Introduction to Computer Graphics

• We are going to begin working our way through the book.
  • chapter 1. Is a short introduction.
    • There are many terms introduced.
  • The book is free and on line so there is no excuse not to read it.
• A Pixel or picture element is the basic building block of a digital image.
  • Pixels come from the early days of graphics, the crt
• At one time the "screen" was a phosphor coated piece of glass
  • An electron "gun" would shoot electrons at the screen
  • Which would cause the phosphor to "glow" momentarily
  • And then the screen would need to be refreshed.
  • (LectureLoops.com, but this is a scan from somewhere else)
• There are/were two methods of displaying a scene then.
  • A vector method - where the shape was traced
  • (Hallmark, Think. Make. Share blog)
  • And the raster method.
• The vector method was as close to continuous as you could get.
  • But as the complexity of the scene increases it becomes more difficult.
• The raster method
  • The scene (or screen in this case) was divided into a number of rectangles
  • Each square was given a value of "on" or "off".
  • The electron gun would sweep from top to bottom, from left to right
  • Corresponding pixels on the screen would either be turned on or off.
  • This is a monochrome display.
  • (Again LectureLoops.com)
  • A single gun with multiple levels is gray scale.
  • Three guns with three different phosphor coatings is color.
• The basic mode
  • An array of numbers indicating the intensity of the gun(s)
  • Connected to the guns which translate each "number group" into a beam intensity
  • Which is then displayed.
• By the way, modern LCDs work in a similar manner
  • No electron guns.
  • and all pixels are displayed simultaneously.
• The memory attached to this is called a frame buffer
  • This is probably one of the limiting factors of early displays
  • And is still an item today.
  • But less important than it once was.
• But wait, this can't work
  • Oh Really?
• Modern systems use 24 or higher bit graphics.
  • Each color is given 8 bits or 256 shades of that color.
  • We currently use the colors red, green and blue.
  • Refresh rates are 120Hz and up. (What is a Hz?)
  • And we have many pixels per screen
  • Frequently support two frame buffers
    • One to draw to
    • One to display from.
    • This is called double buffering.
    • This is done automatically in webgl, but not opengl
• The graphics systems we will study will:
  • Specify graphical objects in 2D or 3D continuous space.
  • Then use mathematical transformations to
    • Move these to the proper point of view
    • Project them into two space
  • We will then use algorithms to discrete these items into values in a frame buffer.
• As a side note,
  • most picture formats are raster
  • jpeg, png, ...
  • PGM Reference
  • A PGM Demo
  • But pdf can be vector
  • Many older fonts are raster
  • Most modern fonts are vector
  • STL files (for 3d printing) are vector.
• A demo of scaling in vector vs raster graphics