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 real-time 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 thered 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 typesallow the eye torespond to three-way 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 hullof the source.

(Line shows blackbody 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 moreintuitive 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 theconvex hull of the basecolors).

High-quality systemsuse 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 rayand normal are all inthe same plane.

If I, R, N unit vectors:

IN = RN

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.