Graphics File Formats

1
Graphics File Formats
2
Graphics Data

• Vector data
• Lines
• Polygons
• Curves
• Bitmap data
• Array of pixels
• Numerical values corresponding to gray-level or
  color of set of pixels

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Types of Formats

• Bitmap
• TIFF, GIF, JPEG
• Vector
• AutoCAD DXF
• Metafile
• Can contain both bitmap and vector data in the
  same file
• Macintosh PICT

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Types of Formats

• Animation
• TDDD, TTDDD
• Multimedia
• Apple QuickTime
• MPEG

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Types of Formats

• 3D
• Descriptions of shape and color of 3D object
  models (scene elements)
• Models placed in scenes with lights and cameras
• Autodesks DXF
• Used by rendering programs like Autodesks 3D
  Studio

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Types of Formats

• VRML
• Hybrid of 3D graphics and HTML
• Audio
• Video
• Fonts

7
Pixels and Coordinates
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Display

• Fewer colors than device can display

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Display

• More colors than device can display

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Display

• Quantization artifacts
• Banding
• Moire patterns
• New colors not present in image

11
Palettes

• 1-dimensional array of color values
• Color map
• Index map
• Color table
• Look-up table
• Bitmap data in a file stored as series of index
  values
• Pseudo-color storage

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Palettes

• Can easily change, say, all red pixels to green

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Palettes

• Palette element
• 24 or 32 bits
• (0,0,0)
• (255,255,255)
• (255,0,0)
• (0,255,0)
• (0,0,255)
• (255,255,0)
• (0,255,255)
• (255,0,255)

• (128,0,0)
• (0,128,0)
• (0,0,128)
• (128,128,0)
• (0,128,128)
• (128,0,128)
• (128,128,128)
• (255,128,128)

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Palettes

• 320 ? 200 image with 3 bytes of color information
  per pixel and up to 256 colors
• Image without palette would take 3202003 bytes
  of storage, or 192,000 bytes

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Palettes

• 320 ? 200 image with 3 bytes of color information
  per pixel and up to 256 colors
• Image with 1 byte palette would take 3202001
  2563 (length of palette) bytes of storage, or
  64,768 bytes
• For small amounts of data, palette length could
  outweigh savings in color encoding

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Color Spaces

• Composite colors are defined by specifying three
  values for amounts of fundamental colors, or
  color channels
• Color is a point in color space

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Color Spaces

• RGB
• Red, green, and blue
• (R,G,B)
• (0, 0, 0) is black
• (100, 100, 100) is white
• (50, 50, 50) is light gray
• (100, 0, 0) is red
• (0, 100, 0) is green
• (0, 0, 100) is blue

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Color Spaces

• RGB
• 24 bit RGB
• Range is 0-255
• (0, 0, 0) is black
• (255, 255, 255) is white
• (127, 127, 127) is light gray
• (255, 0, 0) is red
• (0, 255, 0) is green
• (0, 0, 255) is blue

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Color Spaces

• Truecolor
• Human eye can distinguish 224 colors
• Device equal to or exceeding this is said to
  display truecolor
• No palette needed
• First byte is R, second byte is G, third byte is
  B

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Color Systems

• Additive color systems
• Adding colors to black creates new colors
• The more colors that are added, the closer to
  white we get
• Presence of all colors creates white, while
  absence of all colors creates black
• Additive color environments are self-luminous
• Color on monitors

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Color Systems

• Subtractive color systems
• Primary colors subtracted (absorbed) from white
  to create new colors (reflected)
• The more colors that are subtracted, the closer
  to black we get
• Presence of all primary colors creates black,
  while absence of all primary colors creates white
• Subtractive color environments are reflective
• Color on paper

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Color Systems

• RGB
• Additive
• Most widely used
• For graphics monitors

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Color Systems

• CMY
• Cyan-Magenta-Yellow
• Subtractive
• Used by most laser and ink-jet printers
• CMYK
• K stands for black, which is treated
  independently
• Glossy magazines
• A dot of composite color is a grouping of four
  dots, each one a CMYK color

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Color Systems

• HSV
• Hue-Saturation-Value
• Hue
• Specifies color
• Saturation
• Called chroma
• Refers to amount of white in a hue
• Fully saturated hue contains no white and is pure
• Red hue with 50 saturation is pink

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Color Systems

• HSV
• Value
• Called brightness
• How much light color emits
• Hue with high value is very bright
• Hue with low value is black
• Color system used by painters
• Add white, black, and gray to pure pigments to
  create tints, shades, and tones

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Color Systems

• HSV
• Tints
• A pure, fully saturated color combined with white
• Shade
• A pure, fully saturated color combined with black
• Tone
• A pure, fully saturated color combined with black
  and white (gray)
• Saturation is the amount of white added
• Value is the amount of black added
• Hue is the color that is added to

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Overlays and Transparency

• Images are often overlaid on live video sources
  at rendering time
• On TV, still images are shown next to live
  talking heads on the news
• Normal images are opaque
• To allow image overlay, some means must exist to
  specify transparency of an image, an image area,
  or an image pixel

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Overlays and Transparency

• Add overlay bit to image pixel value
• When bit is set, rendering application ignores
  those pixel values
• A rendering application can selectively toggle
  overlay bit in all pixel values of a given color
• Person standing in front of a contrasting,
  uniformly colored background screen of a color
  which doesnt appear elsewhere

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Overlays and Transparency

• A rendering application can selectively toggle
  overlay bit in all pixel values of a given color
• Rendering application can toggle overlay bits of
  all pixels of this background color, leaving an
  image of the person cut out from the background
• This cut-out image can be overlaid on any other
  image
• Chromakeying
• 256 levels of transparency

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Bitmap Files

• Image data header information
• Raw format files
• Just image data
• Organization
• Header
• Bitmap data

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Bitmap Files

• Organization
• Header
• Bitmap data
• Footer
• Header
• Palette
• Bitmap data
• Footer

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Bitmap Files

• Organization
• Header
• Bitmap data
• Palette
• Header
• Palette
• Scan line table
• Color correction table (here)
• Bitmap data
• Color correction table (or here)
• Footer

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Bitmap Files

• Organization
• Header
• Palette
• Bitmap index
• Bitmap 1 data
• Bitmap N data
• Footer

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Bitmap Files

• Organization
• Header
• Palette
• Bitmap index
• Palette 1
• Bitmap 1 data
• Palette 2
• Bitmap 2 data
• Palette N
• Bitmap N data
• Footer

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Bitmap Files

• Header
• Binary or ASCII data
• Composed of fixed fields
• Format of header varies
• Types of fields
• File identifier
• File version
• Number of lines per image
• Number of pixels per line

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Bitmap Files

• Header
• Types of fields
• Number of bits per pixel
• Number of color planes
• Compression type
• X-origin of image
• Y-origin of image
• Text description
• Unused space

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Bitmap

• Header
• File identifier
• Unique identifier which identifies the format
• GIF
• File version
• For GIF, 87a or 89a
• Number of lines per image
• Image length
• Image height
• Number of scan lines

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Bitmap

• Header
• Number of pixels per line
• Image width
• Scan line width
• Number of bits per pixel
• Per color plane
• Number of bytes per pixel is pixel depth
• X and Y origins
• Indicates where image lies on output device

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Color Correction Table

• Information to help rendering application in
  displaying an image on a device different from
  the one assumed by the creator application

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Scan-Line Table

• An array of offset values used to index the
  location of each scan line
• Each offset value indicates the starting position
  of each scan line