1. CSI-447: Multimedia Systems
Chapter_3_A: Graphics and Images

2. Computer Graphics Vector Graphics Bitmap Images
Combining vectors and bitmaps

3. Models of Bitmapped Graphics
modeled by an array of pixel values
Bitmapped graphics does not use bitmaps (except for pure monochrome images) it use pixel maps

4. Models of Vector Graphics
stored as a mathematical description of a collection of individual lines, curves and shapes making up the image
e.g. line = two end points
Displaying a vector image
requires some computation to be performed in order to interpret the model and generate an array of pixel to be displayed
The process of interpreting the vector description known as rasterizing

5. Vector Graphics Scalable Resolution independent No background
Cartoon-like
Inappropriate for photo-realistic images
Metafiles contain both raster and vector data

6. … Vector Graphics Points can be identified by coordinates
Lines and shapes can be described by equations
Approximating abstract shapes on a grid of finite pixels leads to `jaggies‘
Anti-aliasing can offset this effect
Bezier curves are drawn using four control points
Bezier curves can be made to join together smoothly into paths
Paths and shapes can be stroked and filled

7. … Vector Graphics Geometrical transformations
translation, scaling, rotation, reflection and shearing - can be applied easily to vector shapes
Three approaches to 3-D modeling
constructive solid geometry
free-form modeling
procedural modeling
3-D rendering models the effect of light and texture, as well as displaying the modeled objects in space
Ray tracing and radiosity are computationally expensive rendering algorithms that can produce photo-realistic results

8. Vector Graphics Tools Adobe Illustrator CorelDraw Macromedia FreeHand
XARA X
Most can export your work to bitmap images

9. Metafile Format Used for vector graphics Can embed bitmap images
Collection of Graphics Device Interface (GDI) functions
“Rasterization” process
Default extension .WMF
Less space
Structure
header
size of the file
# of drawing objects
list of records

10. Other Common Vector File Formats
CGM
Computer Graphics Meta File
DRW
Micrographics Designer file format
CDR
CorelDRAW native format
HPGL
HP plotter print format
DXF
Drawing Exchange Files
created by Autodesk for AutoCAD

11. … Other Common Vector File Formats
EPS
Encapsulated PostScript Files
developed by Adobe Systems for compatibility with PostScript lang
device independent
may contain a TIFF or WMF image for screen presentation AI
Illustrator native format

12. 3-D Graphics 2D: define shapes by paths 3D: define objects by surfaces
Hierarchical modeling
– A bicycle consists of a frame, two wheels, …

13. Rendering
In 3D, we have a mathematical model of objects in space, but we need a flat picture
Viewpoint
Position of camera
Scaling with distance
Lighting: position, intensity, type
Interaction of light: underwater, smoke-filled room
Texture

14. … Rendering Wire frame Hidden surface removal Surface properties
Color and reflectivity
Lights
Shading
A color for each polygon
Interpolate color