Computer Graphics
Introduction
Graphics: All aspects of the production
of pictures (images) using a computer
Application areas:
Display of Information
Design
Simulation
User Interfaces
Basic Graphics System:
Processor
Memory
Frame buffer
Output device
Input device
Pixels & Frame buffer
Raster: array of pixels
Pixel: picture element
Frame Buffer: memory area used to store
pixel/raster data
VRAM: Video random access memory
DRAM: Dynamic random access memory
Depth: number of bits of information stored
for each pixel
Resolution: number of pixels in frame
buffer (on screen)
Processor:
- may be main CPU or special purpose
processor on video card
- performs Rasterization (Scan Conversion)
conversion of geometric primitives (line,
circle, etc) to pixel values in frame buffer
Output devices
CRT: Cathode Ray Tube
refresh
flicker
triads
shadow mask
LCD: Liquid crystal display
Refresh
RASTER SCAN
Output devices
CRT: Cathode Ray Tube
refresh
flicker
triads
shadow mask
TRIAD
SHADOW
MASK
Vector Displays
graphics primitives are made of
sequences of strokes or vectors
Raster Displays
display graphics primitives in a
refresh buffer in terms of the
primitive’s component pixels
Vector Displays
graphics primitives are made of
sequences of strokes or vectors
IDEAL LINE DRAWING
RANDOM SCAN
Raster Displays
display graphics primitives in a
refresh buffer in terms of the
primitive’s component pixels
IDEAL LINE DRAWING
RASTER SCAN
Raster Displays
display graphics primitives in a
refresh buffer in terms of the
primitive’s component pixels
IDEAL LINE DRAWING
FILLED RASTER SCAN
IMAGES:
Point: a location on an object (or in space) relative to a
Reference Coordinate System
Cartesian Coordinates: 3D space, perpendicular
axes, equal distance measures on each axis
Object: specified by an organized grouping of Metric
and topological information
Vertices: corner points. They carry metric information - (X,Y,Z) coordinates.
Vertex listing: list of vertex identifiers forming polygon
boundary (usually a list of indices into the vertex array)
Image creation:
NOTE: An image is generally a 2D projection or
rendering of a 3D scene
What must be specified (known)
1
1 -- What
What are
are the
the objects
objects in
in the
the scene
scene
2
objects in
in the
2 -- Where
Where are
are the
the objects
the scene
scene
3
3 -- Where
Where is
is the
the viewer
viewer
4
4 -- Where
Where is
is the
the viewer
viewer looking
looking
5 - What type of projection is assumed
6 - Where are the lights
7 - ....
Light: visible part of the electromagnetic
spectrum
Wavelength: identifies light color
(350-780 nanometers)
Light sources characterized by location,
nature (point or area), color, brightness
(Simplifying assumption for now -- assume
monochromatic (single color) lights)
Ray tracing is a method for following the path of a
photon from its origin at a light source, bouncing
off the various surfaces it strikes, before it strikes
the image plane.
The Pinhole Camera
Simple model for a camera.
Film
Pinhole
The pinhole allows only a small number of light
rays to pass through from the scene to the film.
Computer graphics model of pinhole camera
Eye
The pinhole is replaced by the eye and the film
plane moves out in front of the pinhole (eye).