Week 6 Lecture slides

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Cosc 1P02

• Week 6 Lecture slides

"To succeed, jump as quickly at opportunities as
you do at conclusions." --Benjamin Franklin
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Light

• Light is electromagnetic radiation and has
  properties of both waves and particles
• Human perception of light
• the visible light spectrum has wavelength of
  370-730 nanommeters (nm, 10-9, 0.00000037-0.000000
  73 meters)
• low acuity
• cannot distinguish fine detail
• TV screen, monitor, photographs actually contain
  many dots but we see a clear picture

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Color

• Different wavelengths of visible spectrum are
  sensed as different colors
• ROYGBIV
• Eyes have 3 sensors that trigger at different
  wavelengths
• 425 nm (blue)
• 550 nm (green)
• 560 nm (red)
• Brain interprets the values registered by the
  three censors as colour.
• each sensor registers something at all
  wavelengths
• highest value for wavelength closest to trigger
  wavelength
• brightness (luminance) handled separately from
  colour

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Electro MagneticSpectrum
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Picture Representation

• Picture represented by a series of dots (pixels
  picture elements)
• if small enough eye wont detect
• pictures are two-dimensional
• pixels arranged in rows and columns
• e.g. monitor resolution (1024x768)
• Can trick brain into seeing colour by providing 3
  sources of light
• e.g. orange light
• actual wavelength will cause the brain to get a
  value for blue, green and red from the sensors
• if transmit 3 colours (blue, green, red) in close
  proximity that trigger the 3 sensors at orange
  level, will see orange
• Each pixel is really 3 dots red, green and blue
  (RGB)
• the amount (intensity) of each colour dot varied
  to produce the colours
• e.g. blue at high intensity and others at low
  intensity will be seen as blue

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Encoding (Digitizing) Pictures

• Picture is a collection of pixels
• width height
• Each pixel has three Color values
• red (R), green (G) and blue (B)
• represent the intensity of the light of that
  color
• 1 byte gives 256 different intensities for each
  color
• 3 bytes or 224 16,777,216 different colors
• Digital camera
• array of sensors (3 per pixel) pick up R, G and B
  (like eye)
• 3 values (bytes) recorded per pixel
• e.g. 10 megapixel camera
• 3648 x 2726 9,980,928 pixels
• at 3 bytes per pixel 29,942,784 bytes or
  approximately 28Mb per picture

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Simplest Representation
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Colour Representation
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Exploring Pictures

• PictureInspector tool
• Java program built using BasicIO Media
  libraries
• displays picture and allows zooming on a portion
• E.g.
• beach.jpg
• Coordinate system
• picture has width height (in pixels)
• top left corner is (0,0)
• x-coordinate is column
• y-coordinate is row
• RGB values

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Picture and PictureDisplayer

• Picture
• class in Media library
• access to attributes and pixels of picture
• pictures can be loaded from a file (.jpg)
• PictureDisplayer
• class in BasicIO library
• provides a window on which a picture can be
  displayed
• picture objects placed on PictureDisplayer
• E.g. load and display a picture

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Picture Methods
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PictureDisplayer Methods
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Choosing a Color

• Set color of each pixel
• Sequence through all pixels
• Picture is a collection
• for-each
• ASCIIPrompter to get RGB values
• Pixel class
• methods to get set color of pixels
• Example
• Color constructor allows setting RGB
• Black white
• Gray
• if RGB we get gray
• different shades with different intensities

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Pixel Methods
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Grayscale

• Convert a picture into grayscale
• essentially what we call a black and white
  picture
• shades of gray indicating the luminance of the
  picture
• Gray if RGB
• set RGB to same value
• average of RGB values
• Color methods
• Example
• Note method may change the pixels of the color
  parameter
• they stay changed
• just like a method moving a turtle changes its
  position

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Color Methods
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The end