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` nu| !il
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`f 19865
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`(1)
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`TCL 1023, Page 2
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`

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`rae
`ey
`
`
`
`HAZEL ROSSOTTI
`COLOUR
`
`—
`
`Princeton University Press
`Princeton, New Jersey
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`VIZIO Ex. 1023 Page 0003
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`

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`Published by Ponccton Liniversity Press,
`4! William Street, Princeton, New Jersey 08540:
`
`Copyright © 1983 by Hazel Rossotti
`All nghts reserved
`First Pelican original edition, 1983
`First Princeton Paperback printing, with corrections, 1985
`
`LOC 84-1145]
`ISBN 0-691 -08369-%
`ISBN 0-691 - 02386 -7 (pbk.)
`
`Reprinted by arrangementwith Penguin Books Ltd,
`Made and printed in Great Britain
`by Richard Clay (The Chaucer Fress) Lid,
`Bungay, Suffolk
`Seain VIP Times
`
`Clothbound editions ofPrinceton University Press books are printed
`on acid-free paper, and binding materials are chosen for strength and durabilily.
`Paperbacks, while satisfactory for personal collections, are not usually suitable
`for library rebinding.
`
`
`
`CONTENTS
`
`List of Text Figures
`Foreword
`Preface to the Princeton Edition
`Introduction
`
`Part One: Light and Dark
`
`hoe
`
`. Light Particles
`. White Light on Clear Glass
`
`Part Two: Lights and Colours
`
`Ata&&
`
`2o~)
`
`. Steady Colours
`, Shimmering Colours
`. Special Effects
`. Lights
`
`Part Three: The Natural World
`
`. Air and Water
`. Earth and Fire
`. Vegetable Colours
`. The Colours of Animals
`
`Part Four: Sensations of Colour
`
`11.
`12.
`13.
`14.
`13:
`
`Light and the Eye
`Anomalous Colour Vision
`Colour Vision in Animals
`The Eye and the Brain
`Sorting and Recording
`
`Part Five: Technology
`
`16.
`17.
`
`Colour Reproduction
`Added Colour
`
`11
`12
`13
`
`19
`26
`
`37
`
`48
`55
`
`65
`77
`84
`91
`
`109
`122
`126
`130
`143
`
`169
`185
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`

`

`
`
`Contents
`
`Part Six: Uses and Links
`
`18.
`19,
`20.
`ok.
`
`Imparting Information
`Communicating Feelings
`Colour, Music and Movement
`Words and Colours
`
`Index
`
`Acknowledgements
`
`203
`209
`220
`ee di
`
`231
`
`239
`
`LIST OF TEXT FIGURES
`
`OoOo~]ohUroetHhome
`
`. Light waves
`. Prismatic colours
`. A home-made prism
`. From a rose window
`. How light travels through glass
`. How light bounces off glass
`. The dark eyes of houses
`. A single atom of matter
`. Glass
`. A metal
`. Interference of light
`. Printer’s blue and blood red
`. Oil patches and soap bubbles
`. Diffraction by twoslits
`. Diffraction by a grating
`. Polarization oflight
`. Three combs
`. A highly ordered fluid
`. Light sources
`. Laser light
`. Colours from white light
`. White light and tiny particles
`. Distant blue
`. White light and droplets
`. Reflected colour in clouds
`. The Blue Grotto
`. Sunset
`. Colours from a dewdrop
`. A pomary rainbow
`. A double rainbow
`. The Brocken spectre
`. How a glory occurs
`. Shiny graphite
`
`21
`
`23
`24
`27
`28
`29
`31
`32
`33
`33
`41
`46
`49
`50
`51
`52
`53
`57
`
`61
`65
`66
`67
`68
`69
`69
`71
`72
`72
`74
`75
`79
`82
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`
`
`List of Text Figures
`
`» Leaf green
`. Carrot orange
`- Delphinium biue
`38. The colourful juice of pickled red cabbage
`. Butterfly wings
`. Insect iridescence
`. Blue birds
`. How animals change colour
`. The human eye
`. A light twist
`. Changesin the retina
`. Brightness by night
`- Brightness by day
`. Cones and colour: a possible mechanism
`. Blue-green ambiguity
`- A bee’s-eye view?
`. Colours which recede or advance
`. The corner of the eye
`; Connections for contrast
`. Stereo
`. Brain waves
`, Coloured tops
`. Sidney Harry's top
`. Colours in space
`. Ostwald’s coloursolid
`. Munsell’s tree
`. Comparison of saturation
`» Mixing lights
`, Labelling with filters
`: Tops for colour measurement
`- A good match?
`. Maxwell's triangle
`. ‘Negative’ colours
`. CIE tongue diagram
`. Purple and white
`. Dominant wavelength
`. Colours and complementaries
`. Brightness
`73.
`Some common colours
`74,
`Colour and temperature
`75.
`Theflight of colours
`76.
`Colourtelevision
`
`153
`155
`156
`157
`159
`161
`163
`
`165
`166
`173
`
`List of Text Figures
`
`77
`78
`79
`80
`81
`82
`83
`
`. Phosphordots
`. Colour negatives and prints
`. Code for resistors
`. Coloured signals
`. Evolution of colour words
`. Heraldic tinctures
`. Names for colours
`
`175
`178
`206
`208
`223
`225
`226
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`
`142
`
`Sensations of Colour
`
`15
`
`SORTING AND RECORDING
`
`him from the donkey at that particular moment than to the average colour
`which the donkey would have if viewed by a laymanin diffuse light.
`Itis not surprising that the ability to look analytically can be cultivated by
`willpower and training; nor that those without training often prefer a
`naturalistic picture which represents colours as they remember them to
`those in which theartist tries to reproduce the actual light coming from the
`object. In much the same way, an observer will often select, as the most
`‘natural’ colour photograph, one in which the colours are actually brighter
`than those in the origina! scene, Colours selected to match memories from
`dreams, however, are often paler than those of similar objects we observe
`when awake.
`Colour sensations may often be even more dramatically altered by, or
`even produced by, factors other than light. Some forms of hysteria and
`hallucinogenic drugs enhance appreciation of colour: hallucinogens often
`provide experience of brightly coloured patterns which bearlittle relation
`to the real world, and those about to suffer attacks of epilepsy or migraine
`may see coloured rays and geometrical shapes before an attack. The blind,
`particularly if they are old, may have similar sensations, akin to seeing
`‘golden rain’ and coloured patterns. In childhood, a pressure on a closed
`eye was enough to produce patterns as exotic as Catherine wheels or
`peacock tails. In adult life, a firmer touch, preferably on the upper part of
`the eye, is needed to produce an inferior but none the less impressive result.
`Electrical and mechanical stimulation ofthe optic nerve and the visual areas
`of the brain can make us see colours; socan some acuteillnesses, andevena
`strong magnetic field. And so, of course, can memofy and dreams. But
`although we can experience an immense varicty of colour sensations pro-
`duced in these different, non-visual, ways, we have as yet only a negligible
`understanding of any of the mechanisms involved.
`
`‘To what extent can we record a colour? Can we impose any order on our
`rich vanety of colour sensations? If we can, would our scheme be entirely
`personal, or could we use it to communicate information about a colour?
`Howcan webesttell someone the exact colour we should like the new door
`to be?
`As we shall see in Chapter 21, there are manydifficulties in trying to
`describe colours with words. A request to paint the door turquoise would be
`likely to produce a fairly bright door in the greenish-blue (or might it be
`bluish-green?} range, neithervery pastel nor very murky. Perhaps we could
`get nearer to the colour we have in mind by a request to paint the wall the
`same colour as the curtains. But, though the two may s¢em a good match in
`one light, they may clash horribly in another (see page 152). And as they
`will have different textures, they will have different highlights; so although
`the colours of the two may ‘go’ very satisfactorily, they will certainly not
`match all over, even if the light falling on them happensto be identical. It is
`safer to choose from samplesof the actual paint, on the manufacturer's own
`colour card. But maybe the exact colour required is not available. ‘Please
`mix me...’ How does one continue? ‘Something between these two’;
`“Something like this, only lighter’; ‘A more subtle shade ofthat’; ‘A bluer
`version of this one.’ It is difficult to know howto specify, or how to produce,
`the colour required. And it may even be difficult to envisage precisely any
`colours which are not on the colour card.
`Perhapsit would help if we could arrange colours in somerational oruer
`and label them appropriately. We could then refer to them in much the
`same way as we can pinpoint a place by a map reference. Many child-hours
`must be passed in just this way, rearranging crayons, pastels or embroidery
`threads.It is easy enough to makealine of the rainbow colours, and join the
`TCL 1023, Page 7
`ends, through purple, to give a circle. But problems soon arise. Do black,
`grey and white count as colours? If they are to be included, where should
`they go? What should be done with pale colours: primrose, duck-egg blue,
`salmon? And what about the browns? One can imagine a cross-roads at
`yellow, with primrose leading to white on one side, and ochre leading to
`khaki, brown and black on the other. Perhaps, however, black and white
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`brightness (or value). The so-called ‘natural’ or ‘achromatic’ colours, black,
`the firsi. It seems we cannot arrange our coloured objects onaflat surface,
`but need some three-dimensional scheme.
`grey and white, are of zero saturation, and differ from each other only in
`Maybe it would be better to seek a more‘scientific’ classification than
`brightness. A series obtained by adding one hue, say blue, to white differs
`any subjective arrangement of coloured materials? We might try to specify
`only in saturation, as does a series obtained by adding a blue pigmentto a
`the colour of a sample by irradiating it with the light of a large number of
`grey one. If the same pigment were added to a white one in the same
`very narrow bands of wavelength and measuring the percentage of each
`proportions, the dusky, pale blue would differ from the clear pale blue only
`which the sample reflects. These measurements can be made extremely
`in brightness.
`easily, given the appropriate equipment. But the light which enters the eye
`There are many three-dimensional arrangements of colours, the best
`dependson the lighting as well as on the sample, so we would also need to
`known being those devised by Munsell and by Ostwald. Both are based on
`know the composition of the illumination. Even this does not tell us the
`the colour circle formed by joining the two ends of the spectrum through
`colour of the sample unless we know how the eye reacts to light of different
`purple (see Figure 58}. So the hue changes around the circumference of the
`wavelengths. Two materials may match exactly under one type of ililumina-
`circle, much as the hours progress around the face of a clock. Through the
`tion even if they sendlight oftotally different composition to the eye; we
`centre of the clock face. and perpendicularto it, like the axle of a wheel,
`know that many yellows can be matched by mixtures of red and greenlight.
`runsthe line representing the neutral colours, usually with white at the top,
`We might, however, combine, for each narraw band of wavelength,
`changing, through deepening greys, to black at the bottom. Radially, like
`measurements of the reflecting powers of the sample, and the composition
`spokes on a wheel, the saturation increases towardsthe rim,to give a space
`of the light source with our knowledge of the response of the retina.
`which can be filled in by different colours, according to which system is
`Although this procedure still needs laboratory equipment, it relates the
`being used.
`scientific measurements of the light reaching us to our perceptions of
`colour, assuming that the observer has normal colour vision, adapted for
`daylight viewing and uninfluenced by the effects (such as after-images,
`contrast of near-by colours, memory, expectation) which we discussed in
`the previous chapter. So we are attempting to chart,not just the stimulus of
`thelight entering the eye, but a normal observer's response to it. The idea of
`attempting to measure colour in this way soundsattractive, if somewhat
`complex. But do its advantages always outweigh those of map references
`with an ordered arrangement, albeit subjectively chosen and represented in
`three dimensions? Since both systems are usedin practice, we shall look at
`each in more detail.
`If we are to arrange a numberofcolours in any systematic order, we must
`decide what qualities we shall use to sort them. Letusfirst recall the waysin
`which light can vary. The sensation of colour depends primarily on the
`composition of the light, and partly on the intensity; and the composition
`may be usually described as a mixture, in a certain proportion, of whitelight
`with a ‘coloured’ light of a particular dominant wavelength within the
`visible spectrum. (For purple light, the ‘coloured’ componentis itself a
`mixture.) We can describe the primary sensation of colour in termsof hue,
`which refers to the greenness, blueness and so forth, and varies with any
`change in the dominant wavelength. The extent to which this wavelengthin
`fact dominates the light is known as saturation (or chroma). As the domin-
`ant wavelength is diluted with white light, the saturation decreases. An
`increase in intensity in ight of a particular composition increases the
`
`144
`
`Sensations of Colour
`
`Sorting and Recording
`
`145
`
`Pale colour
`Murky colour
`
`Vivid colour
`
`Black
`
`Figure 58. Colours in space The skeleton ofa colour solid. The ‘achromatic’ colours
`form the vertical backbonefram which the different hues radiate; red in one direction,
`green in the opposite one, and the others in between. For any one hue, the colour
`becomes more vivid the farther it is fromthe centre.
`
`TCL 1023, Page 8
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`Ostwald arranged his colours in a double cone, based on twenty-four
`different hues, arranged around the circumference (sce Figure 59). Each
`hue is combined, in a numberof fixed proportions, with each of eight
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`Hue (2)
`colourf°(compiementary to {1)}
`
`146
`{a}
`
`Sensations of Colaur
`
`Planes of constant dominant
`wavetength {hue}
`
`Full saturation atedge
`
`ib)
`
` Full
`
`Grey ans
`
`Figure 59, Ostwald’'s colour solid (a) Exterior view, (b} Vertical section.
`(Adapted, with permussion, from G. J. Chamberlin and D, G. Chambertin, Colour: lts
`Measurement, Computation and Appheation, Heyden, London, 1980.)
`equally spaced neutral colours from white to black. The resulting colours
`are arrangedso that brightness decreases vertically towards the bottom of
`the diagram, while saturation decreases towards the centre. Thus Ostwald’s
`colour solid consists of twenty-four triangles (one for each hue), arranged
`radially so that a vertical section through it gives two such triangles, for
`complementary hues, fused at the centre, Each position within the solid is
`
`Sorting and Recording
`
`147
`
`numbered ona grid system, so that any colour contained by thesolid can be
`specified by a map-reference.
`In Munseli's arrangement, saturation is increased by a serics of visually
`equal steps rather than by adding a fixed proportion of pigment; and there
`are nine neutral colours, rather than eight. As the numberof equalsteps of
`saturation at a particular hue and brightness depends on the hue, the arms
`are of different length in different parts of the solid. Munsell’s solid is
`therefore much fess regular than Ostwaid’s, and on accountof its untidy
`appearance is known as a colour‘tree’. A typical vertical section through it
`is shown in Figure 60. Each position in the tree, as in Ostwald’s cone, is
`encoded, thereby allowing colours to be specified. And the tree has one
`great advantage over Ostwald’s solid: whenever some new, dazzling pig-
`ment is made, it may be incorporated by extending an existing branch.
`
`Maximal
`
`
`
`saturation Hue (t}
`
`Black
`
`Hue (2)
`(complementaryto (1})
`
`Figure 60. Munsell's tree Vertical section (cf. Figures 39(b), page 146, and 83, page
`226).
`
`The two systems resemble each other in that the circumference is divided
`arbitrarily into hues, and the vertical axis is graduated into visually equal
`steps, which are obtained by asking large numbers of observers to estimate
`equal differences in brightness. But the two solids are based on diffcrent
`ways of varying saturation. While Ostwald used the ratio of neutral pigment
`to saturated pigment, Munsell again invoked visual assessment by the
`average observer.
`When Ostwald devised his colour solid, he was an old man whose sensi-
`tivity to blue was doubtless declining, which accounts for the slight com-
`pression in the blue region of the circumference. Swedish workers have
`attempted to correct this defect in Ostwald’s system by placing each of
`the four psychological primaries at right angles to one another on the
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`149
`
`Sorting and Recording
`
`Sensations of Colour
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`
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`Horzontalacan
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`circumference and dividing the segments between them into visually equal
`steps, constituting a more ‘natural’ colour circle for use as the basis of a
`three-dimensional colour solid.
`Although a colour solid is a useful concept, and may even be constructed
`asa display object of great visual and intellectual appeal, either swatches or
`books are more convenient for everyday use. Colour atlases, such as the
`Munseil Book of Colour, often represent vertical sections of a colour solid,
`cut through cach hue represented. For more specialist use, a restricted
`Tange of colours, varying by smaller gradations, may be reproduced as in
`collections for those who wishto specify the precise colourof arose petal or
`a sample of human skin or tooth.
`Such visual matching of colour is a stepwise process, a placing of the
`sample of unknown specifications between two standard colours whose
`specifications are known. But how can wetry to measure the colourspecifi-
`cations of a material if we have no standard colour which matches it? What
`can we do to try to measure ‘colour’, to produce specifications of hue,
`saturation and brightness?
`Since colour is a sensation, there is a lot to be said for the measurements
`being made by the eye. The humaneyeis, in fact, an excellent detector of
`differences of hue, and many people can assess the percentageof red, blue
`and yellow in a pigment with surprising precision. But human estimates of
`saturation, and of brightness, are much less reliable.
`The most precise visual methodsof attempting to specify colours,like the
`use of a colour atlas, involve matching. The simplest are those devised
`merely to measure saturation, as in the determination of the concentration
`of a single coloured componentin a liquid (see Figure 61).
`If the two solutions appear to be the same colour, the ratio of their
`concentrations is simply related to the ratio of the length of the two
`solutions through which the light has passed; and this mayeasily be found
`using a simple comparator involving either a plunger or a wedge.
`
`Figure 61. Comparison of saturation A fixed depth ofthe sample is viewed with one
`eye and a variable length ofstandard with the other. The geometry ofthe instrument is
`adjusted until the same depth of colour is observed by each eye.
`(a) Sampte.
`{b} Variation af depth of standard by means oftransparent plunger.
`
`fe) Variation ofdepth ofstandardby use ofwedge.
`
`(d) Split field, one halffrom each eyepicce.
`in the top two diagrams, the same depth used for sample and standard gives a darker
`field on the right. In the lower diagram, the length (1) ofstandard has been adjusted so
`that the two fields are indistinguishable In this exampie, d =2I, indicating that the
`Saiuration of the sample is half that of the standard.
`
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`
`150
`
`Sensations of Colour
`
`For many purposes, however, we need to know the hue, as well as the
`saturation. We again compare our sample with a colour which we can
`specify. But how can we vary this colour whilststill being able to specify it?
`One way is to mix coloured lights of known wavelength in known pro-
`portions. A simple arrangementis shown in Figure 62. The amountof red,
`blue and green light can be varied by horizontal and vertical movementof
`the filter assembly over the source of light, and the three lights are then
`mixed by diffusion and multiple reflections. More suphisticated devices,
`used mainly for
`research on colour,
`involve six lights of varying
`wavelengths. In each case the mixture of coloured lights, shone on to a
`white background, is matched with the unknown sample,illuminated from
`a standard source of white light.
`Alternatively, the sample may be matched by a patch of colouredlight
`which has been obtained by passing white light through three filters, one
`
`Bive fitter
`
`OOK x
`
`TiSNS35088reeatatet
`Bess
`
`
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`Green hitter
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`Red filter
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`Figure 62. Mixing lights The required mixture of red, blue and green itght may be
`oeenee byadjustingthat areaofcachfilter which lies over theaperture to the mixing
`
`Sorting and Recording
`151
`magenta, oneyellow and one blue-green (see Figure 63). Sets of suchfilters
`are available commercially for use in an instrument equipped with a stan-
`dardlight source and knownas the Lovibond ‘Tintometer. Thefull range of
`250filters of different depth for each of the three huesallows nearly nine
`million different colours to be obtained,
`including the full range of
`achromatic colours from white to black. The colourof the sampleis readily
`specified in terms of the three filters used to match it.
`MBG Y¥
`
`
`StandardENI iUy
`
`Sample
`Figure 63. Labelling withfilters The colour ofthe sample can be matched with that of
`light which has passed through three Lovibondfilters, magenta (M), blue-green (BG)
`and yellow (Y} ofspecified strength. A purplish bluesample, for example, would need
`a deep magenta (to absorb most ofthe green), a medium blue-green (to absorb some,
`bu: not all, ofthe red), and yellow ofappropriate depth to reduce the intensity ofthe
`colour to that of the sample.
`Instead of matching the light which reaches us from a sample with that
`from an unknown, we can exploit the phenomenon of persistence of vision
`and match only the sensations. Split discs, coloured in saturated blue, green
`and red, are placed on a revolving platform in such a way that the pro-
`portions of the three colours can be varied (see Figure 64). When the
`platform is spun at high speed, the sensations merge, just as if three
`coloured lights were superimposed, The areas of the three colours are
`adjusted until the colour of the spinning disc exactly matches that of the
`sample, which can then be expressedin terms of the proportionsof primary
`colours used.
`Nowadays, there is an increasing tendency to use photoelectric instru-
`ments for colour matching, instead of the eye of one or two individual
`observers. Such instruments monitor narrow bands over the whole visible
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`Sorting and Recording
`
`153
`
`152
`
`Sensations of Colour
`
`the sample, and then converting this information into the size of the
`stimulus which bombards eachof the three cone systems in a normal human
`eye. Finally, the responses to these three stimuli are combined to give the
`colour experienced by the ‘standard observer’. Inescapably, these instru-
`ments give results based on sensations experienced as a consequence of
`humanvision. But the vision js that, not of a few individuals, but of the
`‘standard observer’ built up from observations made by a large number of
`individuals selected for their normality ofvision. But even when the match-
`ing is done, rather approximately, by eye, it is seldom left for a single
`individual: more often two, or even three, observers are used.
`
`(a)
`
`(b) ae
`
`
`
`Figure 64. Tops for colour measurement (a) Split circular disc ofpaper ofstandard
`colour. (b} Stavhdardgreen, blue and red interlocked, exposing known areas ofeachfor
`colour mixing when the disc is rotated.
`
`Matching, whether by eye or machine, often gives different resu{ts with
`different sourcesoflight; and as matching implies identity only of response,
`this is no surprise. Two extreme examplesof identical colours produced by
`hght of very different composition were given in Table 3 (page 119).
`Imagine a pair of yellow pigments, onereflecting light of only 580nm and
`one reflecting only light of 540 nm and 630 nm,each at half the intensity of
`the first pigment. If both were illuminated with light containing equal
`intensities of the three wavelengths, the two pigments would match exactly,
`But if they were illuminated with light containing a slightly higher pro-
`portion of longer wavelengths, the second pigment would look redder than
`the first. Such ‘metameric’ pigments, which match only under one light
`source, are the bane of those who try to match clothes and accessories, or
`paint and fabrics (see Figure 65). Metamerism accounts for much of the
`
`whouses dyes such that any changein illumination causes almost the same
`change in colour for the different materials.
`Colour solids and atlases can give us no information about the compost-
`tion of the light which causesa particular colour, For charts relating colour
` 016
`
`Relative
`
`012}
`
`O04
`
`reflectance
`
`ates,
`
`i
`-
`i
`L
`i —
`400
`7
`500
`600
`700
`
`Figure 65. A good match? Thereflectance spectra oftwefabrics which match perfecily
`in daylight. (Reproduced, with permission, from W. D. Wright, The Measurement of
`Colour, 4th edition, Adam Hilger, London, 1969.)
`Green
`
`Wavelength (nim)
`
`
` Unsaturated greenlsh-yellow
`Blue-green
`
`Biue-violel
`Magenta
`Orange-red
`Figure 66. Maxwell's triangle Shows how many, burnorall, colours canbe represented
`as a mixture of three primary coloured lights. The nearer a point is to an apex 0.fthe
`triangle the higheris thepropartionoflight ofthe colour represented by that apex. The
`point X (50 per cent green, 35 per cent orange-red and 15 per cent blue-violet)
`
`TCL 1023, Page 12
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`LOWES 1023, Page 12
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`VIZIO Ex. 1023 Page 0012
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`i534
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`Sensations of Colour
`
`lo composition, we turn to the second, more‘scientific’ approach. Just as
`many coloursolids are based on a ring of spectral colours, joined through
`purpie, a triangle usually forms the basis of attempts to chart the colours
`produced by the mixing of lights. As early as 1855, Maxwell found thata
`great numberof colours could be produced by mixing lights of only the
`three ‘primary’ colours: orange-red, green and blue-violet. The colour
`resulting from a particular mixture can be represented by a point on a
`triangular grid (sce Figure 66). Many colourscan be specified in this way:
`but not all. Whichever three primary sources we choose, there are always
`some colours (including many pure spectral ones) which cannot be rep-
`resented by a point in, or on, the triangle; which confirms that we cannot
`always match one colour by a mixture of three others unless we allow
`ourselves the option of mixing one of the primary colours with the sample
`and then matching the result with a mixture of the two otherlights. Figure
`67 gives the recipe for obtaining a match for every visible wavelength with
`three primaries, Thus vivid yellow (570 nm) (cf. page 119} can never be
`exactly matched by red (700 nm) and green (546 nm); but if a little blue
`(436 nm) is added to the yetlow, a perfect match can be made. We can
`express this algebraically by stating that vivid yellaw can be matched by red,
`green and a small negative amountof blue. But since there is no scope for
`plotting negative contributions on a Maxwell triangle, colours such as vivid
`yellow cannot be represented onit.
`It is too bad that we cannot choose any three wavelengths which, when
`themselves mixed together, will produce alf visible colours. But there is
`nothing to stop us imagining that such ideal primary colours might exist;
`‘and if they did, they could be mixed in such a way as to produce three
`convenient heal primaries, such as Maxwell used. So we could draw a
`mathematical modification of Maxwell's triangle, with our three imaginary
`primaries at the corners. Points for the real ones, and for all other colours,
`would then be within it. Three such imaginary primaries have indeed been
`devised, such that any real colours can be represented as a mixture ofthe
`appropriate amounts of the three of them, and plotted as an idealized
`version of the Maxwell triangle. But not everyone is used to triangular
`graphs and the ruled paper may not be easy to obtain. Could we not usé
`squared paper instead? How many variables do we need? Since we have
`decreed that a real colour R can be matched by a mixture of our three
`Imaginary Primary Lights — say, | units of one, P units of the second and Lof
`the third -it might look as though we need the three variables,I, P, and L, to
`specify R. But we could also say that the brightness ofthe light is the sum S$
`of the three primaries (so S=1+P+L), mixed in the ratio of 1/S:P/S:L/S.
`And if we know I/S and P/S we already know L/S, because
`I/S+P/S+L/S=1. Since we are often more interested in colour than in
`
`425
`
`Sorting and Recording
`
`
`
`=
`Blue (436)
`
`+40
`
`+05
`
`0
`
`155
`
`These ‘positive’ Colours
`when mixed together
`
`MATCH
`
`mibdure.of pure Batch and
`these ‘negathvd colours
`
`Red (700) 415
`
`
`
`700
`400
`500
`600
`Wavelength of pure patch of fight (nm}
`Figure 67. ‘Negative’ colours Many pure spectral colours can be exactly matched with
`threeprimaries only by use of‘negative’ colours. When oneprimary is mixed with the
`‘pure’ patch oflight, this mixture can be matched by some mixture ofthe other two. For
`theprimary lights used here, the only colour which can be matched directly by the three
`primaries is a greenish yellow in the region of550.nm. (Reproduced, with permission,
`from F. W. Billmeyer and M. Saltzman, Principles of Color Technology, Interscience,
`New York, 1966, p. 33.)
`brightness, we could concentrate on the two quantities [/S and P/S which
`specify the colour. We could then use ordinary squared graph paper. lf we
`ever needed to know L/S,it would be easy enoughto calculateit. Andif we
`decided that, after all, we wanted to specify the brightness, we could
`representit on an axis rising vertically, oul of the paper. The final diagram
`would be much like a plan, with the two specifications of colour running
`north-south and east-west: of,if brightness is added, like a map which also
`shows heights, or isobars (or any third variable) superimposed onthe plan
`as a series of contours.
`a
`So all that we need in order to specify the colour of an object is a
`knowledge of the composttion of the light falling on it, of the modification
`
`TCL 1023, Page 13
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`LOWES 1023, Page 13
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`VIZIO Ex. 1023 Page 0013
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`156
`
`Sensations of Colour
`
`of the light by it, of the response of the normal humaneye, and of the
`quantities of three imaginary primary lights which would produce the same
`response; and a piece of ordinary graph paper. The Commission Inter-
`nationale de l' Eclairage (C1E), in 1931, defined the standard observer and
`three possible standard sources; and they produced tables showing the
`relationship between the observers’ response and the quantities of the
`imaginary primary tights which would in theory be needed to produce them.
`The tongue-shaped curve (see Figure 68) in the graph showsthe specifica-
`100% primary P
`‘ideal greary
`
`
`
`P
`
`157
`
`Sorting and Recording
`
`
`
`Figure 49. Purple and white The point £ for p =0-33, i =0-33 (and sal =k- 0-33) is
`‘equal energy’ white. Purples lie along the base line (see text}.
`
`100%primaryL
`raa
`Figure 68. CIE tongue diagram The tougue enclosesall visible colours, with thepure
`spectral ones lying along its curved edge. The inner triangle encloses those colours
`obtainable by mixing real primaries 436 nm, 546m, 700-nm (i.e. those enclosed in
`Maxwell's triangle of Figure 66, page 153).
`
`tions of the pure spectral colours as their values of i=1/S and p=P/S.
`(Modified definitions of the standard observer and the standard sources,
`eB introduced by the CIE in 1967, change only-details on the graph.) The
`100%primary| ane?
`diagram, known as a CIE chromaticity curve, has been used to depict
`colours, and the relationship between them, in a wide variety of situations.
`The enormous ceeress rf the ar diagrams percee ye
`aecan repressDud mixture of
`two lg us r pie
`vac :
`H3
`points which specily them. Sa purples, formed by mixing red and blue, he on
`the base-line of the ‘tongue’ (see Figure 69). A mixture of two parts red
`
`TCL 1023, Page 14
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`LOWES 1023, Page 14
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`VIZIO Ex. 1023 Page 0014
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`Sorting and Recording
`
`139
`
`o8
`
`C6
`
`Od ~
`
`158
`
`Sensations of Colour
`
`(770.nm) and onepart violet (380 nm) would lie at point X, twice as near to
`the red point as to the violet point. Since all the colours formed by mixing
`real lights tie inside the area enc