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Computer Graphics

Computer Graphics. Chapter 1: Introduction to Graphics. Computer graphics History. Computer graphics generally means creation, storage and manipulation of models and images

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Computer Graphics

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  1. Computer Graphics

  2. Chapter 1: Introduction to Graphics

  3. Computer graphics History • Computer graphics generally means creation, storage and manipulation of models and images • Such models come from diverse and expanding set of fields including physical, mathematical, artistic, biological, and even conceptual (abstract) structures Frame from animation by William Latham, shown at SIGGRAPH 1992. Latham uses rules that govern patterns of natural forms to create his artwork.

  4. Graphics Library (GL) • Examples: OpenGL™, DirectX™, Windows Presentation Foundation™ (WPF), RenderMan™ • Primitives (chars, lines, polygons, meshes,…) • Attributes • color • line style • material properties for 3D • Lights • Transformations • Immediate mode vs. retained mode • immediate mode: no stored representation, package holds only attribute state, and application must completely draw each frame • retained mode: library compiles and displays from scene graph that it maintains, a complex DAG. It is a display-centered extract of the Application Model

  5. What is computer graphics

  6. Some research fields of computer graphics

  7. Basic notions • Computer graphics – process of producing a picture or image using the computer • Computer interfaces popular on personal computers • Desktop publishing • Realistic images generated using mathematical and physical methods

  8. Steps for creating a picture • Creating a model • Perform necessary transformation • Lighting and rendering the object • The goal is the creation of an image by writing a program instead of taking a picture with a camera • There exists an analogy between writing graphical programs and taking pictures by a camera

  9. Pixels • Pixel or “Picture element” is the simplest element in computer graphics • Single location on the computer screen or printout • Value of each pixel is the range from white to black or range of intensities of red, green, blue (RGB) colors.

  10. Frame buffers • The pixels of an image are organized into two dimensional grid – frame buffer • Multiple frame buffers can be stored in computer memory • Double buffering – first image is drawn into frame buffer and sent to display. While the user is looking on the display, the next picture is drawing to the second buffer.

  11. Windows • Image don’t fill the entire screen but is drawn into a window • Pixels are adressed within the window based on their location • Relative position of each pixel enables moving the window and change its size

  12. Realistic images • Calculating pixel values to create impression of a realistic picture • Simulation of objects from the real word • Approximation of physical properties of objects • Limitations given by computing time and memory space

  13. The Graphics Pipeline • Modeling – creates an internal representation of the objects in the scene • Rendering – converts the screen description into image • Display – shows the image on the output device

  14. The Graphics Pipeline Model Transformation Object Specification Scene Description Scene Description Clipping and Hidden Surface Removal Model Transformation View and Light Specification Image Shading

  15. The Graphics Pipeline Image Display Transformation Output

  16. Applications of Computer Graphics • Display of information • Design • Simulation and animation • User interfaces

  17. Display of information • Maps • GIS (geographic information system) • CT (computer tomography) • MRI (magnetic resonance imaging) • PET (positron-emission tomography) • Fluid flow, molecular biology, mathematics…

  18. Display of Information

  19. Applications of Computer Graphics. • Design • CAD (computer-aided design): VLSI (very-large-scale integrated) circuits • Together with other tools:architecture or interior design

  20. Interior Design

  21. Applications of Computer Graphics • Simulation and animation • Flight simulation – pilot training • Games and educational software • Benefits: • Less cost • Less danger, e.g. combination with the VR (virtual reality) techniques can help surgical interns and astronauts

  22. Applications of Computer Graphics • User interfaces • Friendly working environment:windows, icons, menus, pointing devices Interface for a painting program

  23. Application Programmer’s Interface • The OpenGL graphics system is an Application Programming Interface (API) to graphics hardware. Specifications of the functions in the graphics library

  24. Three-dimensional APIs • Objects • Viewers • Light sources • Material properties

  25. Camera(Viewer) Specifications • Position (COP) • Orientation • Focal length • Film plane

  26. Sequence of Images • Wireframe • Flat shading • HSR (Hidden surface removal) • Smooth shading • Curves and surfaces • NURBS, Bezier curves/surfaces • Texture mapping • Bump mapping, environmental maps, antialiasing…

  27. Pixels

  28. A Graphics System

  29. Frame Buffer • High-end systems: VRAM or DRAM • Simpler systems: part of memory • Depth: the number of bits per pixel • True color: depth=24 • Resolution: the number of pixels in the frame buffer

  30. Rasterization or Scan-conversion • Conversion of geometric entities to pixels in the frame buffer • High-end systems • Special-purpose processors • Simpler systems • A single and shared processor

  31. Output Devices CRT (Cathode-ray tube)

  32. Output Devices • CRT • Refresh: at least 50 times per second • Interlace and non-interlace systems • Color CRTs have three colored phosphors and a shadow mask • Other raster devices: • LCD (liquid-crystal displays) • Plasma panels and digital projection systems • Non-refreshable: printers and plotters

  33. Shadow-mask CRT

  34. Input Devices • Mouse • Joystick • Data tablet • Anything else? • Hand • Foot • Voice • Mind?

  35. Images: Physical and Synthetic • Image formation • Lighting • Shading • Properties of materials

  36. Objects and Viewers • Object: formed from geometric primitives • Points, lines, polygons • Vertex (pl. Vertices) is the most primitive one • Viewer: • Locations • Viewing angles

  37. Objects and Viewers

  38. Objects and Viewers 3D world  2D image

  39. Light and Images

  40. Synthetic-camera Model Film Plane Projection Plane

  41. Single Point Light Source

  42. Ray Tracing • Penetrating transparent surfaces • Reflected by • Mirrors • Diffuse surfaces • Refracted • Absorbed

  43. Human Visual System Visual system does not have the same response to each color. We are most sensitive to green light

  44. Pinhole Camera

  45. Pinhole Camera  (xp, yp, -d) is the projection of (x, y, z)

  46. Synthetic-camera Model Bellows Camera Projector

  47. Synthetic-camera Model COP(Center of Projection) Focal Length

  48. Synthetic-camera Model Film Plane Projection Plane

  49. Synthetic-camera Model Clipping Window

  50. Sequence of Images • Wireframe • Flat shading • HSR (Hidden surface removal) • Smooth shading • Curves and surfaces • NURBS, Bezier curves/surfaces • Texture mapping • Bump mapping, environmental maps, antialiasing…

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