Hue can typically be represented quantitatively by a single number, often corresponding to an angular position around a central or neutral point or axis on a color space coordinate diagram (such as a chromaticity diagram) or color wheel, or by its dominant wavelength or by that of its complementary color. The other color appearance parameters are colorfulness, saturation (also known as intensity or chroma),[2]lightness, and brightness. Usually, colors with the same hue are distinguished with adjectives referring to their lightness or colorfulness - for example: "light blue", "pastel blue", "vivid blue", and "cobalt blue". Exceptions include brown, which is a dark orange.[3]
The concept of a color system with a hue was explored as early as 1830 with Philipp Otto Runge's color sphere. The Munsell color system from the 1930s was a great step forward, as it was realized that perceptual uniformity means the color space can no longer be a sphere.
As a convention, the hue for red is set to 0° for most color spaces with a hue.
Munsell hues; value 6 / chroma 6
5R
|
5YR
|
5Y
|
5GY
|
5G
|
5BG
|
201 130 134
201 130 127
201 131 118
200 133 109
197 135 100
193 137 94
187 140 86
181 143 79
173 146 75
167 149 72
160 151 73
151 154 78
141 156 85
127 159 98
115 160 110
101 162 124
92 163 134
87 163 141
82 163 148
78 163 154
73 163 162
5BG
|
5B
|
5PB
|
5P
|
5RP
|
5R
|
73 163 162
70 162 170
70 161 177
73 160 184
82 158 189
93 156 193
104 154 195
117 151 197
128 149 198
141 145 198
152 142 196
160 140 193
168 138 189
177 135 182
183 134 176
188 132 169
193 131 160
196 130 153
198 130 146
200 130 140
201 130 134
Opponent color spaces
In opponent color spaces in which two of the axes are perceptually orthogonal to lightness, such as the CIE 1976 (L*, a*, b*) (CIELAB) and 1976 (L*, u*, v*) (CIELUV) color spaces, hue may be computed together with chroma by converting these coordinates from rectangular form to polar form. Hue is the angular component of the polar representation, while chroma is the radial component.
Preucil[8] describes a color hexagon, similar to a trilinear plot described by Evans, Hanson, and Brewer,[9] which may be used to compute hue from RGB. To place red at 0°, green at 120°, and blue at 240°,
Equivalently, one may solve
Preucil used a polar plot, which he termed a color circle.[8] Using R, G, and B, one may compute hue angle using the following scheme: determine which of the six possible orderings of R, G, and B prevail, then apply the formula given in the table below.
More information , ...
Ordering
Hue region
Orange
Chartreuse
Spring Green
Azure
Violet
Rose
Close
Note that in each case the formula contains the fraction , where H is the highest of R, G, and B; L is the lowest, and M is the mid one between the other two. This is referred to as the "Preucil hue error" and was used in the computation of mask strength in photomechanical color reproduction.[10]
Hue angles computed for the Preucil circle agree with the hue angle computed for the Preucil hexagon at integer multiples of 30° (red, yellow, green, cyan, blue, magenta, and the colors midway between contiguous pairs) and differ by approximately 1.2° at odd integer multiples of 15° (based on the circle formula), the maximal divergence between the two.
The process of converting an RGB color into an HSL color space or HSV color space is usually based on a 6-piece piecewise mapping, treating the HSV cone as a hexacone, or the HSL double cone as a double hexacone.[11] The formulae used are those in the table above.
Additional images for hue in the HSL and HSV systems
An image with the hues cyclically shifted in HSL space
The hues in this image of a painted bunting are cyclically rotated over time in HSL.
One might notice that the HSL/HSV hue "circle" do not appear to all be of the same brightness. This is a known issue of this RGB-based derivation of hue.[12]
Usage in art
Manufacturers of pigments use the word hue, for example, "cadmium yellow (hue)" to indicate that the original pigmentation ingredient, often toxic, has been replaced by safer (or cheaper) alternatives whilst retaining the hue of the original. Replacements are often used for chromium, cadmium and alizarin.
Hue vs. dominant wavelength
Dominant wavelength (or sometimes equivalent wavelength) is a physical analog to the perceptual attribute hue. On a chromaticity diagram, a line is drawn from a white point through the coordinates of the color in question, until it intersects the spectral locus. The wavelength at which the line intersects the spectrum locus is identified as the color's dominant wavelength if the point is on the same side of the white point as the spectral locus, and as the color's complementary wavelength if the point is on the opposite side.[13]
Hue difference notation
There are two main ways in which hue difference is quantified. The first is the simple difference between the two hue angles. The symbol for this expression of hue difference is in CIELAB and in CIELUV. The other is computed as the residual total color difference after Lightness and Chroma differences have been accounted for; its symbol is in CIELAB and in CIELUV.
Alternative approach is to use a systematic notation. It can be a standard angle notation for certain color model such as HSL/HSV mentioned above, CIELUV, or CIECAM02. Alphanumeric notations such as of Munsell color system, NCS, and Pantone Matching System are also used.
Frank Preucil, "Color Hue and Ink Transfer … Their Relation to Perfect Reproduction", TAGA Proceedings, p 102-110 (1953). [TAGA article #T530102, paid registration required from TAGA]
Brewer, Cynthia A. (1999). "Color Use Guidelines for Data Representation". Proceedings of the Section on Statistical Graphics. Alexandria, VA: American Statistical Association. pp.55–60.
This article uses material from the Wikipedia article Hue, and is written by contributors.
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