CG_Chapter3

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Chapter3 Raster Image

Pixel is short for picture element
A raster images is simply a 2D array that stores the pixel value for each pixel
image pixels != display pixel

3.1 Raster Devices

  • Output
    • Display
      • Transmissive: liquid crystal display LCD
      • Emissive: light-emitting diode LED display
    • Hardcopy
      • Binary: link-jet printer
      • Continuous tone: dye sublimation printer
        thermal dye transfer donor ribbon continous tone
        ppi: pixel per inch
        dpi: dots per inch
        stair stepping
  • input
    • 2D array sensor: digital camera
      CCD: charge-coupled devices
      CMONS: complimentary metal-oxide-semiconductor
    • 1D array sensor: flatbed scanner

3.2 Images, Pixels, Geometry

$I(x,y): R \to V$
$R \subset \mathbb{R^2}$ is a rectangular area and $V$ is the set of possible pixel values

3.2.2 Monitor intensities and Gamma

  • monitors are nonlinear with respect to input
    displayed intensity = (maximum intensity)$a^\gamma$
    a in the input pixel value between 1 and 0
    describing a display’s nonlinearity using $\gamma$ is only an approximation

    3.3 RGB Color

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    black = (0, 0, 0)
    red = (1, 0, 0)
    green = (0, 1, 0)
    blue = (0, 0, 1)
    yellow = (1, 1, 0)
    magenta = (1, 0, 1)
    cyan = (0, 1, 1)
    white = (1, 1, 1)

3.4 Alpha Compositing

pixel coverage $\alpha$ fraction of pixel covered by the foreground layer
$c = \alpha c_f + (1-\alpha)c_b$
alpha mask alpha channel

  • Image Storage
    jpeg: lossy
    tiff: lossless
    ppm: lossless
    png: lossless