Introduction

Tom Kelliher, CS 320

Jan. 28, 2000

Administrivia

Announcements

Fourth and Pixels reading.

Assignment

(Repeat) Chapters 1 and 2.

From Last Time

Terminology.

Outline

1. Graphics system architecture, CRT structure.

2. Graphics: a synthetic world.

Coming Up

OpenGL programming.

Graphics System Architecture

Overall architecture:

Hardware components:

1. Processor.

2. Memory.

3. Frame buffer.

4. Input, output devices.

CRTs

Monochrome:

1. Electron Gun.

2. Focus.

3. X-, y-deflection coils.

4. phosphor.

Color:

1. Electron gun s: R, G, B.

2. Shadow mask.

3. Triads on the phosphor.

4. Color mixing: intensity.

5. Additive effects of RGB.

6. Monitors are analog, but frame buffers are digital. ``True color.''

A Synthetic World

Here, we take a high-level view of computer graphics.

Introduction

Name two necessary components for image formation:

1. Object.

2. Viewer.

Are object and viewer sufficient? What about light? How do we model light?

Simplifications:

1. Point light sources. How good a model? Properties of light sources:
   1. Position.

   2. Intensity.

   3. Color.

   4. Directionality.

2. Monochromatic light. Not a restriction, due to additive properties of light.

Radiating Light: Ray Tracing

Rays radiate from light sources in all directions. They can:

1. Travel directly to viewer.

2. Travel to infinity, not being viewed.

3. Reflect from object and travel to viewer.

4. Pass through object and travel to viewer.

5. Interact with several objects before traveling to viewer.

6. Etc.

Material properties of object:

1. Transparent/Opaque.

2. Reflect/Diffuse.

3. Refract.

Ray tracing is a scene illuminating technique based on these ideas.

A problem: the computational complexity.

The Human Visual System

Parts of the eye:

1. Cornea.

2. Iris.

3. Lens.

4. Rods and cones.

5. Retina.

What parts does the lens play?

Three types of cones, sensitive to different light frequencies:

1. Blue --- less sensitivity.

2. Green.

3. Yellow (red).

The Pinhole Camera

Properties of a pinhole camera:

1. A perfect pinhole: only one ray from each point passes through the pinhole. Yields infinite depth of field.

2. Depth.

3. Width and height of the film.

Compute the projection of a point onto the film.

Compute the field of view.

What are the advantages/disadvantages of a lens?

The Synthetic Camera Model

Based on our pinhole camera, the model used in computer graphics.

Properties:

1. Lens

2. Bellows, allowing depth adjustment.

3. Width and height of the film.

Development:

1. Projection on the film plane may be ``reflected out front.'' This is called the projection plane.

2. Center of projection: center of lens.

3. Image on the projection plane consists of all points visible and in field of view of center of projection.

4. A clipping rectangle may be used to reduce the field of view.