SWE 423: Multimedia SystemsChapter 4: Graphics and Images

Computer GraphicsVector GraphicsBitmap ImagesCombining vectors and bitmaps

Models of Bitmapped Graphicsmodeled by an array of pixel valuesBitmapped graphics does not use bitmaps (except for pure monochrome images) it use pixel maps

Models of Vector Graphicsstored as a mathematical description of a collection of individual lines, curves and shapes making up the imagee.g. line = two end pointsDisplaying a vector imagerequires some computation to be performed in order to interpret the model and generate an array of pixel to be displayedThe process of interpreting the vector description known as rasterizing

Vector GraphicsScalableResolution independentNo backgroundCartoon-likeInappropriate for photo-realistic imagesMetafiles contain both raster and vector data

Vector GraphicsPoints can be identified by coordinatesLines and shapes can be described by equationsApproximating abstract shapes on a grid of finite pixels leads to `jaggies

Anti-aliasing can offset this effectBezier curves are drawn using four control pointsBezier curves can be made to join together smoothly into pathsPaths and shapes can be stroked and filled

Vector GraphicsGeometrical transformations translation, scaling, rotation, reflection and shearing - can be applied easily to vector shapesThree approaches to 3-D modelingconstructive solid geometryfree-form modelingprocedural modeling3-D rendering models the effect of light and texture, as well as displaying the modeled objects in spaceRay tracing and radiosity are computationally expensive rendering algorithms that can produce photo-realistic results

Vector Graphics ToolsAdobe IllustratorCorelDrawMacromedia FreeHandXARA XMost can export your work to bitmap images

Metafile FormatUsed for vector graphicsCan embed bitmap imagesCollection of Graphics Device Interface (GDI) functionsRasterization processDefault extension .WMFLess spaceStructureheadersize of the file# of drawing objectslist of records

Other Common Vector File FormatsCGMComputer Graphics Meta FileDRWMicrographics Designer file formatCDRCorelDRAW native formatHPGLHP plotter print formatDXFDrawing Exchange Filescreated by Autodesk for AutoCAD

Other Common Vector File FormatsEPSEncapsulated PostScript Filesdeveloped by Adobe Systems for compatibility with PostScript langdevice independentmay contain a TIFF or WMF image for screen presentationAIIllustrator native format

3-D Graphics2D: define shapes by paths3D: define objects by surfacesHierarchical modelingA bicycle consists of a frame, two wheels,

RenderingIn 3D, we have a mathematical model of objects in space, but we need a flat pictureViewpointPosition of cameraScaling with distanceLighting: position, intensity, typeInteraction of light: underwater, smoke-filled roomTexture

RenderingWire frameHidden surface removalSurface propertiesColor and reflectivityLightsShadingA color for each polygonInterpolate color