Some notes from chapter 1.

• Images
  • In the "real world" we have a single "viewer"
    • This is the position where the image is formed.
    • Think of this as a camera or your eye.
  • We also have multiple physical objects
    • Physical
  • In the graphics world, we replace the objects with
    • Triangles - as often as we can,
    • Vertices
      • A line consists of two of these.
      • A circle one of these and a diameter
  • We generally employ a graphics pipeline to transform from the "vertex" description of the scene to the picture on the screen.
    • Our current project somewhat violates that
      • We are thinking less of modeling the image than we art of "painting" it.
      • Do we have the ability to look from other locations?
      • Zoom in?
      • We will need to separate the model from the display, but that is about it.
• Light and Images
  • In the real world light sources are actual sources of light.
    • Either natural or artificial they have a position.
    • And they emit photons (light) that strike the objects illuminating them.
    • Light is then "blocked" and does not illuminate the items behind the first object.
  • Or light is a wave
    • These waves are at different frequencies.
    • The frequencies correspond to the "color" of light.
    • Which corresponds to part of the color that is used to illuminate the object.
  • In either case, it is useful to think of what we see of the object is the light that is "bounced off" of the object.
    • A stealth object absorbs all light that strikes it.
    • Thus there is nothing to see.
    • A red object absorb es all but the red light, which bounces off.
  • In the graphics world
    • We need to model this entire process.
    • Lights are assigned properties such as
      • Color emitted
      • Strength or attenuation
      • Possibly direction
    • We need to "model" how this light interacts with surfaces
      • Does the light reach the surface or is is blocked by another surface?
      • Is the light reflected from the surface?
      • Is the light transmitted through the surface?
  • One way to think of this is pictured in figure 1.11 p 14.
    • This is not a practical approach, there are infinitely many rays coming from from the light source.
    • But the inverse of the picture, ray tracing
    • Another technique radiosity which models a heat transfer technique.
    • Traditional rendering
      • At each pixel compute the color contributed from each light source.
      • This makes shadows and reflections problematic.
      • But is reasonably fast.
• Imaging systems.
  • Consider a pin hole camera
    • A box with a very small (pin hole) in one end.
      • This is so small only a single ray of light can "travel" through it.
    • A photographic plate is on the other end.
    • In this case we assume that light is "emitted" from objects in the scene.
    • Light travels from the object, through the hole and strikes the plate.
    • 
    • Important here
      • The distance d to the image is fixed in the camera.
      • The object location (x,y,z) is fixed as well.
      • In the image we are looking along the x axis.
    • As we move the object, we find distant objects "move" to the center.
    • 
    • in any case, we can compute the point (x',y',z') using geometry
      • This point is called the projection point
      • (x,y,z) -> (-x/(z/d), -y/(z/d), -d)
    • Several definitions
      • θ = 2 tan^-1(h/(2d))
        • This defines the field of view for the camera
        • 
        • This is some way defines the view frustum , With no front plane.
        • Or a view pyramid.
        • Later we will define a front clipping plane
      • This camera has infinate "depth of field"
        • Later we will define a back plane, to have a true veiw frustum
      • This camera has no adjustments
        • We will look at other camera models where this is addresed.
        • And we can do all kinds of cool things digitally to mess with the image as well.
      • Generally we work with a camera with a focal plane in front of the camera.