Colorimetry

Colorimetry is the science of dimensional designations of colors. It provides means of mathematical formulas, the visual result of a color or viewing of color comparison numerically dar.

Subdivision

• The lower colorimetry based on the Grassmann laws and judges the similarity of colors. It 's not about the primary color stimulus, but the color stimulus, inasmuch as the colorimetry is a Farbvalenzmetrik. The additive color mixture applies the lower colorimetry since three components are combined in accordance with the sensitivity of the cones, the same color is achieved ( required here).
• The higher color metrics based on the application of the lower colorimetry and turns the color differences to. The main objective is to optimally adjust the dimensions of the valences of the color sensations.

Application

Colorimetry evaluates color measurements, so that the visual perception " color" can be fixed as color valence with colorimetric values ​​.

• The basis for color reproduction in printing.
• Basis for formulation in the color matching body color and instrumental color matching.
• Experimental basis of the theory of color, interprets and verifies the measurement results, which are based on color models. Thus color spaces can be measured by means of color systems and created for color practice.

Color measurement

Here color is always color stimulus, the perceived by the eye of a color stimulus sensation. Measurement target is not the (physical, spectral ) color stimulus, but the ( acting ) color stimulus. Less common but more accurately is the name Farbvalenzmessung. The measurement is performed in principle according to the Lambert -Beer law, but which is fulfilled only with monochromatic measurement. Therefore, intervals of wavelengths formed and measured ( as narrow as possible ).

It is possible now only an instrumental recording of the color stimulus, the desired numerical representation of the color stimulus as a color system requires therefore a mathematical apparatus or suitable filtering material. In other words, the measurement is made in accordance with the instrumental spectral composition of the light received, the transformation (Figure) to the three absorption pin carried by calculation. Finding the exact mapping function, the design of the color space, is currently still existing problem of Farbvalenzmessung.

Demarcation

The three human cones inevitably provide three color stimuli to be evaluated. Color measurement has a " meaning -oriented " measurement of three valences be. The determination of other metrics, such as the whiteness of paper, the iodine color, degree of bleaching numbers or colorimetry, are not to be understood in a narrow sense as color measurement. Similarly, a color recognition is not related to colorimetry, as the result of a color detection results in a color name or color number - but not a chromaticity.

Measurement methods

For measuring the color ( valences ) there are various methods.

Evaluation

For the analysis of the spectral numerical values ​​from the meter has to be converted to the desired color coordinates. Enforced have by the International Commission on Illumination ( CIE) defined Normspektralfarbwerte. These base figures are at a distance of one nanometer tabulated available.

Gewichtsordinatenverfahren

Based on this calculation method is that the color stimulus from the sum of the spectral color stimuli ( λ ) is calculated, the perceived color space spanning from the eye. It is usually the standard color values ​​are to be preferred. These are tabulated by the CIE standard colorimetric system for the.

For the calculation of this can now resolve for each of the wavelength- indexed values ​​Aλ as Aw in place. For the spectral radiance of the light source so Aλ etc. and thus integrated here d.lambda dw.

For the practical calculation is the integral switch on the sum d.lambda → δλ. Depending on the required accuracy in the color measurement now measuring intervals of 10 nm usual, simple colorimeters still using 16 values ​​in the 20 -nm spacing. When using the tables in 5 -nm spacing can be selected 5 nm for higher standards in accordance with ISO and DIN standards.

The addition of the product then yields the color value of X, is obtained in accordance with the color value and then. However, it is still normalized, mostly on, so with.

However, at body color or supervisory colors outgoing from the light source Sλ radiation is changed by the spectral properties of the surface in question. For the color stimulus function φ ( λ ) that meets the eye, the color in the proper sense, ie it must " influenced " spectral radiance are used. This is either the spectral reflectance curve β ( λ ) in surface color or the spectral Transmissionskurveτ ( λ ) with supervision colors. The spectral color stimulus is φλ βλ for the spectral reflectance now φλ = Sλ · and for the spectral transmittance in accordance with φλ = Sλ · τλ

And finally we get the color values ​​by appropriate weighting of the ordinate of the spectrum

Further evaluation process

Colorimeters

Since the 1980s, colorimeters are mostly spectrophotometer which automatically register the spectral curve and then run on the chip used, the necessary integration of the obtained measurement values ​​. The output of the measured values ​​can then be naturally in different coordinate (corresponding to the desired color space ) or as a spectral curve. By storing the color differences between the original color and a series of patterns can then spend. By converting to different (preferably normalized ) light sources can also be the metamerism of template to calculate sample.