Graphics: Creating Images

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Graphics Creating Images

• Chapter 8,
• Exploring the Digital Domain

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In this chapter . . .
You will learn about

• how the computer creates, stores, and displays
  images
• how painting programs allow the user to control
  graphic primitives
• the features that are found in drawing and
  illustration programs
• how software helps to automate creating 3-D
  projections and animations

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Graphic images

• (for display) graphic images are composed of
  pixels
• this type of graphic is called bit-mapped or
  raster graphics
• the image is stored as a sequence of bits
  (bottom) representing the pixel properties (top)

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Graphic Images

• in most bit-mapped images, each pixel requires a
  sequence of feature bits
• the number of bits needed corresponds to the
  bitplanes for the image

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Graphic Images

• vector graphics or object-oriented treat the
  image as a collection of graphic objects such as
  lines, curves, and figures defined mathematically
• vector graphics are resolution independent and
  scalable
• vector graphics are more easily edited and often
  more compact in storage
• vector graphic images must often be converted to
  bitmapped images for display

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Graphic Applications
Bit-mapped graphics
Vector graphics

• drawing programs
• illustration programs
• 3-D modeling and rendering programs

• painting programs

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Storing Graphic Images

• TIFFs, GIFs, PNGs, BMPs, WMFs, and PICTs are
  image file formats used to store graphic images
  too.
• PCX, CGM, EPS, EMF, DXF, SVG, and QuickTime are
  also popular formats

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Storing Graphic Images

• PCX is the native file format for PC Paintbrush
  and other Windows apps
• CGM (computer graphics metafile) is an
  open-source metafile format
• EPS (encapsulated PostScript) is a standard
  metafile format for professional printing
  applications

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Storing Graphic Images

• EMF (enhanced metafile format) is Windows
  successor to WMF
• DXF (drawing exchange format) is AutoCads 3-D
  file format
• SVG (scalable vector graphics) is an open-source
  format based on XML
• QuickTime is used for storing video and animations

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Painting Programs

• two-dimensional, bitmapped images/ files
• interface based on artwork metaphor
• image (canvas) painted with brushes, pencils,
  chalk, etc.
• colors, patterns, and textures selected from
  palettes
• image is divided into foreground and background
  layers

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Painting Programs

• tools are based on selecting areas of pixels for
  editing
• masks can be used to separate sections of the
  image
• multiple layers may also be used

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Painting Programs

• offer a variety of patterns, textures, and colors
• have assorted tools for transforming selected
  portions of the image
• have tools for creating pixel masks

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Vector Graphics

• the image is composed of graphic objects (lines,
  curves, figures, etc.)
• each object is defined by its graphic properties
• these properties may be changed and scaled easily

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Vector Graphics

• employ anti-aliasing or smoothing to reduce
  jagged artifacts
• are easily scalable for a variety of resolutions
  and output devices

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Vector Graphics

• incorporate parametric curves--based on
  mathematical plotting
• for examples, Bezier and B-spline curves

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Vector Graphics

• each object occupies a separate layer
• layers may be moved, scaled, and arranged in
  different orders
• objects may be deleted and inserted easily

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Drawing Programs

• are simple vector graphic programs
• best-suited for basic illustrations
• employ an artwork metaphor for the user interface
  like painting programs
• an image is a set of graphic objects that are
  created individually and composed together

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Illustration Programs

• are also vector graphic programs
• generate PostScript (scalable) output
• have extensive tools, effects, and features
• used for professional applications

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3-D Graphics

• 3-D graphic programs automate creating images
  with perspective projection and special effects
  of lighting and shading
• these applications employ either volume-based or
  surface-based 3-D graphics

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3-D Graphics
volume-based
surface-based

• 3-D image is defined by voxels
• 3-D picture elements having location, color,
  intensity, transparency, opacity
• used for scientific visualization and modeling

• 3-D image is composed of objects defined in 3
  dimensions
• regular shapes form the facets or components of
  each object
• rendering involves adding texture, shading, and
  lighting effects

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Surface-based 3-D Graphics
3-D image is created in stages

• model description
• each object is defined in 3 dimensions
• scene description
• objects are placed in scene
• rendering
• perspective, and special effects added

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Surface-based 3-D Graphics

• SOLID MODELING--objects are composed of simple
  3-D regular solids used as primitive
• POLYGON-SURFACE MODELING--objects are composed of
  facets shaped from polygons
• WIREFRAME MODELING--objects are composed of
  facets including parametric curved shapes

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Surface-based 3-D Graphics
RENDERING TECHNIQUES

• Lambert shading
• Gouraud shading
• Phong shading
• Ray-tracing

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Animation

• animations are composed of individual graphic
  images called frames
• frames are displayed at a rate fast enough to be
  perceived as continuous motion
• animation software help to automate the creation
  of animated graphics

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Animation

• In-betweening automates the creation of animated
  sequences
• key frames are defined for starting and stopping
  positions
• the software calculates the incremental frames