CSCI220 Multimedia Literacy

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CSCI220 Multimedia Literacy

• Digital Imaging

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Graphics

• A Picture is Worth 1k Words
• We are a visual society
• Cave drawings before writing
• Kids learn from pictures before text
• Business information full of graphics and images

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Two Graphic Classes

• Natural digitized form of analogue image
• Artificial graphics, created by hand or
  computer process

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Graphic use in Multimedia

• Backgrounds
• Buttons
• Icons
• Navigation
• Colors
• Maps

• Charts
• Explaining concepts
• Creating mood
• Corporate logo
• Etc

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Image Types

• Line Art only Black and White pixels
• Flat colors
• Grayscale 256 levels of gray shades
• BWG
• Color
• 4-bit (16 colors)
• 24-bit (16 million colors)

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Image Quality

• Resolution as related to graphics (different from
  monitor or sound resolution)
• Image resolution amount of information ( of
  pixels) stored for each image.
• Measured in ppi (pixels per inch)

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Making Pictures with Numbers

• Computer represents all things with numbers
• Images as well
• Analytic geometry cartesian coordinates
• Coordinate describes location of a point (board
  image)
• Create a line or curve as a set of points.
• Points close together look solid
• Pixel picture element all these points
• Store location and attributes (b or w, 1 or 0)

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Bitmapped/Raster Graphics

• Graphic file stores location and value of each
  pixel
• (Board image - bitplane)
• Simple bw uses only 1 bit plane only 2 values
  (black or white)
• Greyscale 16 shades ranging from b to w
• 16 values cant store as 0 or 1
• Each value needs 4 bits (1001, 1011)
• Needs 4 bit planes (board image)

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Bitmapped/Raster Graphics

• Bitmapped color works the same way
• Color shades represented by different RGB values
• 256 shades of RGB, needs 8 bit planes
• i.e. 10111001 one shade of blue
• 3 primary colors need to represent value of
  each
• 3 x 8 24 bitplanes 24 bit color

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Vector Graphics

• Resolution Independent
• Instead of storing each pixel (large file), use
  mathematical equations to represent lines and
  curves

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Graphic File Storage Types

• TIFF Tagged Image File Format
• Bit mapped, widely used
• Bit depths up to 32 bits
• Used by multiple platforms
• Compression available

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Graphic File Storage Types

• GIF Graphic Interchange Format
• Developed by compuserv
• Limited number of colors (256) smaller files
• Popular on the Web
• Transparent gif background rendered invisible
  through masking
• Interlaced gif stored and transmitted in layers
  makes for fast loading on web sites

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Graphic File Storage Types

• PNG Portable Network Graphics
• Next generation web graphic NOT!
• Advanced features of gif feathered transparency
• JPEG Joint Photographic Experts Group
• Bitmapped
• More colors than gif better for photos

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Graphic File Storage Types

• BMP bitmap
• Windows standard
• Also WMP, PICT, PCX, CGM, EPS, DXF, QT, AVI, etc

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Digital Images

• Picture Resolution defined by of pixels in
  image
• Written as product of images dimensions
• Aspect Ratio num of horizontal pixels / num of
  vertical pixels
• When resizing or resampling, try to preserve this
  to prevent distortion
• 320 x 200 (1.61) low resolution
• 640 x 480 (1.331) medium resolution
• 1024 x 768 (1.331) high resolution

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Digital Images

• Resolution has effect on image quality

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Digital Images

• Black and White images
• Dynamic Range determined by bitdepth
• Range of values used to represent the image
• i.e. 16 value greyscale vs 256 value greyscale
• Next image displays
• (a) 256 levels (b) 16 levels
• (c) 4 levels (d) 2 levels (halftone screening)

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Color Images Color Systems

• RGB divides into 3 channels red, blue, green
• Channel component of an image that may be
  manipulated separately
• Colors defined by values of r, b, and g

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Color Images Color Systems

• RGB Color Space
• At Origin RGB 0, 0, 0 Black, no color
• At point RBG 1, 1, 1 White
• 1, 0, 0 Red
• 0, 1, 0 Green
• 0, 0, 1 Blue
• Major hues Magenta (1, 0, 1), etc
• IMPORTANT to reduce amount of magenta in an
  image, add green opposite color

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Color Images Color Systems

• CMY based on values of Cyan, Magenta, Yellow
• Used in print media
• CMY color space
• 0, 0, 0 no color achromatic white
• 1, 1, 1 - black

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Color Images Color Systems

• CMYK adds fourth channel - black

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Color Images Color Systems

• HSB Hues, Brightness, Saturation
• Hues spectral colors arranged on standard color
  wheel
• Brightness relative lightness or darkness of
  shade
• Saturation purity or strength of hue
• Unsaturated no hue white
• Partially Saturated pastels
• Deeply Saturated bright vivid colors

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