comparison of hue circles

 
This page presents the hue circle as defined in six historical and contemporary color description or color measurement systems:

• an 18th century color wheel – the ordering of hues published by Moses Harris in 1766, and respected through most later publications for artists.

• the MUNSELL hue circle – the first hue circle based on perceptual (visual) judgments of hue similarity, revised from 1910 to 1940

• the Swedish NCS hue circle – a conceptual hue ordering based on the Hering opponent functions, published in 1963

• the CIELAB hue circle – the UCS hue circle published by the CIE in 1976

• the CIECAM hue circle – the color appearance hue circle published by the CIE in 2003

• a mixing color wheel – a color wheel defined by the subtractive mixing of paints

The hue positions in these wheels were determined by means of the Munsell hue mensuration and the CIECAM/CIELAB locations of 24 criterion pigments or visual markers: optimal yellow .. (green yellow), hansa yellow PY97 (yellow), hansa yellow deep PY65 (orange yellow), isoindolinone yellow PY110 (yellow orange), cadmium orange PO20 (orange), perinone orange PO43 (red orange), naphthol scarlet PR188 (orange red), pyrrol red PR254 (red), quinacridone carmine PR N/A (deep red), quinacridone magenta PR202 (violet red), optimal magenta .. (red violet), dioxaine violet PV23 (violet), triphenylmethane violet PV39 (blue violet), ultramarine blue PB29 (violet blue), phthalocyanine blue PB15 (blue), optimal cyan .. (green blue), phthalocyanine green PG7 (blue green), permanent green deep .. (green), phthalocyanine yellow green .. (yellow green), raw sienna PBr7 (earth yellow), burnt sienna PBr7 (earth orange), venetian red PR101 (earth red) and burnt umber PBr7 (brown), based on the average position of paints listed in my guide to watercolor pigments. Hue positions in the Harris wheel are based on the specific pigments used in its printing. Hue positions for NCS were determined by visual comparisons to the NCS color atlas. Hue positions for the mixing color wheel are based on my watercolor mixing complements. Chroma (saturation) has been standardized to place all saturated hues on the circumference of each wheel.

 

an 18th century hue circle

The hue circle originates in a diagram of spectral hues published by Isaac Newton in Opticks (1704), his groundbreaking summary of late 17th century color research. Several subsequent publications intended for artists or naturalists explicitly copy his circular spectral scheme. But by the mid 18th century Newton's colors of light had been supplanted by colors of paint, organized around the three painters' primaries of red, yellow and blue.

The color wheel published in 1766 by the English entomologist Moses Harris was one of the most influential — it was studied and used by many 19th century English painters, including Joseph Turner — and it spawned many related color wheel systems: by English naturalist James Sowerby in 1809, colormaker George Field in 1817, and artist Charles Hayter in 1826. I've reproduced it here.

This is fundamentally a conceptual hue circle: the three "primitives" or primaries are spaced in equal 120° intervals around the circumference, their "mediates" orange, green and violet (purple in the original) are located at 60° intervals between them, with the remaining intervals divided again at 20° intervals. The six primitives and mediates provide the basic color names that are used to name the blends between them (for example, yellow, orange-yellow, yellow-orange and orange). A second hue circle, using orange, green and purple as primitives, was used to define the "compounds" olive, slate and brown. The primary wheel explicitly defines complementary hue pairs — red/green, orange/blue, yellow/violet — which combine to make "dirty, unmeaning" (achromatic) mixtures.

This basic conceptual framework was adhered to in artistic color wheels into the late 20th century. But the wheel itself has undergone radical transformation due to 19th and 20th century innovations in pigment chemistry, an important fact that is obscured by the historical consistency in the primary color names.

Harris cites the pigments vermilion (PR106), "king's yellow" (arsenic trisulfide or yellow orpiment, PY39) and ultramarine blue (PB29) for his primary pigments, although these are in fact orange red, yellow and violet blue pigments. The hue circle shown below adheres to these primary color pigment choices.

The first consideration is how the primary pigment choices may have affected the spacing of hues around the hue circle. Assuming that orange, green and violet were mixed to a visual standard (rather than a mixing formula, such as "orange is mixed from equal parts vermilion and orpiment"), then the choice of primaries forces expansion of the yellow to red and violet to violet blue hues, and a compression of the greens, reds and red violets.

More to the point, this spacing (assuming it is how the wheel mixtures were actually contrived) indicates that the 18th century would considered orange red (scarlet), rather than "pure" red, as the complement of green, and ultramarine (violet blue) as the complement of orange.

The second issue is that, as pigment chemistry changed, this hue spacing changed as well. Warm hues migrated toward yellow, compressing the "warm" color range, as primary red vermilion was replaced by lakes of carmine or madder, alizarin crimson, and most recently by quinacridone magenta (a violet red). The cool hues correspondingly migrated away from yellow as ultramarine was replaced by cobalt blue and most recently by phthalocyanine blues (blue or green blue).

In the traditional painters' color wheel:

Green is the complement of orange red
Blue green is the complement of orange red approaching red orange
Green blue is the complement of red orange
Blue is the complement of red orange approaching orange
Violet blue is the complement of orange
Violet is the complement of yellow

See the section on material trichromacy for more information.

 

an 18th century hue circle
in the original diagram, red is at the top and yellow at the lower right; subsequent wheels placed blue or yellow at the top, with red on the right or left

 

the MUNSELL hue circle

The Munsell Color System, introduced in 1915 and revised twice since then, is the oldest color model in common use today. The hue circle is divided into five equally spaced basic colors — yellow, red, purple, blue and green, in counterclockwise order — and five blends between them (yellow red, red purple, purple blue, blue green and green yellow). Each of these 10 color sections is divided into ten equal gradations, producing 100 hue intervals; the central or "pure" hue in each category is located at division 5 (yellow is at 5Y, red at 5R, etc.).

The hue spacing was determined through incremental perceptual comparisons between hues around the entire color circle, at different levels of chroma and lightness. Over small hue changes at a constant chroma, equal distances along the circumference represent equal perceived differences between hues. Thus, deep red and yellow orange are perceptually as different as green blue and blue green.

Hues positioned opposite each other on the hue circle represent visual complementary colors, which were determined by visual mixtures of colors on a color top, as described in the book review of Ogden Rood.

The Munsell hue and chroma spacing has been extensively researched and documented over the past century, and the Munsell is now commonly used as a benchmark spacing of hues when assessing the consistency or accuracy of newer color models, for example the CIELAB a*b* plane.

Most art instructors today still follow what is supposedly J.W.V. Goethe's definition of complementary colors as yellow/violet, orange/blue and red/green. The Munsell hue circle shows that these traditional complementary pairs are inaccurate. In Munsell:

Green is the complement of red violet
Blue green is the complement of violet red approaching red violet
Green blue is the complement of red
Blue is the complement of yellow
Violet blue is the complement of green yellow
Violet is the complement of yellow green

Note the large span between blue and green blue, and between violet and violet red. These hues comprise a large part of the Munsell color wheel, yet are infrequently used by most artists.

See the Munsell Color System for more information.

 

the MUNSELL hue circle

 

the Swedish Natural Color System (NCS)

NCS represents the culmination of the subjective or phenomenological tradition in color research. Color positions were determined as the average of many individual perceptual judgments, using imaginary or ideal color standards as a reference. Test individuals were asked to imagine the four unique hues — a "pure color" yellow, red, green or blue that contains no tint of any other hue — then to estimate the proportions of red+yellow, blue+red, green+blue or blue+yellow required to mix specific hue samples. Subjects could include black and/or white, also judged against imaginary standards, to describe pastel, darkened or grayed colors. Additional experiments demonstrated that this method was about as accurate as judgments based on physical samples of the unique hues.

The NCS is defined on phenomenological complementary colors — that is, they are not complementary colors by the normal definition. Hues opposite each other on the color circle typically do not mix to gray in subtractive or in additive color mixing. In addition, the unique hues themselves are not complementary.

The hue circle is divided into 100 units between neighbor unique hues, 400 in total. However hue spacing is not perceptually equal across each quadrant of the hue circle. The perceived color difference across 10 unit intervals in the red to blue hues is much larger than the perceived difference in the same interval across the green to yellow hues, and differences across the yellow to red hues are much larger than those across blue to green. These perceptual irregularities appear clearly when the NCS is represented in CIELAB, and are necessary in order to make the model geometrically consistent.

Note the expanded spacing of the deep yellow to magenta hues and the large span between light yellow and blue green, with the correspondingly excessive compression of the distance between magenta and middle blue. In NCS:

Green is the complement of deep red
Blue green is the complement of red orange
Green blue is the complement of orange red
Blue is the complement of orange yellow
Violet blue is the complement of greenish yellow
Violet is the complement of yellow green approaching green yellow

See the section on the Swedish Natural Color System for more information.

 

the Swedish Natural Color System (NCS)

 

the CIELAB a*b* plane

CIELAB is a color model proposed in 1976 by the CIE, an international body governing standards and methods in colorimetry. It requires electronic or photoelectric measurements of color and is widely used in the print and imaging industries and in manufacturing that requires high color control (such as automotives or paints).

Color locations are computed from the proportional stimulation to the R, G and B cones, mathematically transformed into a dimension of lightness (L*) and two perpendicular dimensions of hue, which do not match the Hering unique hues or the opponent process dimensions of the visual system (as measured in rhesus monkeys). The hue and chroma of all colors can be represented as a weight or position on these opponent dimensions, labeled a* (where red a+ is a positive value on a* and green a- is negative) and b* (yellow b+ vs. blue b-). Hue locations on the hue circumference can be expressed as a hue angle; the circle is not divided into equal intervals. The a* axis is conventionally shown with a+ (red) on the right; this has been reversed to facilitate comparison with other models.

CIELAB represents visual complementary colors, that is complements defined by mixtures of light or of surface colors visually blended by rotating them on a color top. All complementary colors have the relationship: hue (a*,b*) = hue complement (-a*,-b*). Hue, chroma and lightness are defined so that equal distances between any two colors in the CIELAB color space (over small distances) represent approximately equal perceived color differences in the color samples. However, when compared to MUNSELL, CIELAB appears to exaggerate color differences across green hues and to minimize color differences in blue greens and magentas.

CIELAB is not considered an especially accurate color model by color scientists, but it is quite useful to define color differences and color tolerances and thanks to extensive implementation via automated or electronic color management systems it is currently the de facto color measurement standard around the world.

Note the very small span between deep yellow and magenta (especially between orange and crimson), the large span between middle blue and turquoise, and the large span between blue green and light yellow. In CIELAB:

Green is the complement of red violet
Blue green is the complement of violet red approaching red violet
Green blue is the complement of deep red
Blue is the complement of yellow
Violet blue is the complement of green yellow approaching yellow green
Violet is the complement of yellow green

See the CIELAB uniform color space for more information.

 

the CIELAB a*b* plane

 

the CIECAM aCbC plane

CIECAM is the most recent color model proposed by the CIE, an international body governing standards and methods in colorimetry. It requires electronic or photoelectric measurements of color and is at the early stages of adoption in the print, imaging and manufacturing industries that requires high color control (such as automotives or paints).

The technical description of CIELAB (above) applies as well to CIECAM, with a few important exceptions. CIECAM is much better at modeling chromatic adaptation (the eye's of the perception of a "white" surface to match the color of the illuminant) and the contrast effects caused by display conditions — background color, illuminance level, the differences between projective or reflective media, and so on. CIECAM provides a more sensible spacing among green and blue hues, and probably the most accurate representation of visual complementary colors available today.

In CIECAM (as in CIELAB), all complementary colors have the relationship: hue (a*,b*) = hue complement (-a*,-b*). As in CIELAB, hue, chroma and lightness are defined so that equal distances between two similar colors represent approximately equal perceived differences in the color samples.

The diagram shows that these modern and technically defined visual complements are not the same as the 18th century complementary color pairs (yellow/purple, orange/blue and red/green) that are still taught in many art courses. The actual visual complement to orange is cyan blue, crimson goes with turquoise, magenta with blue green, and the complement of purple is yellow green. CIECAM is also probably a terminus in the development of "global" color appearance models. Current work is turning in the direction of context dependent color effects, in particular the effects of contrast and spatial size on color appearance.

As in CIELAB, note the very small span between deep yellow and magenta (especially between orange and crimson), the large span between middle blue and turquoise, and the large span between blue green and light yellow. In CIELAB:

Green is the complement of red violet
Blue green is the complement of violet red
Green blue is the complement of red
Blue is the complement of yellow orange
Violet blue is the complement of orange yellow
Violet is the complement of yellow green approaching green yellow.

See the CIECAM color appearance model for more information.

 

the CIECAM aCbC [chroma based] hue plane

 

a mixing color wheel

Mixing color wheels represent mixing complementary colors, that is, two paints that physically mix a pure gray or near neutral color are placed opposite each other on the circle. Mixing color wheels are standard issue to painters, although these hue circles are not based on color perception and cannot be accurately defined with paint mixtures.

The fact that the mixing hue circle arranges paints according to their colors is the source of mischief. Mixing complements are always imprecise because (1) all paints of a given hue ("color") are not effective mixing complements for all the paints of the complementary hue, (2) the mixing complements for a single paint may differ widely in hue (paints obliquely opposite each other on a mixing color wheel can also mix grays or neutral colors), and (3) chroma is as important as hue in defining mixing complement pairs (dull paints can serve as mixing complements to a much wider range of complementary colors). To appreciate the difficulties created by these problems, see the sections on substance uncertainty and mixing complementary paints.

The standard procedure for creating a mixing complement color wheel seems to be as follows: (1) place the three paints chosen as "primary" colors at the 0°, 120° and 240° locations on the hue circle; (2) determine their mixing complements, and place these "colors" at the opposite (180°, 300° and 60°) locations; (3) space the paint colors within each 60° section to make them as consistent as possible with the paints placed opposite them.

Once opposing paint pairs have been determined through mixing, this final spacing between neighbor colors is somewhat arbitrary. This ignores the actual saturation costs between paints that are not mixing complements, including the "primary" colors themselves. (That is, the fact that the mixtures of "primary" blue and magenta are duller than the mixtures of "primary" magenta and yellow would require that magenta and yellow be placed closer together on the hue circle.)

Within these limitations all the mixing complements shown below are based on my own careful measurements of watercolor mixing complements. I have located the color categories to correspond approximately to the choice of quinacridone rose (PV19) as a "primary" magenta, and phthalocyanine cyan (PB17) for a "primary" cyan. However, many artists still prefer alizarin crimson (a deep red) and phthalocyanine blue (a blue) as primary color choices, which would expand the spacing of reds, and the gap between violet and violet blue, even further.

Note that gaps or crowding in the hues are unavoidable, because the mixing complement paints for blue to green paints are concentrated in the smaller hue range from yellow orange (yellow ochre) to violet red (a quinacridone). This spreads out the warm hues and compresses the blues and greens.

Contrary to traditional color theory dogma, red is not the mixing complement of green, and purple (violet) is not the mixing complement of yellow. The mixing complement of green is violet red, and the mixing complement of middle red is blue green; the mixing complement of violet is yellow green, and light to medium yellows have no true mixing complements, but mix very dull greens with violet blues and tans with purple. In a mixing wheel:

Green is the complement of red violet
Blue green is the complement of red
Green blue is the complement of orange red
Blue is the complement of orange
Violet blue is the complement of yellow orange
Violet is the complement of yellow green

See the section on visual vs. mixing complements for more information.

 

a mixing complement color wheel

Last revised 03.14.2009 • © 2009 Bruce MacEvoy