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Encyclopedia > Metamerism (color)

Metamerism is a psychophysical phenomenon commonly defined as the situation when two samples match in color under one condition, but fail to match under another condition. Psychophysics is the branch of psychology dealing with the relationship between physical stimuli and their perception. ...

The underlying basis of metamerism is that visual color matches are possible between two samples even though the spectral reflectance factors of the two samples are different. Thus many color matches are conditional. Conversely, if two samples have identical spectral reflectance factors they unconditionally match when viewed under the same conditions. (...assuming all else being equal, that is.) Spectral reflectance curves are generated by spectrophotometers. ...

Types of metamerism

Illuminant metamerism is the most typical kind of metamerism. It occurs when two samples match if viewed under one light source, but then do not match under a different light source.

Geometric metamerism occurs when two samples match when viewed from one angle, but then fail to match when viewed from a different angle. The reason for geometric metamerism is that the spectral reflectance factors of samples often vary when measured at different angles.

Observer metamerism occurs because of differences in color vision between observers. Often these differences have a biological source so that, for example, the ratio of long-wavelength-sensitive cones to medium-wavelength-sensitive cones may differ from one person to the next. Thus, two spectrally dissimilar surfaces may match for one observer when viewed under a certain light source but then fail to match when viewed by a second observer under the same light source. Color vision is the capacity of an organism or machine to distinguish objects based on the wavelength of the light they reflect or emit. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ...

Field-size metamerism occurs because the ratios of the three cone types in the retina vary not only between observers but also within a single observer depending upon the position on the retina. Light from a small object, for example, may illuminate only the central part of the retina where there are no short-wavelength-sensitive cones at all whereas light from a similarly illuminated object viewed from closer up will illuminate a greater area of the retina and will activate the short-wavelength-sensitive cones. It is quite possible, therefore, for two objects to match when viewed from one distance but then fail to match when viewed from a different distance. Human eye cross-sectional view. ...

Metamerism and color constancy

The phenomenon of metamerism is sometimes confused with color inconstancy. However, the former refers to a phenomenon with a pair of samples whereas the latter refers to a single sample. Color constancy refers to the observation that samples tend to retain their approximate daylight appearance when viewed under a wide range of different light sources. When samples fail to behave in this way we refer to this as color inconstancy. Color constancy is an example of subjective constancy and a feature of the human color-perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. ...

Relevance of metamerism and applications

In the printing industry, metamerism is often considered to be a source of great frustration. Artists paint with oil pastels, pastels, crayons, and various dyes and pigments, and each medium has unique spectral reflectance curves. The majority of color reproductions utilize combinations of cyan, magenta, yellow, and black inks or colorants. No combination of these inks can generate spectral matches to the colorants originally used to produce the original art. Therefore, a printed reproduction of an original artwork is only a metameric match to the original, and accurate viewing is thus dependent upon the spectral characteristics of the illumination used. A box of Pentel oil pastels Oil pastel is a painting and drawing medium with characteristics similar to pastels and wax crayons. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Crayola brand crayons A crayon is a stick of colored wax, charcoal, chalk, or other material used for writing and drawing. ... Yarn drying after being dyed in the early American tradition, at Conner Prairie living history museum. ... In biology, pigment is any material resulting in color in plant or animal cells which is the result of selective absorption. ... Cyan is a pure spectral color, but the same hue can also be generated by mixing equal amounts of green and blue light. ... Magenta is a color made up of red and blue light. ... Yellow is any color of light that stimulates both the red and green cone cells of the retina, but not the blue cone cells. ... Black is a color with several subtle differences in meaning. ... An ink is a liquid containing various pigments and/or dyes used for colouring a surface to render an image or text. ... A colourant is something added to something else to induce a change in colour. ...

Understanding what causes metamerism and knowing how you can spot and control[metamerism in paper]and graphic design applications is crucial to effective graphic design and commercial printing.

  Results from FactBites:
Color - Wikipedia, the free encyclopedia (3759 words)
The perception of color is influenced by biology (some people are born seeing colors differently or not at all; see color blindness), long-term history of the observer, and also by short-term effects such as the colors nearby.
Note that the color experience of a given light mixture may vary with absolute luminosity, because both rods and cones are active at once in the eye, with each having different color curves, and rods taking over gradually from cones as the brightness of the scene is reduced.
Structural color is a property of some surfaces that are scored with fine parallel lines, formed of many thin parallel layers, or otherwise composed of periodic microstructures on the scale of the color's wavelength, to make a diffraction grating.
  More results at FactBites »



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