Reading 4 - The Morgan Kaufmann Series in Interactive...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: The Morgan Kaufmann Series in Interactive Technologies Series Editors: o Stuart Card, PARC o Jonathan Grudin, Microsoft o Jakob Nielsen, Nielsen Norman Group Evaluating Children’s Interactive Products: Principles and Practices for Interaction Designers Panos Markopoulus, Janet Read, Stuart MacFarlane and Johanna Hoysniemi HCI Beyond the GUI; Design for Haptic, Speech, Olfactory and Other Non-Traditional Interfaces Edited by Philip Kortum Measuring the User Experience; Collecting, Analyzing, and Presenting Usability Metrics Tom Tullis and Bill Albert Keeping Found Things Found: The Study and Practice of Personal Information Management William Jones GUI Bloopers 2.0: Common User Interface Design Don’ts and Dos Jeff Johnson Visual Thinking: For Design Colin Ware Moderating Usability Tests: Principles and Practice for Interacting Joseph Dumas and Beth Loring User-Centered Design Stories: Real-World U CD Case Studies Carol Righi and Janice James Sketching User Experience: Getting the Design Right and the Right Design Bill Buxton Text Entry Systems: Mobility, Accessibility, Universality Scott MacKenzie and Kumiko Tanaka-ishi Letting Go of the Words: Writing Web Content that Works Janice “Ginny” Redish Personas and User Archetypes: A Field Guide for Interaction Designers Jonathan Pruitt and Tamara Adlin Cost-lustifying Usability Edited by Randolph Bias and Deborah Mayhew User Interface Design and Evaluation Debbie Stone, Caroline Jarrett, Mark Woodroi'fe, Shailey Minocha Rapid Contextual Design Karen Holtzblatt, Jessamyn Burns Wendell, and Shelley Wood Voice Interaction Design: Crafting the New Conversational Speech Systems Randy Allen Harris Understanding Users: A Practical Guide to User Requirements: Methods, Tools, and Techniques Catherine Courage and Kathy Baxter The Web Application Design Handbook: Best Practices for Web—Based Software Susan Fowler and Victor Stanwick The Mobile Connection: The Cell Phone’s Impact on Society Richard Ling Information Visualization: Perception for Design, 2nd Edition Colin Ware Interaction Design for Complex Problem Solving: Developing Useful and Usable Software Barbara Mirel The Craft of Information Visualization: Readings and Reflections Written and edited by Ben Bederson and Ben Shneiderman HCI Models, Theories, and Frameworks: Towards a Multidisciplinary Science Edited by John M. Carroll Observing the User Experience: A Practitioner’s Guide to User Research Mike Kuniavsky Paper Prototyping: The Fast and Easy Way to Design and Refine User Interfaces Carolyn Snyder Morgan Kaufmann is an imprint of Elsevier Visual Thinking For Design Colin Ware AMSTERDAM - BOSTON ' HEIDELBERG I LONDON NEWYORK ' OXFORD ' PARIS ' SAN DIEGO 0 SAN FRANCISCO - SINGAPORE ' SYDNEY - TOKYO M MORGAN KAUFMANN PUBLISHERS 64 Graphical Code Shapes connected by contour. Thickness of connecting contour. Semantics Related entities, path between entities. Strength of relationship. Color and texture of Type of relationship. connecting contour. Shapes enclosed by a contour, or a common texture, or a common color. Contained entities. Related entities. Nested regions, Hierarchical concepts. partitioned regions. Attached shapes. = 1' Parts of a conceptual structure. world activate patterns of responding, such as sequences of eye movements. The processing of visual thinking also involves the interplay between pat— terns of activity in the non—visual verbal processing centers of the brain. Although pattern finding is something that everyone can do because it is a fundamental part of the process of seeing, designers must have an additional skill. They must see critically. This is very different from sim— ply seeing that a pattern is present and using that pattern for some cogni- tive task like finding a route using a map. The map designer must critically analyze which combinations of patterns will provide the best support for the set of cognitive tasks a map supports. This critical seeing may seem intuitive to the skilled designer, but this intuition is hard—won through years of experience honing critical perception. Because pattern perception is so central, we will return to this and many of the other issues raised in this chapter. Most large animals have worse color vision than humans. Color vision is of little benefit to grass eaters like zebras and cows—these animals have only two dimensions of color vision. The motion of a tiger’s prey is more critical than its color, and although cats, like grazing animals, have the physiological basis for two dimensions of color, it is extremely difficult to train them to respond to color. For the most part, they behave as if they Color Color vision makes it much easier to see the fruit ofthe West African Akee tree. 65 66 live in a grey—scale world. On the other hand, color is invaluable to fruit eaters; color lets them see the oranges in the tree or the red berries in the bush. Birds have even better color vision than humans, being able to distinguish four or more dimensions. Humans and the other great apes, omnivorous hunter—gatherers that we are, have three dimensions of color. The purpose of this chapter is to develop a theory—based approach to how color should be used in design. This will be somewhat incom- plete because color is a complex technical subject, although a surprisingly small amount of theory is needed to derive the most important aesthetic principles. The parts of color theory not covered include colorimetry and color reproduction. Colorimetry is the discipline dealing with the precise measurement and specification of color.‘ Color reproduction is the discipline dealing with how colors are printed on paper, as well as methods for transforming colors from some display medium, such as a computer monitor, to another, such as printed paper through color gamut mapping.- THE COLOR-PROCESSING MACHINERY There are two basic types of light receptors in the retina at the back of the eyeball: rods and cones. Rods, the most numerous type, are specialized for very low light levels. Rods are wasted on modern humans because they are overloaded at the light levels of our artificially lit world. These days most people rarely try to get around under starlight, and this is no longer an important survival skill. Unfortunately, we have no way of trading our rod receptors for cone receptors. Cone receptors are the basis for normal daytime vision, and they come in three subtypes—short-wavelength sensitive, middle-wavelength sensi— tive, and long-wavelength sensitive. These three different types of cones mean color vision is fundamentally three—dimensional. This is the reason that televisions and monitors have three types of liquid crystal filters, or three different—colored light—emitting phosphors in older cathode-ray tube monitors. David Williams, at the University of Rochester, has recently succeeded in obtaining images of the human retina and classifying the cones. Here are examples from two different people. What is immediately apparent in these images of retinas is that there are far fewer short—wavelength-sensitive cones (blue) than middle— or long—wave- length—sensitive cones. Compounding this, the few short—wavelength—sensitive cones are less sensitive to light than either the middle- or long-wavelength— sensitive cones. °The classic text dealing with color measurement as well as basic results is G. Wyszecki and W. S. Styles, T982. Color Science: Concepts and Methods, Ouantitative Data and Formulae (2nd ed.), John Wiley & Sons, Inc., New York. As of2007 it is still in press. Charles Poynton's site http://www. poynton.com/ColorFAQ.html is a very useful source of technical color information. 'See Maureen Stone, 2003. A Field Guide to Digital Color. A.K. Peters. The effects of mixing paints and printing inks are complex because ofthe ways light interacts with pigments—mixing colored lights is much simpler. Still, a reasonably complete range of colors can be produced with the colors cyan, magenta, and yellow. The reason these are different from the red, green, and blue of monitors is that these printing dyes subtract light reflected by underlying white paper, as opposed to emitting it. The Color-processing Machinery 67 1.0 0.8 0.6 0.4 0.2 Relative absorbance 400 500 600 700 Wavelength (nanometers) Sensitivity functions for the three classes of cone receptors. Cone receptors are sensitive to light having wavelengths between 400 and 700 nanometers (1 nm = 10‘9 meters). Note that the sensitivity distributions of long (L) and medium (M) wavelength-sensitive cones overlap considerably. The brain takes the difference between the two signals to get useful hue information. It is impossible to reproduce pure spectral colors with printing inks so the color bands below should only be taken as rough approximations to the actual hues. A consequence of our having few and weak blue-sensitive cones is that it is a mistake to show text or anything else with detail using blue on a dark background. The result is usually illegible. Showing small blue text on a black background is a bad idea. There is insufficient luminance contrast. A related problem occurs when using yellow for text. A pure yellow hue excites both the numerous middle— and long-wavelength cones, mak— ing yellow the lightest of all pure hues. Yellow can be almost as light as (ones in the fovea where there are no rods. Those sensitive to short, medium, and long wavelengths are colored blue, green, and red, respectively (Images from David R. Williams, University of Rochester.) 68 white, and small yellow text on a white background is extremely hard to read, but pure yellow is very distinct on a black background. Showing small yellow text on a white background is a bad idea. There is insufficient luminance contrast. Another interesting feature of the images of retinas on the previous page is the way the red- and green-colored cones are clumped together. We can see considerable detail in black and white images because for black-white detail it is only necessary for black and white parts of the image to fall on two or more different cone receptors, no matter which type. But the patchy nature of the different cone types means that we are far less able to see detail where the differences are purely chromatic. OPPONENT PROCESS THEORY A major transformation in the color signal from the receptors occurs in area V1, where information traveling along the optic nerve first arrives at the cortex. Neural networks add and subtract the cone signals in dif- ferent ways, transforming them into what are called the color-opponent channels.‘ There are three channels, designated red-green, yellow-blue, and black-white (or luminance), respectively. The red-green channel represents the diflerence between the signal from the middle- and long- wavelength-sensitive cones. This allows us to be highly sensitive to subtle red-green contrasts despite the overlap in the cone-sensitivity functions. The luminance chan- nel combines the outputs of long- and middle-wavelength-sensitive cones. The yellow-blue channel represents the diference between the luminance /\white yellow long wavelength sensitive cones medium wavelength sensitive cones short wavelength sensitive cones black ’Color-opponent theory can be traced back to Ewald Hering who published his ideas in Vienna in 1878. In V1, the raw signals from the cones in the retina are transformed. Some neurons compute differences between red- and green-sensitive cone signals. Some neurons compute the sum of red- and green-sensitive cones. Still others compute yellow-blue differences. The result is three kinds of color signals that are called color-opponent channels. channel and the blue cone signals. Note that although the black-white channel combines two type of cone information, it also differentiates in a spatial sense. Black-white differences are calculated simultaneously between all adjacent regions in the retina. CHANNEL PROPERTIES 0st of the important principles for effectively using color in desi can be erived from an understanding of the red-green, yellow—b e, and black hite color channels. What follows is a kind of annot ed list of channe roperties. Contrast. A phenomenon known as simultaneous cont st occurs in each of the hannels. The effect of simultaneous contras is distortion of the appearan r of a patch of color in a way that increses the difference between a color nd its surroundings. This is called 1i tness or brightness contrast when it o i urs in the black-white channel . d chromatic contrast when it occurs in eit er the red-green or yellow— - ue channel. Although contrast i often thought of as an ill ion, a kind of visual error, the mechanisms of ontrast help us see surface lors in the real world. Contrast comes aout because the visual system is etter at determining the diflerences - tween patches of light in the world n how much light is reflected fr them as measured by a light meter. Diffe ence information helps us dis ount the amount of light in our environmen enabling us to perceive w light or dark the surfaces of objects are whethe they are seen on a d winter day or a bright sunny day at the beach. It is ecause the brain 's sensitive to differences and not absolute values that we n repro- duc a reasonable facsimile of a beach scene at the movie theatre, espite t - fact that there may be one-hundredth the amount of light refl ting rom the screen compared to the real-world scene. Channel Properties 69 The two gray bars are exactly the same shade, but because ofsimultaneous lightness contrast the bar on the left seems darker than the one on the right. ...
View Full Document

{[ snackBarMessage ]}

Page1 / 4

Reading 4 - The Morgan Kaufmann Series in Interactive...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online