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Файл:Color Theory. Tutorial
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8. What groups of related colors are distinguished according to
color circle (wheel)
цветовой круг
color combination
сочетание цветов
color cone
цветовой конус
color harmony
цветовая гармония
contrasting colors
контрастирующие цвета
diameter
диаметр
equilateral triangle
равносторонний треугольник
Goethe's color wheel
цветовой круг Гёте
harmonious composition
гармоничное сочетание
inverted triangle
перевернутый треугольник
monotone
однотонный
obtuse angle
тупой угол
Ostwald's color wheel
цветовой круг Оствальда
related colors
родственные цвета
related-contrasting colors
родственно-контрастирующие
цвета
right-angled triangle
прямоугольный треугольник
shadow series
теневые ряды
triangle
треугольник
triangle vertices
вершины треугольника
zodiac sign
знак зодиака
the Shugaev's color wheel?
LECTURE VOCABULARY LIST
6. COLOR CHARACTERISTIC MEASUREMENTS
Quantitative characteristics of color
The color of any real radiation can be reproduced as a mixture of
white with monochromatic radiation. You need to choose the appropriate
wavelength of monochromatic radiation and the ratio of its emission power
to the white radiation power. This technique is used to analyze color
quantitatively. In this case the wavelength of the monochromatic radiation is
mixed with white to reproduce the color to be measured. The wavelength
of this radiation is called dominant wavelength. The ratio of the power of
the selected monochromatic radiation to the power of its sum with white
radiation determines the purity of the color.
Spectral colors are the purest ones because a high saturation cannot
be obtained for a given color tone, since these colors correspond to
individual monochromatic radiations without their mixture with white
radiation.
There are two methods for objective color measurement:
spectrophotometric method and photoelectric colorimetry.
International Commission on Illumination
The International Commission on Illumination (CIE) is the
international organization provided standards on principles and procedures
in the field of light and lightening. It was established in 1913. Today, it is
located in Vienna, Austria.
Color measurement system in X,Y,Z coordinates.
Chromaticity diagram
The International Illuminating Commission approved the
colorimetric method for quantitative measurement of color. This method
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uses three coordinates (X, Y, Z) which form a triangle. These coordinates
refer to three reproducible colors, chosen so that the real colors are located
inside the color triangle.
In practice, a two-dimensional coordinate system (X, Y coordinates)
is used instead of a three-dimensional system. It is determined by formulas
5 and 6:
Х = х/(х+у+z), (5)
Y = у/(х+у+z). (6)
CIE has developed the chromaticity diagram. Figure 9 present
the diagram in X and Y coordinates. Z coordinate can be calculated using
formula 7:
Z = z/(х+у+z). (7)
Since X+Y+Z=1, Z is usually omitted in calculations, and the color
according to the CIE system can be expressed by the X and Y values. The X
and Y chromaticity coordinates are determined by the position of any color
on the graph. All real colors are located inside the closed line. For all points
lying on these curves, the color purity is the same. The color purity of the
spectral curves is equal to 100 %.
Figure 9 shows the points on the curve limiting the area of all
possible boundaries of the chromaticity coordinates. These points refer to
spectral colors with the corresponding wavelength. They are indicated by
numbers on the line of spectral colors. Points A, C, E indicate sources of
illumination: A–tungsten filament; B and C–the same source with different
filters; A and C - illumination sources, the distribution of energy of which in
the visible region of the spectrum corresponds to the radiation energy
distribution of an absolutely black body at different temperatures (A–2854 K,
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C–6500 K); E is a source of illumination, the spectral density of which is
constant in the visible region of the spectrum.
Fig. 9. CIE chromaticity diagram: a is chromaticity diagram;
b is area of different colors
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Color can be characterized quantitatively by one color coordinate Y.
This is one of the main advantages of the system proposed by CIE.
In addition to the colorimetric system based on X, Y, Z coordinates,
other color measurement systems are used to determine such characteristics
as color tone, color purity, luminance or reflectance.
The color tone is characterized by the chromaticity diagram
(figure 9). Figure 9 presents the dominant wavelength λ, i.e. wavelength of
spectral monochromatic light, which determines the color tone of that light.
The dominant wavelength λ is found as follows: point E (figure 9) for
the illumination source E is connected by a straight line to the color point of
the given sample with chromaticity coordinates x and y, then this straight
line is continued to the line of spectral colors (figure 9a and b). The point of
intersection of this line with the line of spectral colors determines λ of this
sample.
The color purity of the sample on the graph is the ratio of
the photometric brightness of monochromatic radiation βλ to the total
brightness of radiation β. It is determined by the ratio of the distance from
point E to the point with the chromaticity coordinates of the given sample x
and y to the length of the segment drawn from point E through the point
with the specified x and y coordinates to the line of spectral colors. Colors
that have the same purity form closed curves on the chromaticity graph.
Figure 9b shows these solid lines.
The luminance or reflectance coefficient is measured directly by
a spectrophotometer.
The luminance coefficient is the ratio of the sample brightness to
the standard brightness from the uniform diffuser, measured under the same
lighting conditions at an angle of 45º.
The reflection coefficient is the ratio of the reflected light flux from
the sample to the reflected light flux from the uniform diffuser, measured
under the same lighting conditions.
Thus, the sample color can be determined through the dominant
wavelength, color purity, and reflectance (brightness). If the parameters
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have the same values, the samples are to have the same color. However, it
has been found that there is no direct relationship between a person's color
perception and the spectral composition of a sample color. When examining
a large number of samples of various colors, it was found that color
characteristics (dominant wavelength, color purity and brightness) do not
always provide the correct identification of the sample color, tone and
saturation.
If you arrange colored samples according to the row of ascending
dominant wavelengths, they do not reproduce the same colors of the samples
evaluated visually, especially for brown, beige, and yellow colors. Let us use
examples confirming this position. Two samples of different colors (yellow
and khaki) differ in color purity. However, they have the same dominant
wavelength. The other two samples have different dominant wavelengths,
but they are characterized visually as the same brown color. Apparently, this
is due to the fact that there is still no standard instrumental method for
assessing the sample color, although the above quantitative methods are used
in research projects.
Spectrophotometric method
The spectrophotometric method is used to determine the spectral
reflection coefficients. Then the color coordinates are calculated using the
formulas given above. The color coordinates and the spectral intensity of the
light source radiation in these formulas are fixed and determined from the
tables. The spectral energy distribution of the light source is also fixed.
According to GOST there are three standard light sources A, B and C with
a color temperature of 2843, 4800 and 6500 K, respectively.
The spectral reflectance of samples is measured using
spectrophotometers. Russian spectrophotometers: КЦ–3, ФО–1, ОС–16
and spectroradiometers have found a wide application.
The spectral reflection of a colored sample is determined according
to a white standard, which is usually the surface of freshly deposited
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magnesium oxide obtained by burning magnesium tape or shavings in air.
The reflection coefficient of magnesium oxide is conventionally assumed to
be 100% in the visible spectrum.
The spectrophotometric method is not widely used due to
the complexity of the equipment and the need to calculate color coordinates.
It is mainly used to provide measurements of high accuracy.
Colorimetric method. Colorimeter
The method of photoelectric colorimetry is based on the use of three
photoelectric radiation detectors, the spectral sensitivity curves of which
correspond to the curves of specific color coordinates, which, in turn, are
linearly related to the sensitivity curves of three human eye detectors.
The magnitude of the photocurrents of three such receivers is proportional
to the color coordinates of the measured sample. Since it is practically
impossible to manufacture a photodetector with the required sensitivity
curves, photodetectors are used for colorimetry in combination with light
filters that correct their sensitivity. There are also photoelectric
colorimeters with one photodetector, in front of which corrective light
filters are installed in series.
Let us consider the photoelectric concentration colorimeter КФК-2.
It is designed to measure the transmittance and optical density of liquid
solutions and solids, as well as to determine the concentration of substances
in solutions by constructing calibration graphs. It measures in certain parts
of the wavelength in the range from 315 to 980 nm emitted by light filters.
The instrument is successfully used to analyze the selectability of the dye
from the working solution for dyeing leather and fur. The colorimeter can
also be used to measure the transmission coefficients of scattering
suspensions, emulsions and colloidal solutions in transmitted light. It is used
in different technological processes for water supply, metallurgical,
chemical, food industries, agriculture, medicine and other areas of the
national economy.
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The normal operating conditions of the colorimeter are: ambient
temperature is 20±5 ºС; relative air humidity is 45–80 %; voltage is
220±22 V; frequency is 50 Hz.
The spectral range of the colorimeter is from 315 to 980 nm.
The range is divided into spectral intervals using light filters. Measurement
limits for transmission coefficients is from 100 % to 1 % (optical density is
from 0 to 2). The limit of the permissible absolute error of the colorimeter
for measuring transmission coefficients is ±1 %. The limit of the standard
deviation of an individual observation is 0.3 %.
LECTURE QUESTIONS
1. How can you determine the color purity?
2. What colors are the purest?
3. What is the name of the color measurement system using three
coordinates?
4. What color characteristic on the chromaticity graph is determined
by the dominant wavelength?
5. What is the brightness factor (coefficient)?
6. How can you determine the reflection coefficient?
7. What instrument is used to measure the spectral reflectance?
8. What is the operation principle of a calorimeter?
9. What parameters can be measured using the КФК-2 colorimeter?
10. What are the main practical applications of the КФК-2 colorimeter?
LECTURE VOCABULARY LIST
absolutely black body
абсолютно черное тело
ambient temperature
температура окружающей среды
chromaticity coordinates
координаты цветности
chromaticity diagram
график цветности
colorimeter
колориметр
dominant wavelength
длина волны преобладающего
излучения
frequency
частота
International Commission on
Illumination
Международная комиссия по
освещению
light filter
световой фильтр
photocurrent
фототок
photoelectric colorimetry
фотоэлектрическая колориметрия
photometric brightness
фотометрическая яркость
quantitative measurement
количественное измерение
reflectance coefficient
коэффициент отражения
relative air humidity
относительная влажность воздуха
spectral sensitivity curve
кривая спектральной
чувствительности
spectrophotometer
спектрофотометр
spectrophotometric method
спектрофотометрический метод
three-dimensional system
трехмерная система
transmission coefficient
коэффициент пропускания
two-dimensional coordinate
system
двухмерная система координат
7. CONTRAST: CONSTRUCTION PRINCIPLES
Contrast is one of the most important design elements. Color
harmony, coloration, light and shadow systems are often built on the principle
of contrast. It is often used to convey specific content of a work.
Contrast is described as a sharp difference between two adjacent colors.
There are two types of contrast: light (achromatic) and color (chromatic).
Let us use the example of a butterfly with symmetrical wings. One
wing is light on a dark background. Another one is dark on a light background.
Both wings are equal in size. In this case, one of the wings appears visually
larger. It seems to us that the whole butterfly is drawn crookedly.
The lightness contrast of a hue within the same color is called
achromatic (light contrast). The more different the brightness of the shades
is, the higher the contrast is.
Color contrast occurs between colors separated by two colors in the
spectrum. For example, between red (orange, yellow) and green, yellow
(green, blue) and blue, etc. Here, the degree of contrast depends on the
distance between the background color and the object color.
Simultaneous color contrast
Simultaneous color contrast occurs when two chromatic colors
(a chromatic color) interact with an achromatic color, resulting in a visible
change in color tone, accompanied by a simultaneous change in its lightness
and saturation (figure 10a, b, c).
The color tone may change due to the:
1) differences in lightness of compared color tones. Simultaneous
color contrast is most noticeable when the lightness of the compared colors
is approximately equal or when the background is darker than the object
located on it;
2) saturation of the compared color tones;
3) sizes of contacting tone areas.
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