CG Introduction

Tom Kelliher, CS 320

Jan. 24, 2001

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Assignment

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C, OpenGL intros.

Outline

1. CG applications.

2. Graphics system components.

3. Object and images.

4. Vision.

5. Pinhole and synthetic cameras.

Coming Up

Programmer's API and CG architectures.

CG Applications

1. Entertainment: ``A Perfect Storm,'' ``The Hollow Man.''
   1. Not real-time: can use model-render paradigm.

   2. Lots of off-line compute cycles. Good physics.

   3. High quality results.

2. Games: Quake, etc.
   1. Real-time, interactive.

   2. Lots of on-line compute cycles.

   3. Procedural physics: fast, not too accurate.

      Real physics: lots of compute cycles (slow), accurate.

3. Simulation: Well, a surgical simulation is ``like'' a game.

Graphics System Components

1. Processor: General purpose CPU on motherboard and/or specialized graphics ``accelerator.''

2. Memory: Main system RAM. ``Paging device'' for frame buffer RAM. Texture maps, etc.

3. Frame buffer: Video memory. Double-buffering for animation. Texture maps, etc.

   AGP bus and main memory ``stealing.''

4. Output devices: CRT, printer, plotter, 3-D devices, etc.

   A plus if graphics sub-system is designed so that applications can be written in a device-independent way.

5. Input devices: keyboard, mouse, track ball, joy stick, data tablet, etc.

Frame buffer attributes:

1. Unit: picture element (pixel).

2. Discretization process (rasterization): geometry info to raster (array or line of pixels).

3. Depth: 1, 8, 16, 24 bits.

4. Resolution: , , , etc.

   Aspect ratio.

Objects and Images

1. In any visualization process, painting, photography, etc., there are two key elements: object and viewer.

   Object exists independently.

   Its image is dependent upon view and other things such as light.

2. In CG, an image is composed of ``polys'' --- usually triangles.

Vision

1. Human vision: rods (night) and cones (day).

   Visual acuity: resolution.

   Three types of cones, each most sensitive to a particular light frequency (blue, green, yellow).

   Response is non-linear for one type of cone and non-uniform between cones.

2. CG uses three color system of linear combinations of monochromatic red, green, blue.

Pinhole and Synthetic Cameras

Consider the project of an object of height h onto the focal plane of a pinhole camera:

1. What's the height of the image ()?

2. What's the angle of the field of view?

3. Depth of field.

4. CG's synthetic camera adds a clipping rectangle to this basic set-up.

5. Independence of objects and camera.