Design Realization lecture 24 John Canny 111803 Last

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. § RS 485 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 2 D. § 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.

2 D light wave model § Its convenient (for drawing and analysis) to look at light wave propagation in 2 D. § 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 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.