1 Computer Graphics Week3 –Graphics & Image Processing

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… 2

Pixels 3

A Graphics System 4

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 5

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 6

Output Devices 7 CRT (Cathode-ray tube)

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 8

Shadow-mask CRT 9

Input Devices Mouse 10 Joystick Data tablet Anything else? Hand Foot Voice Mind?

Images: Physical and Synthetic Image formation – Lighting – Shading – Properties of materials 11

Objects and Viewers Object: formed from geometric primitives – Points, lines, polygons – Vertex (pl. Vertices) is the most primitive one Viewer: – Locations – Viewing angles 12

Objects and Viewers 13

Objects and Viewers 14 3D world  2D image

Light and Images 15

16 Synthetic-camera Model Film Plane Projection Plane

Single Point Light Source 17

Ray Tracing 18 Penetrating transparent surfaces Reflected by Mirrors Diffuse surfaces Refracted Absorbed

Human Visual System 19 Visual system does not have the same response to each color. We are most sensitive to green light

Pinhole Camera 20

Pinhole Camera 21  (x p, y p, -d) is the projection of (x, y, z)

Synthetic-camera Model 22 Bellows Camera Projector

Synthetic-camera Model 23 COP(Center of Projection) Focal Length

Synthetic-camera Model 24 Film Plane Projection Plane

Synthetic-camera Model 25 Clipping Window

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… 26

Wireframe 27

Flat Shading 28

Smooth Shading 29

Modeling With Curves/surfaces 30

Bump Mapping 31

Environmental Maps 32

Antialiasing 33

Modeling-rendering Paradigm 34 Example: Scene graph

Graphics Architecture 35 Early graphics system Compute line segments Draw line segments Very high rate to avoid flickering

Graphics Architecture 36 Display-processor architecture

Graphics Architecture 37 Arithmetic pipeline: doubling the throughput! Pipeline Architecture: Geometric pipeline

Pipelining 38 Arithmetic pipeline: doubling the throughput! Pipeline Architecture: Geometric pipeline

Geometric Pipeline Transformation – Conversion between coordinate systems – Translation, rotation, scaling – Aggregate transforms by matrix multiplications Clipping – Could be further pipelined 39

Geometric Pipeline Projection – Remaining 3D objects are projected into 2D objects – Parallel or perspective projections Rasterization – Convert 2D objects into pixels 40

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 41

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 