Download Lecture 24

Design Realization
lecture 24
John Canny
11/18/03
Last time
 Simulation in Matlab/Simulink
 PID stabilization
 Automatic code generation - example
This time
 Improvisation: application to circuits and realtime programming.
 Optics: physics of light.
Improvisation
 Exploration of the design possibilities of a
medium.
 Earlier we listed “qualities” of media.
 For technical media, list their capabilities.
 E.g. speed, complexity, cost, reliability,… for a
system: network, processor, sensor etc…
Improvisation – extreme designs
 Trying to achieve a design goal using “extreme”
designs:
 E.g. expressive animation using motion only, or
using high-performance characters.
 Mood change using lighting only, or camera position.
 Chair designs: very light/heavy, simple/complex,
single material or form…
Improvisation – extreme designs
 Technical media:
 Recognition with one type of sensor (e.g. light).
 Complex control with many simple chips (e.g. PICs),
or with one complex chip (or a PC).
 Communication with simple network (serial) vs. a
stack such as ethernet or bluetooth.
 PC board layout: all surface-mount components,
one-sided vs. two-sided layout, high vs. low density.
Improvisation – pattern libraries
 Normally, you learn a new medium by finding
and applying design patterns.
 Application notes for PICs, sample circuit boards.
 As you become accomplished, you should save
your own design patterns somewhere.
Improvisation: challenging conventions
 Design patterns are a good way to learn, but
conventions should be challenged regularly.
 This involves understanding the essential
functionality of components, e.g.
 RS485 transceivers as multidrop bus drivers.
 Battery sensors as A/D converters.
 Once this is understood, you’re free to design
“out of the box”.
Break
Why Optics?
 Most of our interaction with technology is
visual: computers, architecture, games
 Most of the media we consume are visual: TV
movies, newspaper*, DVDs,…
 There are many new component-ized optical
technologies, and the design possibilities are
excellent.
Optics – physics of light
 Light is electro-magnetic
radiation with wavelengths
from 400-700 nm.
 Longer wavelengths at the
red end of the spectrum,
grading to violet at the
short end.
Optics – physics of light
 The eye contains two kinds of light-receptive
cell called rods and cones.
 Cones are the
color sensors:
 The three types
allow the eye to
respond to threeway color mixes.
Additive color mixes
 Because of the 3 types of receptor, colors can
be synthesized using 3 colored emitters:
 Phosphors (in TV and CRT displays)
 White light with filters (LCD displays, projectors)
 LED displays
Color Bases - XYZ
 To describe color, its convenient to define a
different basis.
 The XYZ (CIE) basis uses X,Y coordinates to
represent color, and Z to represent brightness.
 Allows colors to be plotted in 2D.
 They are related to R,G,B by a linear
transformation:
[R] = [ 2.739 -1.145 -0.424 ] [X]
[G] = [ -1.119 2.029 0.033 ] [Y]
[B] = [ 0.138 -0.333 1.105 ] [Z]
CIE plot
 Shows colors in XY coordinates.
 Saturated (full) colors
at the boundary.
 Light sources cover
regions in the plot.
 Blended colors are
in the convex hull
of the source.
 (Line shows black
body radiation color)
HSV
 Another common basis is HSV (Hue,
Saturation, Value).
 Hue is taken to be the angle of the color.
 Saturation is the
distance from the
vertical axis.
 Value is the height
(brightness).
 Considered more
intuitive for color choice.
YUV
 The last common basis is YUV (popular in
cameras and digital images).
 Y is intensity, U,V encode color (can be
negative).
 Y-only gives B/W image.
 U,V may have fewer bits than Y.
 Assuming 8-bit (256 colors), transformation is:
Y = 0.299*R + 0.587*G + 0.114*B
U = -0.169*R - 0.331*G + 0.500*B + 128.0
V = 0.500*R - 0.419*G - 0.081*B + 128.0
Subtractive color
 Pigments absorb specific colors, so they
subtract colors from a painting or document.
 To mix pigments, we choose pigments that
absorb just one color:




K: brightness (black to white)
Cyan: Blue + Green = White - Red
Magenta: Blue + Red = White - Green
Yellow: Red + Green = White – Blue
 This gives the CMYK system.
High quality color
 Its not possible to get most pure colors with 3
phosphors/pigments
(all colors are in the
convex hull of the base
colors).
 High-quality systems
use more colors (e.g. 7)
spaced around the
color wheel to provide
better coverage.
Light waves (EM radiation)
 Light is a form of electromagnetic radiation.
 E (electric) and B (magnetic) fields are at right
angles to direction of propagation.
2D light wave model
 Its convenient (for drawing and analysis) to
look at light wave propagation in 2D.
 Wavefronts represent maxima of E or B at a
given time instant.
Superposition
 Light (and other EM radiation) obeys
superposition:
 The E/B field due to many sources is the sum of the
field due to each source.
 A point source generates a spherical wave
field.
 An extended source can be represented as a
sum of point sources.
Wavefronts and Rays
 From superposition, we can derive that waves
propagate normal the the wavefront surface,
and vice-versa.
 The ray description is most useful for
describing the geometry of images.
Reflection
 Most metals are excellent conductors.
 They reduce the E field to zero at the surface.
 This is equivalent to a field of point sources at
the surface with opposite polarity.
 These sources re-radiate
the signal at the reflection
angle.
Reflection – Ray representation
 Using the ray representation, incident and
reflected light rays make the same angle with
the surface normal.
 Incident, reflected ray
and normal are all in
the same plane.
 If I, R, N unit vectors:
IN = RN
I(N  R) = 0
Refraction – wave representation
 In most transparent materials (plastic, glass),
light propagates slower than in air.
 At the boundary, wavefronts bend:
Refraction – ray representation
 In terms of rays, light bends toward the normal
in the slower material.