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 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 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] = [ ] [X] [G] = [ ] [Y] [B] = [ ] [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 *G *B U = *R *G *B V = 0.500*R *G *B

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.