Observer metamerism

When Munsell devised his color space, he did so on the basis of minimum observable color perception steps. But the problem with the Munsell System was one of reproducibility, which the CIE Standard Observer cured. In formulating a color match, one wants to be able to predict the correct concentration of colorants required, whose scattering and absorption properties are known, i.e.- the lightness, so as to match the sample submitted, starting with their spectrophotometric curves. In practice, this is not so simple, since two colors must have identical spectrophotometric curves to be exactly equal. It turns out that the human eye will identify the two colors to be equal if their spectrophotometric reflectances are reasonably close. Two colors may appear to be equal under Daylight illumination, but quite different under incandescent lamp illumination. These colors are known zus "metamers" and the phenomenon "metamerism". 

There is a second type of metamerism that is important to discuss and that is observer metamerism. This is where two objects appear to one observer to be a... 

Metameric pair n. A pair of colors, which match when viewed in a described way but which do not match if the viewing conditions are changed, thus, a metameric pair of samples exhibit the same tristimulus values for a described set of viewing conditions (observer, light source, geometry of the illumination, and viewing arrangement) but have different spectral distributions. Hence, they exhibit a match, which is conditional only. 

There are, necessarily, limitations to the above. Normally, the specular component of the reflected light is eliminated, and since the color matches are metameric, viewing conditions must be specified. Also, the greatest usefulness lies in the measurement of surface colors. The object should be opaque and nonfluorescent. The nature of the surface of tomato pur4e is far from ideal. Although many difficulties arise in borderline cases, and the result is dependent on the skill and color vision of the observer, the method has served a useful purpose. If however we examine the wording of the PMA specification, a sample shall contain as much or more red than that produced by spinning the specified Munsell discs. . . , it... 

This scenario is a common occurrence in plastics and other industries. The reason is very simple. Two objects having the same color, when viewed under one type of illuminant (daylight), appear to match. The same two objects when viewed under different types of illuminants (incandescent) do not match. This phenomenon is known as metamerism. Metamerism is a phenomenon of change in the quality of color match of any pair of colors, as illumination or observer or both are changed. 

Has many available observer/illuminant combinations that can be used for calculating tristimulus data and metamerism index. 

Works well for color formulation, measurement of metamerism, and variabie illuminant/observer conditions. Optimal for both quality inspection and research and development. 

Metamerism Metamerism is a phenomenon of change in the quality of color match of any pair of colors as illumination or observer or both are changed. 

When fields of different spectral distributions can be adjusted in relative radiance to eliminate all color difference, the result is termed a metameric color match. In a color-matching experiment, a test field is presented next to a comparison field and the observer causes the two fields to match exactly by manipulating the radiances of so-called primaries provided to the comparison field. Such primaries are said to be added this can be accomplished by superposition with a half-silvered mirror, by superimposed images projected onto a screen, by veiy rapid temporal alternation of fields at a rate above the fusion frequency for vision, or by the use of pixels too small and closely packed to be discriminated (as in color television). If the primaries are suitably chosen (no one of them shonldbe matched by ai possible mixture of the other two), a human observer with normal color vision can uniqnely match atty test color by adjusting the radiances of three monochromatic primaries. To accomplish this, it sometimes proves necessary to shift one of the primaries so that it is added to the color being matched it is useful to treat this as a negative radiance of that primary in the test field. The choice of exactly three primaries is by no means arbitrary If only one or two primaries are used, matches are generally impossible, whereas if four or more primaries are allowed, matches are not uniquely determined. 

In such cases—for example, matching a plastic dashboard with the fabric of an automobile seat—metameric matches must suffice these cannot be perfect for all viewing conditions and observers. Given the difficulty or impossibility of producing perfect matches, it is important to be able to specify tolerances within which imperfect matches will be acceptable. 

PVC. Such problems often respond to blends of suitable colorants for example, achieving a red coloration with a blend of red pigments. Metamerism may also occur with differences in angle of light incidence or reflection, and is subject to individual variability in the observer. 

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