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Understanding Computer Graphics: Vector and Bitmap Images Explained

This chapter delves into the two main types of computer graphics: vector and bitmap images. Vector graphics are characterized by their mathematical representations of shapes and lines, allowing for scalable and resolution-independent designs. On the other hand, bitmap images rely on an array of pixel values, which can lead to distortions like "jaggies." The process of rasterization interprets vector descriptions for display. We also explore essential tools for creating vector graphics and discuss common file formats used in the industry. This resource is ideal for understanding the foundations of graphics in multimedia systems.

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Understanding Computer Graphics: Vector and Bitmap Images Explained

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  1. SWE 423: Multimedia Systems Chapter 4: 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

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