Digital Media

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Digital Media

• Dr. Jim Rowan
• ITEC 2110
• Images Chapters 3, 4 5

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Images Chapters 3, 4 5

• In the next several lectures we will be covering
  these topics
• Vector graphics
• Bitmapped graphics
• Color
• It will be presented in this order
• Bitmapped graphics
• Vector graphics part 1
• Color parts 1 2
• Vector graphics part 2 3D

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Computer Graphics...

• A very different viewing media than print
• Usually consumed on a fairly low resolution
  monitor
• Forcing us to look carefully at the processes
  that move stuff from the real world to the
  computer... AND BACK!
• Graphic images work very differently on a screen
  than when in print
• can be seen with lights out
• will be viewed from different resolution monitors
• viewing angles are different
• reflections off screen

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Computer Graphics

• Computer graphics on the Internet
• fostered the shift away from print based media
• has begun to develop its own visual vocabulary
• Inside the computer theres a numeric model of a
  real-world phenomenon
• Two ways to model computer graphics (images)
• bitmapped images
• vector graphics
• each with their advantages and disadvantages

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The way you display data affects how it is
understood

• This is a field of study all by itself that
  includes computer graphics, cognitive science and
  psychology
• The way data is displayed affects how people
  interpret the data
• how color is used
• the numeric scales used
• Different graphing forms emphasize different
  aspects of the numbers
• pie charts
• bar charts
• line graphs

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Designing information display

• How to lie with statistics
• Edward Tufte, Yale University
• Visual Display of Quantitative Information
• Envisioning Information
• Visual Explanations

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Computer Display types

• Now... all are rectangular arrays of pixels
• Not always that way
• Early graphics (1976) used a steerable electron
  gun, not raster graphics
• Since then...
• we have moved away from electron gun

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Internal and External graphics models

• Internally an application keeps a numeric model
• Inside a computer its all numbers
• To display the internal model so we can see it,
  an application must project this internal model
  onto a display
• The internal model, the numbers, are in the
  computer
• This process of projecting this model onto a
  display is called rendering

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Two approaches to internal graphic modeling

• Why two approaches?
• drastic filesize differences
• each is good for its type of image
• each has its own unique advantagess
• Bitmapped graphics
• grandfathered name... more like pixel mapped
  graphics
• Vector graphics
• Its more like object graphics because you
  describe objects using vectors (formulas)

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With bitmapped graphics...

• There are logical and physical pixels
• images are modeled internally as an array of
  pixel values... the logical pixels
• physical pixels are the actual dots on screen
• Moving from logical and physical pixels
• called rendering
• may be different size, shape and different
  resolution
• will probably require clipping and scaling to
  move from logical to physical pixels
• for example

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00011000000011110000010110100000111100000001100000
A true bitmapped image is black and white Each
logical pixel is represented by a single bit
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When color came along it borrowed the
idea... except that each logical pixel became a 3
byte RGB color specification instead of a single
bit
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1111 1111 . 1111 1111 . 1111 1111 1111 1111 .
1111 1111 . 1111 1111 1111 1111 . 1111 1111 .
1111 1111 0000 0000 . 0000 0000 . 1111 1111 0000
0000 . 0000 0000 . 1111 1111 1111 1111 . 1111
1111 . 1111 1111 1111 1111 . 1111 1111 . 1111
1111 1111 1111 . 1111 1111 . 1111 1111 1111 1111
. 1111 1111 . 1111 1111 1111 1111 . 1111 1111 .
1111 1111 1111 1111 . 1111 1111 . 1111 1111 1111
1111 . 1111 1111 . 1111 1111 0000 0000 . 0000
0000 . 1111 1111 0000 0000 . 0000 0000 . 1111
1111 0000 0000 . 0000 0000 . 1111 1111 0000 0000
. 0000 0000 . 1111 1111 1111 1111 . 1111 1111 .
1111 1111 1111 1111 . 1111 1111 . 1111 1111 1111
1111 . 1111 1111 . 1111 1111 1111 1111 . 1111
1111 . 1111 1111 1111 1111 . 1111 1111 . 1111
1111 0000 0000 . 0000 0000 . 1111 1111 1111 1111
. 0000 0000 . 0000 0000 0000 0000 . 0000 0000 .
1111 1111 0000 0000 . 0000 0000 . 1111 1111 1111
1111 . 0000 0000 . 0000 0000 0000 0000 . 0000
0000 . 1111 1111 ... for 1080 more bits... 1111
1111 . 1111 1111 . 1111
255 255 255 255 255 255 255 255 255 0 0 255 0 0 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255
255 255 255 255 255 255 0 0 255 0 0 255 0 0 255 0 0 255 255 255 255 255 255 255 255 255 255 255 255 255
255 255 255 0 0 255 255 0 0 0 0 255 0 0 255 2550 0 0 0 255 255 255 255 255 255 255 255 255 255
255 255 255 255 255 255 0 0 255 0 0 255 0 0 255 0 0 255 255 255 255 255 255 255 255 255 255 255 255 255
255 255 255 255 255 255 255 255 255 0 0 255 0 0 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255
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72 bits in the color table 100 bits in the pixel
map 172 bits total Question With 2 bits
encoding the color, if we expanded the color
table, how many colors could be represented?
255 255 255 0 0 255 255 0 0
00 00 00 01 01 00 00 00 00 00
00 00 01 01 01 01 00 00 00 00
00 01 10 01 01 10 01 00 00 00
00 00 01 01 01 01 00 00 00 00
00 00 00 01 01 00 00 00 00 00
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Vector graphics

• Internal model is very different than bitmapped
  graphics
• Images are described as mathematical equations
• Rendering is very different
• must translate EQUATIONS to physical pixels
• Simple to clip or scale
• must compute the array of physical pixels from
  the equations

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vector graphic
bitmapped graphic
Here are two images, blue squares Both are
displayed at 72 pixels per inch Both are
displayed as 1024 X 1024 pixels in size Each with
3 byte (24 bit, millions of colors) color
encoding Which would have the larger (in terms of
file size) internal model? Why?
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vector graphic
bitmapped graphic
Here are two more complex images Both are
displayed at 72 pixels per inch Both are
displayed as 318 X 318 pixels in size Each with 3
byte (24 bit, millions of colors) color
encoding Which would have the larger (in terms of
file size) internal model? Why?
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Bitmapped/Vector Graphics

• Bitmapped image file size is
• affected by dimensions, resolution and color
  resolution
• not affected by contents
• Vector graphics file size is
• affected by the contents of the image
• the more complex, the larger the file gets
• size of the file is not affected by resolution

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Bitmapped/Vector Graphics

• Access to objects found in the image
• vector is easy, objects are described by
  mathematical equations
• bitmapped, no objects, just pixels this is very
  difficult
• Special effect (like blur, which requires access
  to surrounding pixels) differences
• Bitmapped?
• Easy the pixels are stored in the model
• Vector?
• Not so much
• First convert to bitmapped, then blur

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Bitmapped/Vector Graphics

• Scaling and Resize
• Vector? Simple... change formula
• Changes can be made BEFORE pixel values are
  calculated
• Bitmapped? Complicated...
• frequently results in artifacts
• Why is bitmapped scaling and resizing
  complicated? gt

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Original image 10 x 5 Now make it twice as
big Draw on image















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• Original image 10 x 5
• Draw on image
• Now make it twice as big
• What happens if there are
• two colors next to one
• another?
• Strictly duplicate?
• jagged edges
• Interpolate them?

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Original image 10 x 5 To make it 50
larger... What do you do? Do you make it 15 x
7? or 15 x 8? 1 pixel gt 1? 2? There is no such
thing as 1.5 pixels...












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Bitmapped ltgt Vector

• Vector can more easily be converted to
  bitmapped...
• in fact, this process already exists since you
  must RENDER vectors to display them.
• Bitmapped to vector is complicated
• Vector is based on shapes but bitmapped does not
  define any shapes
• Software must identify edges and find the shapes.

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BitmappedImage Manipulation

• Why?
• Correct deficiencies (i.e. flash red eye)
• encapsulated sequence of operations to perform a
  particular change
• Create images that are difficult or impossible to
  create in nature
• special effects

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Image layers

• Both bitmapped and vector graphics use layers as
  an organizational device
• In bitmapped graphics
• layers are used like digital tracing paper to
  isolate objects in the image
• colors can be separated and manipulated
  individually

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Image Manipulation Tools

• Selection tools
• for regular shapes
• rectangular and elliptical marquee tools
• why is it called marquee?
• for irregular shapes
• lasso (polygon, magnetic, magic wand...)
• magnetic snaps to an enclosed object using
  edge-detection routines

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Selection tools...

• Allow the application of filters to only the
  selected parts of the image
• The unaffected area is called a mask... can be
  thought of as a stencil
• A 1-bit mask is either transparent or opaque
• An 8-bit mask allows 256 levels of
  transparency... AKA alpha channel

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Selection tools...

• Making the mask with a gradient produces a softer
  transition... a feathered edge.
• Can use anti-aliasing along the edge more
  effectively hides the hard edge visually
• Layers can have masks associated with them
• Allows interesting compositing of image parts

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Show Image testPageImage.tiff

• 2272 pixels wide
• 2868 pixels tall
• RGB encoded
• No compression
• No table
• How Big?

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Show Image testPageImage.tiff

• Inspect it with mac cmd-I
• Open image with hexFiend
• How big is it?
• What is in it?
• Mostly FF... why?

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HMMMMMmmm

• Well talk more about this size issue later when
  we discuss bitmapped graphics in more detail
• We will also consider compression techniques
  other than the table method

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Record a Demo

• Vector graphics using Inkscape

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Questions?