Computer Graphics

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Computer Graphics
representation

• description of objects
• (creation of models)

image
image processing
reconstruction
simulation
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Description of an image
vector image a set of objects

• raster (bitmap)
• image an array of points

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I/O Devices

• Output devices
• raster predominate display (800 ? 600, 1024
  ? 768, 1280 ? 1024) ink and laser printers
  (300 dpi, 600 dpi) ink plotter
• vector pen plotter
• Input raster device for reading an
  image scanner
• digital camera

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Bitmapped Image

• points (so-called pixels picture elements)
  arranged in a rectangular array
• the only attribute of a pixel is the colour b/w
  (monochromatic) 1 pixel ? 1 bit 16 colours 1
  pixel ? 4 bits 256 colours 1 pixel ? 8 bits 224
  colours (true colour) 1 pixel ? 3 bytes
• the number of bits required for one pixel ?
  colour depth
• the only thing possible to change colour

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Vector Images

• a set of objects (lines, arcs, circles etc.)
• shapes are described in mathematical terms
• objects have various properties (position,
  size, colour, type of line etc.)
• objects properties can be changed easy

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Colour Models

• are given by basic colours, rules for mixing of
  colours and by rules for changing other features

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RGB

• the so-called additive model
• colours are added to the black one
• adding colours forms a lighter colour
• white all colours black no colour
• outside light is not necessary

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CMY

• the so-called subtractive model
• colours are subtracted from the white one
• adding colours forms a darker colour
• white no colour black all colours
• outside light is necessary (the light is
  reflected from colour pigments)

• in practise the model CMYK (K black) is used

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Model HSVHue , Saturation , Value

• hue basic spectral colours values are
  declared in degrees (0360)
• saturation the ratio of pure colour and white
  (100 spectral colours)
• value brightnessthe high colour (100 ) has no
  touch of black decrease of brightness ? adding
  black
• new colours are created by adding black and white
  to spectral colours

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Colour Palette

• (Colour look-up table)

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PaletteColour Look-Up Table

• defines how many and which colours are used in
  the image
• colour of a pixel can be done either by values of
  primary components or by a number pointing to the
  look-up table of colours
• criterion for using palette required room in the
  storage
• palette is used for 256 colours
• palette is not used for true colours
• advantage colours in the image can be changed
  easy by changing the palette

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• Uniform palette (256 colours)
• 3 3 2 

Other example of palette 7 x 12 x 3 7 shades of
red, 12 shades of green a 3 shades of blue (252
colours)
Adjusted colour palette  palette optimised for
one specific image
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Example of a Usage of Palettes
origin picture 24 bits per pixel
palette 16 colours 4 bits per pixel
palette 256 colours 8 bits per pixel
adjusted palette 256 colours 8 bits per pixel
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Graphic Editors
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Bitmap Editors (Paint Programs)

• creation and modification of bitmaps
• drawing and modifications change of a colour of
  pixels
• Examples
• Paint, Corel Photo-Paint, Adobe Photo Shop
• Image Composer, Photo Styler, Photo Finish etc.

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Tools of editors enabling drawing

• setting of drawing colour, background colour,
• thickness of lines
• filling with various colours and patterns
• copying, movement, rotation, mirroring of a
  cut-out

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Tools in editors oriented on modification of
images (e.g.. photographs) enable

• modification of colours
• change of a palette
• modification of brightness and contrast
• retouching tools sharpening, blurring
• impression of a pattern and other effects

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Vector Graphics Programs(Draw Programs)

• drawing creation of objects
• modification change of objects properties

division from the viewpoint on specialization
in drawing, graphics e.g.. Corel Draw,
Adobe Illustrator in technical drawing CAD
systems e.g.. AutoCAD, Microstation,
Spirit from the viewpoint on 3D drawing 2D
programs 3D programs
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Ability of editors oriented on drawing

• drawing basic geometric objects and text
• setting of lines properties (colour, thickness,
  type) and fills (colour, pattern, texture, a
  progression between two colours)
• selection of drawn objects
• manipulation with selected objects copying,
  movement, rotation, mirroring, change of
  size grouping, ordering, aligning, modification
  of curves
• effects adding perspective, envelope, blending
  objects, extruding objects, Power Clip, using
  lenses

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blending
Power Clip
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Properties of CAD systems(Computer Aided Design)

• precise specification of a point
• drawing lines, curves, basic geometric objects,
  text and hatch
• selection of drawn objects
• a great power to modify objects copying,
  movement, rotation, mirroring, change of
  size, trim, extension, ...
• dimensioning
• layers
• possibility to join the drawing to a database,
  libraries of elements

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Editors enabling 3D drawing

• drawing 3D objects and operations with them
  (union, intersection, subtraction)
• visibility

• shading, casting of a shade

• setting of materials
• properties colour, smoothness, metallic look,
  shine etc.
• rendering creation of a real 3D image from a
  computer designed model

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Prostorový model
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Druhy osvetlení
point light
distant light
spot light
distant light
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Render
Rendering
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Graphics File Formats
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Bitmapped Formats

• store image as an array of pixels
• built-in compression
• file consists of
• header information about the image
• identification of the format, width and
  height of the picture, colour depth etc.
• definition of the palette
• data information about pixels colour(values
  of components or index into the palette)

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Bitmapped Formats

• the most widespread
• GIF, JPEG, BMP, TIFF, PCX
• advantages
• are easy created from data in memory
• are easy transport to a raster output device
• disadvantages
• require a lot memory
• a picture cannot be enlarged or reduced without
  losing quality

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Vector Formats

• include a description of objects creating the
  image
• individual formats have different purpose and
  are very different
• file consists of header vector data
• the most widespread CDR (CorelDraw) PLT, HPG
  (language HPGL, description for output
  devise) DWG (AutoCAD) DXF, DXB (AutoCAD)

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Vector Formats

• advantages
• size of a file is proportional to a complexity of
  the image
• a picture can be enlarged or reduced without
  losing quality
• can be easy adjusted to an output device
• some formats are saved as an ASCII text, so they
  can be processed by various ways
• disadvantages
• are not uniform
• must be transformed for output devices

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Metafiles

• include both raster and vector data
• individual formats are very different
• designed for exchanging graphical data between
  different application programs
• the most widespread WMF EPS (language
  PostScript, for print)