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 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 Object Specification Transformation
Scene Description
Scene Description
Clipping and Hidden
Surface Removal
Model
Transformation
View and Light Specification
Shading
Image

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 Smooth 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 Other raster devices:
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 Joystick Data tablet Anything else? Hand Foot Voice
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 Viewer:
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 Refracted
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 Smooth shading
HSR (Hidden surface removal)
Smooth shading
Curves and surfaces
NURBS, Bezier curves/surfaces
Texture mapping
Bump mapping, environmental maps, antialiasing…

51. Wireframe

52. Flat Shading

53. Smooth Shading

54. Modeling With Curves/surfaces

55. Bump Mapping

56. Environmental Maps

57. Antialiasing

58. Modeling-rendering Paradigm
Example: Scene graph

59. Graphics Architecture
Compute
line segments
Very high rate
to avoid flickering
Draw
line segments
Early graphics system

60. Graphics Architecture
Display-processor architecture

61. Graphics Architecture
Arithmetic pipeline: doubling the throughput!
Pipeline Architecture: Geometric pipeline

62. Pipelining Pipeline Architecture: Geometric pipeline
Arithmetic pipeline: doubling the throughput!
Pipeline Architecture: Geometric pipeline

63. Geometric Pipeline Transformation Clipping
Conversion between coordinate systems
Translation, rotation, scaling
Aggregate transforms by matrix multiplications
Clipping
Could be further pipelined

64. Geometric Pipeline Projection Rasterization
Remaining 3D objects are projected into 2D objects
Parallel or perspective projections
Rasterization
Convert 2D objects into pixels

65. Performance Characteristics
Latency
Throughput:
How fast we can move geometric entities through the pipeline
How many pixels per second we can alter in the frame buffer
Pipeline architecture is not a must
Ray tracing or radiosity  for better quality

66. Summary & Notes of Lecture 1
Application of computer graphics
A graphics system
Human visual system
Pinhole and synthetic camera models
Image formation
Geometric pipeline
Realistic images may require resolution of up to 40006000