define a 2D shape and then a sweep which will move the shape through 3D space to create a 3D object. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90056 90003 90004 Sweep Representations 90005 • A sweep can follow any path. • The object being swept can vary in size along the path. • A simple 2D curve can produce interesting3D shapes. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90062 90003 90004 Constructive Solid-Geometry Methods (CSG) 90005 • Given two 3D objects, create new ones with the set operations of • union • intersection • difference Top subtracted from bottom yields A flute made from a cylinder, 1 ellipsoid and 8 circles where the ellipsoid and 8 circles are subtracted from the cylinder.FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90068 90003 90004 What is a Spline Curve? 90005 • In computer graphics, the term refers to any composite curve formed with polynomial sections satisfying some specified continuity conditions at the boundary of the pieces. • There are many different types of spline curves and we will investigate only a few of them here. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90074 90003 90004 Interpolating and Approximating Splines 90005 • We specify a spline curve by giving a set of coordinate positions in 2D.• The coordinates are either interpolated or approximated using points called control points. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90080 90003 90004 Interpolating and Approximating 90005 • Interpolation is often used to digitize drawings or specify animation paths. • Approximation is used predominately as a design tool to create object shapes. • Although we are talking about curves right now, these curves can be used to create 3D surfaces such as FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90086 90003 90004 Working with Splines 90005 • Spline curves (and surfaces) are defined, modified, and manipulated with operations on the control points.• The designer selects (often interactively) locations for the control points and these influence the position and shape of the curve. • By repositioning the control points, the curve can be shaped by eyeballing it and adjusting its shape until it is what is desired. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90092 90003 90004 Splines Have Many Nice Characteristics for Graphics 90005 • Geometric transformations only must be applied to the control points and then the curve can be regenerated — i.e splines can be manipulated easily just like polygons. • Given a set of points, the convex hull of the points (in 2D) is the smallest set containing all the points that is convex. • Intuitively, think of a rubber band being stretched to include all the points — that would define the convex hull. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90098 90003 90004 Splines Have Many Nice Characteristics for Graphics 90005 • For most splines, the curve lies in the convex hull of the control points This property means the curve will not deviate too far from the control points.In particular, wild oscillations will not occur. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90104 90003 90004 3D Graphics Pipeline 90005 WORLD SCENE / OBJECT Modelling coordinates: — world coordinate system, — object coordinate system 3D MODELLING VIEWING 3D CLIPPING Camera coordinates PROJECTION Screen / Window coordinates RASTERIZATION Device coordinates 2D PIXELMAP DISPLAY FACHHOCHSCHULE GIESSEN- FRIEDBERG 90006 90007 90110 90003 90004 Application Areas of Computer Graphics 90005 • CAD — Computer Aided Design • Education and Training • Entertainment • Scientific Visualization • Virtual Reality • Web and Web3D FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90116 90003 90004 CAD (Computer Aided Design) 90005 is the use of computer technology to aid in the design of a product.Some Fields of Use: • The Architecture, Engineering, and Construction Industry • Mechanical Engineering • Product Design (Textile, Food, Computers, Electronic Devices, etc.) • Automotive, Aerospace, … FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90122 90003 90004 CAD — I 90005 Los Angeles Airport FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90128 90003 90004 CAD — II 90005 Boeing 777 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90134 90003 90004 Entertainment — I 90005 Computer Graphics in movie industry FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90140 90003 90004 Entertainment 90005 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90146 90003 90004 Entertainment — II 90005 Games FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90152 90003 90004 Education and Training — I 90005 • Computer generated models of physical, financial, political, social, economic, and other systems are often used as educational aids.• Aircraft, naval, and spacecraft simulators • Simulators for practice sessions or training of ship captains, aircraft pilots, heavy equipment operators, and air traffic control personnel. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90158 90003 90004 Education and Training — II 90005 Flight Simulator FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90164 90003 90004 Virtual Reality (VR) 90005 Virtual Reality (VR) is a computer system used to create an artificial world in which the user has the impression of being in that world and with the ability to navigate through the world and manipulate objects in the world.VR is a technology, which allows a user to interact with a computer simulated environment, be it a real or imagined one. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90170 90003 90004 Data Gloves, Head Mounted Display 90005 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90176 90003 90004 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90005 90006 90007 90182 90003 90004 HMD 90005 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90188 90003 90004 Scientific VisualizationI 90005 • Scientific, engineering and medical data.• High number of data. • Complex structures (medical, …) • Simulation of complex process • Complex molecular structure • such as protein and DNA • weather forecasting • Complex mathematical object FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90194 90003 90004 Web and Web3D 90005 The Web3D Consortium is an international organization established to define and promote standards for 3D graphics representation on the World Wide Web. From the perspective of the Web3D Consortium, «Web3D» is an overarching term to describe protocols, languages, file formats, and other technologies that are used to deliver compelling 3D content over the World Wide Web.X3D, Java 3D and VRML are some of the key Web 3D Technologies. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90200 90003 90004 Major subfields of CG 90005 • Geometry (studies representation of three-dimensional objects) • Animation (studies descriptions for surfaces that move or deform over time) • Rendering • Imaging FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90206 90003 90004 Rendering 90005 • Converts a model into an image • Result is physically-based photorealistic images Illumination, Reflection, Refraction, etc.FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90212 90003 90004 Texture Mapping 90005 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90218 90003 90004 Ray Tracing 90005 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90224 90003 90004 Image Processing 90005 Image processing is any form of signal processing for which the input is an image, such as photographs or frames of video; the output of image processing can be either an image or a set of characteristics or parameters related to the image.FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90230 90003 90004 Vector Graphics vs. Raster Graphics 90005 • Macromedia flash is vector based • JPG images are raster based • Time to transmit vs. time to generate • Reuse of image description FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90236 90003 90004 Vector Graphics 90005 • A line is represented by endpoints (20,20) to (100,100) • If you want the image larger, no problem … FACHHOCHSCHULE GIESSEN- FRIEDBERG 90006 90007 90242 90003 90004 Raster Graphics 90005 • A line is represented by assigning some pixels a value of 1.• The entire line is specified by the pixel values ​​• What do we do to make image larger? FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90248 90003 90004 Colors 90005 • Color in CG is commonly specified in RGB format. • A color in RGB format is a triplet of numbers. The three components are Red, Green and Blue. • Other Color Models? Blue Red Green FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90254 90003 90004 GAME ENGINES 90005 • Game Engine • 3D engine • Sound Engine • Input Engine • Network Engine • Physics Engine • AI Engine • GUI Engine FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90260 90003 90004 TORQUE GAME ENGINE 90005 GAME ENGINE MAP EDITOR TEXTURE GENERATORS MODEL GENERATORS FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90266 90003 90004 3D Application Programming Interfaces 90005 For writing applications that produce 2D and 3D computer graphics.• PHIGS (1990’s) • OPENGL was developed by Silicon Graphics Inc. (SGI) in 1992 and is widely used in CAD, VR, scientific visualization, It is also used in video games, where it competes with Direct3D on MS Windows platforms • Java 3D is a scene graph-based 3D application programming interface (API) for the Java platform. It runs on top of either OpenGL or Direct3D. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90272 90003 90004 Java-based 3D APIs 90005 • Java 3D is not the only high-level API option to render 3D in Java.In part due to the pause in development during 2003 and 2004, several competing Java scene graph technologies emerged: • General purpose: • AgentFX • Strata Live 3D • Gaming: • Xith 3D • jMonkey Engine • Espresso3D • Visualization: • Aviatrix 3D • JView • Jreality. http://www3.math.tu-berlin.de/jreality/ JOGL is a popular alternative to scene graph APIs FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90278 90003 90004 3D Application Programming Interfaces For Mobile Devices 90005 • The Mobile 3D Graphics API, commonly referred to as M3G, is a specification defining an API for writing Java programs that produce 3D computer graphics.M3G is not Java 3D. M3G was designed to meet the specific needs of mobile devices, which are constrained in terms of memory, memory bandwidth, and processing power. • OpenGL ES (OpenGL for Embedded Systems) is a subset of the OpenGL 3D graphics API designed for embedded devices such as mobile phones, PDAs, and video game consoles. FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90284 90003 90004 Java 3D 90005 90006 90007 90290 90003 90004 3D Application Programming Interfaces For Mobile Devices 90005 FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 90296 90003 90004 Java3D’s SceneGraph 90005 VirtualUniverse Locale Root group BG BG TG robot arm environment TG TG view sphere TG base SS TG bottom arm S up arm S FACHHOCHSCHULE GIESSEN-FRIEDBERG 90006 90007 Load More….90000 PPT — Computer Graphics PowerPoint Presentation, free download 90001 90002 90003 90004 Computer Graphics 90005 Lecture Notes # 16 Image-Based Modelling, Rendering and Lighting 90006 90007 90008 90003 90004 Global Illumination and Image-Based Lighting 90005 • Traditional Computer Graphics involves: • Modelling with matter: geometry with reflectance properties. • Image-Based Modelling & Rendering is: • Modelling and rendering with Light, often deriving geometry and materials in the process.• Image-Based Lighting allows: • Combination of real and synthetic graphics with consistent illumination, using images as light sources. Lecture Notes # 16 90006 90007 90014 90003 90004 Pursuit of Photorealism 90005 • For complex models, tools can require lot of effort and rendering is very slow. • Choice: do usual modelling or just take a photo (that would provide photorealism!) • IBMR is about using these photos and transcending their limitations (eg. Light). • Do not need anything like a complete model, but may need a number of photographs … Lecture Notes # 16 90006 90007 90020 90003 90004 Pursuit of Photorealism 90005 • Need enough photographs to give coverage.• Major result is — rendering is faster. • So Image-Based Modelling and Rendering (IBMR) starts with the answer! • Research inspired by film industry. • Related to techniques in Computer Vision. • New so no taxonomy, just techniques. Lecture Notes # 16 90006 90007 90026 90003 90004 IBMR Techniques 90005 • Panoramas — movement within and between panoramic cylinders, eg. Quicktime VR. • Panoramas can be real or synthetic. • View interpolation -from a few photos, interpolate view from any position (morphing).• * Lighting — adding real or synthetic objects to a photographed scene, illuminated with scene lights. • Modelling — extracting models from photos. Lecture Notes # 16 90006 90007 90032 90003 90004 «Traditional graphics» 90005 Lecture Notes # 16 90006 90007 90038 90003 90004 Computer Vision 90005 Lecture Notes # 16 90006 90007 90044 90003 90004 Vision meets graphics 90005 Lecture Notes # 16 90006 90007 90050 90003 90004 However. .. 90005 • Vision falls short Lecture Notes # 16 90006 90007 90056 90003 90004 And… 90005 … so does graphics Lecture Notes # 16 90006 90007 90062 90003 90004 Image-Based Rendering (IBR) 90005 Lecture Notes # 16 90006 90007 90068 90003 90004 What is an image? 90005 • Collection of radiance values ​​• radiance along a ray • 3D position • 2D direction Lecture Notes # 16 90006 90007 90074 90003 90004 Plenoptic function 90005 • Radiance value for all possible rays = plenoptic function. • All possible images are a subset of this plenoptic function. • Too much stuff! • Goal of IBR is generate a continuous representation of the plenoptic function.Lecture Notes # 16 90006 90007 90080 90003 90004 Plenoptic function 90005 • Radiance is constant along a ray (line) • 2D position • 2D direction Once we know one ‘origin’, we know them all Lecture Notes # 16 90006 90007 90086 90003 90004 What is an image? 90005 • Image = rays going through one point • usually restricted to viewing frustum, but can also be panoramic Lecture Notes # 16 90006 90007 90092 90003 90004 What is an object? 90005 • Image = rays going through one point + image plane • 2D function (position on image plane) Lecture Notes # 16 90006 90007 90098 90003 90004 What is an object? 90005 • Outgoing radiance field of an object • 2D function (position on surface) Lecture Notes # 16 90006 90007 90104 90003 90004 What is an object? 90005 • All light leaving the object Lecture Notes # 16 90006 90007 90110 90003 90004 What is an object? 90005 • All light leaving the object • 4D function (2D position + 2D direction) Lecture Notes # 16 90006 90007 90116 90003 90004 What is an object? 90005 • All possible images of an object Lecture Notes # 16 90006 90007 90122 90003 90004 What is an object? 90005 • All possible images of an object Lecture Notes # 16 90006 90007 90128 90003 90004 What is an object? 90005 • We do not really need the object Lecture Notes # 16 90006 90007 90134 90003 90004 What is an object? 90005 • We do not really need the object Lecture Notes # 16 90006 90007 90140 90003 90004 Lumigraph / Light Field 90005 • Object is only defined by its radiance field stuff 4D function (Levoy — Cohen et al 96) Lecture Notes # 16 90006 90007 90146 90003 90004 Lumigraph — capture 90005 (Stanford — Levoy et al.) Lecture Notes # 16 90006 90007 90152 90003 90004 Layered Depth Images 90005 (McMillan) • Problem with one photo is «holes» when view point moved: • this is why a number of photos are generally required • fill the holes using intensities of neighbouring pixels • interpolation … Lecture Notes # 16 90006 90007 90158 90003 90004 Image Based Lighting 90005 • Add models or objects to scenes and allow them to be manipulated in the scenes. • Modelling with light allows added objects to be illuminated consistent with image existent lighting — photorealistic inclusions.• We start with the answer by finding the scene illumination. Lecture Notes # 16 90006 90007 90164 90003 90004 Image Based Lighting 90005 (all pictures P. Debevec 98-99) • Real Scene • Goal: place synthetic objects on table Lecture Notes # 16 90006 90007 90170 90003 90004 Extracting scene lighting 90005 • Capture illumination using illumination sphere Lecture Notes # 16 90006 90007 90176 90003 90004 Real scene 90005 Image Based Lighting Lecture Notes # 16 90006 90007 90182 90003 90004 Image Based Lighting 90005 captured illumination field Lecture Notes # 16 90006 90007 90188 90003 90004 Image Based Lighting 90005 light based model synthetic objects local scene Real scene Lecture Notes # 16 90006 90007 90194 90003 90004 light based model 90005 Image Based Lighting • Use renderer — compute effects of synthetic objects on local scene synthetic objects (brdf known) local scene (brdf estimated) Lecture Notes # 16 90006 90007 90200 90003 90004 Image Based Lighting 90005 • Render into the scene background Lecture Notes # 16 90 006 90007 90206 90003 90004 Image Based Lighting 90005 • Render synthetic objects Lecture Notes # 16 90006 90007 90212 90003 90004 Image Based Lighting 90005 • Effect of local scene on real scene Lecture Notes # 16 90006 90007 90218 90003 90004 Image Based Lighting 90005 • Add differences to image Lecture Notes # 16 90006 90007 90224 90003 90004 Reconstruction from images? 90005 • Computer Vision related.• Constructs new views and extracts models. • Epipolar geometry • expresses relationships between points in different images. • Difficult to predict full impact in CG. • State of the Art • 3D reconstruction from uncalibrated images. Lecture Notes # 16 90006 90007 90230 90003 90004 References 90005 • You will not find this material in the major graphics texts since it is new and not yet mainstream but I recommend the following: • The Computer Image, Watt & Policarpo, Addison-Wesley 1998. • SIGGRAPH courses for the past few years, we have some on CD rom and on-line within EdVEC and not immediately available to Informatics machines — ask me if you have a strong interest and need.Lecture Notes # 16 90006 90007.90000 PPT — Computer Graphics PowerPoint Presentation, free download 90001 90002 90003 90004 Lecture 5 90005 Hidden Surface Removal and Rasterization Taku Komura Computer Graphics 90006 90007 90008 90003 90004 Hidden surface removal 90005 • Drawing polygonal faces on screen consumes CPU cycles • Illumination • We can not see every surface in scene • We do not want to waste time rendering primitives which do not contribute to the final image. 90006 90007 90014 90003 90004 Visibility (hidden surface removal) 90005 • A correct rendering requires correct visibility calculations • Correct visibility • when multiple opaque polygons cover the same screen space, only the closest one is visible (remove the other hidden surfaces) • wrong visibility correct visibility 90006 90007 90020 90003 90004 Visibility of primitives 90005 • A scene primitive can be invisible for 3 reasons: • Primitive lies outside field of view • Primitive is back-facing • Primitive is occluded by one or more objects nearer the viewer 90006 90007 90026 90003 90004 Visible surface algorithms.90005 • Definitions: • Object space techniques: applied before vertices are mapped to pixels • Back face culling, Painter’s algorithm, BSP trees • Image space techniques: applied while the vertices are rasterized • Z-buffering 90006 90007 90032 90003 90004 Back face culling. 90005 • The vertices of polyhedra are oriented in an anticlockwise manner when viewed from outside — surface normal N points out. • Project a polygon. • Test z component of surface normal. If negative — cull, since normal points away from viewer.• Or if N.V> 0 we are viewing the back face so polygon is obscured. 90006 90007 90038 90003 90004 Painters algorithm (object space). 90005 • Draw surfaces in back to front order — nearer polygons «paint» over farther ones. • Supports transparency. • Key issue is order determination. • Does not always work — see image at right. 90006 90007 90044 90003 90004 BSP (Binary Space Partitioning) Tree. 90005 • One of class of «list-priority» algorithms — returns ordered list of polygon fragments for specified view point (static pre-processing stage).• Choose polygon arbitrarily • Divide scene into front (relative to normal) and back half-spaces. • Split any polygon lying on both sides. • Choose a polygon from each side — split scene again. • Recursively divide each side until each node contains only 1 polygon. 5 2 3 1 4 View of scene from above 90006 90007 90050 90003 90004 Lecture 9 90005 5 5a 5b 2 3 1 4 3 back front 1 2 5a 4 5b BSP Tree. • Choose polygon arbitrarily • Divide scene into front (relative to normal) and back half-spaces.• Split any polygon lying on both sides. • Choose a polygon from each side — split scene again. • Recursively divide each side until each node contains only 1 polygon. 90006 90007 90056 90003 90004 BSP Tree. 90005 5 5a 5b 2 • Choose polygon arbitrarily • Divide scene into front (relative to normal) and back half-spaces. • Split any polygon lying on both sides. • Choose a polygon from each side — split scene again. • Recursively divide each side until each node contains only 1 polygon. 3 1 4 3 back front 2 4 5b front 5a 1 90006 90007 90062 90003 90004 5 90005 5a 5b 2 3 1 4 3 back front 2 4 front 5a 1 5b BSP Tree.• Choose polygon arbitrarily • Divide scene into front (relative to normal) and back half-spaces. • Split any polygon lying on both sides. • Choose a polygon from each side — split scene again. • Recursively divide each side until each node contains only 1 polygon. 90006 90007 90068 90003 90004 Lecture 9 90005 Displaying a BSP tree. • Once we have the regions — need priority list • BSP tree can be traversed to yield a correct priority list for an arbitrary viewpoint. • Start at root polygon.• If viewer is in front half-space, draw polygons behind root first, then the root polygon, then polygons in front. • If polygon is on edge — either can be used. • Recursively descend the tree. • If eye is in rear half-space for a polygon — then can back face cull. 90006 90007 90074 90003 90004 Lecture 9 90005 BSP Tree. • A lot of computation required at start. • Try to split polygons along good dividing plane • Intersecting polygon splitting may be costly • Cheap to check visibility once tree is set up.• Can be used to generate correct visibility for arbitrary views. • Efficient when objects do not change very often in the scene. 90006 90007 90080 90003 90004 Lecture 9 90005 BSP performance measure • Tree construction and traversal (object-space ordering algorithm — good for relatively few static primitives, precise) • Overdraw: maximum • Front-to-back traversal is more efficient • Record which region has been filled in already • Terminate when all regions of the screen is filled in • S.Chen and D. Gordon. «Front-to-Back Display of BSP Trees.» IEEE Computer Graphics & Algorithms, pp 79-85. September 1991. 90006 90007 90086 90003 90004 Z-buffering: image space approach 90005 Basic Z-buffer idea: • rasterize every input polygon • For every pixel in the polygon interior, calculate its corresponding z value (by interpolation) • Track depth values of closest polygon (smallest z) so far • Paint the pixel with the color of the polygon whose z value is the closest to the eye.90006 90007 90092 90003 90004 Implementation. 90005 • Initialise frame buffer to background colour. • Initialise depth buffer to z = max. value for far clipping plane • For each triangle • Calculate value for z for each pixel inside • Update both frame and depth buffer 90006 90007 90098 90003 90004 Filling in Triangles 90005 • Scan line algorithm • Filling in the triangle by drawing horizontal lines from top to bottom • Barycentric coordinates • Checking whether a pixel is inside / outside the triangle 90006 90007 90104 90003 90004 Triangle Rasterization 90005 • Consider a 2D triangle with vertices p0, p1, p2.• Let p be any pointin the plane. We can always find a, b, c such that • We will haveif and only if p is inside the triangle. • We call thebarycentric coordinates of p. 90006 90007 90110 90003 90004 Computing the baricentric coordinates of the interior pixels 90005 • (α, β, γ): barycentric coordinates • Only if 0 <α, β, γ <1, (x, y) is inside the triangle • Depth can be computed by αZ0 + βZ1 + γZ2 • Can do the same thing for color, normals, textures • The triangle is composed of 3 points p0 (x0, y0), p1 (x1, y1), p2 (x2, y2) 90006 90007 90116 90003 90004 Bounding box of the triangle 90005 • First, identify a rectangular region on the canvas that contains all of thepixels in the triangle (excluding those that lie outside the canvas).• Calculate a tight bounding box for a triangle: simply calculate pixelcoordinates for each vertex, and find the minimum / maximum for each axis 90006 90007 90122 90003 90004 Scanning inside the triangle 90005 • Once we've identified the bounding box, we loop over each pixel in the box. • For each pixel, we first compute the corresponding (x, y) coordinates in the canonical view volume • Nextwe convert these into barycentric coordinates for the triangle being drawn. • Only if the barycentric coordinates are within the range of [0,1], we plot it (and compute the depth) 90006 90007 90128 90003 90004 Why is z-buffering so popular? 90005 Advantage • Simple to implement in hardware.• Memory for z-buffer is now not expensive • Diversity of primitives - not just polygons. • Unlimited scene complexity • Do not need to calculate object-object intersections. Disadvantage • Extra memory and bandwidth • Waste time drawing hidden objects Z-precision errors • May have to use point sampling 90006 90007 90134 90003 90004 Z-buffer performance 90005 • Brute-force image-space algorithm scores best for complex scenes -easy to implement and is very general. • Storage overhead: O (1) • Time to resolve visibility to screen precision: O (n) • n: number of polygons 90006 90007 90140 90003 90004 Lecture 9 90005 Ex.Architectural scenes Here there can be an enormous amount of occlusion 90006 90007 90146 90003 90004 Lecture 9 90005 Occlusion at various levels 90006 90007 90152 90003 90004 A 90005 BCDE Portal Culling (object-space) DF • Model scene as a graph: • Nodes: Cells (or rooms) • Edges: Portals (or doors) • Graph gives us: • Potentially visible set • Render the room • If portal to the next room is visible, render the connected room in the portal region • Repeat the process along the scene graph BECGA 90006 90007 90158 90003 90004 Summary 90005 • Z-buffer is easy to implement on hardware and is an important tool • We need to combine it with an object-based method especially when there are too many polygons • BSP trees, portal culling 90006 90007 90164 90003 90004 References for hidden surface removal 90005 • Foley et al.Chapter 15, all of it. • Introductory text, Chapter 13, all of it • Baricentric coordinates www.cs.caltech.edu/courses/cs171/barycentric.pdf • Or equivalents in other texts, look out for: • (as well as the topics covered today) • Depth sort - Newell, Newell & Sancha • Scan-line algorithms 90006 90007.