CSI-447: Multimedia Systems Chapter_3_A: Graphics and Images

Computer Graphics Vector Graphics Bitmap Images Combining vectors and bitmaps

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

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

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

… 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

… 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

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

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

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

… 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

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

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

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