Optics: measuring and testing – By dispersed light spectroscopy – For spectrographic investigation
Patent
1997-06-03
1998-12-01
Font, Frank G.
Optics: measuring and testing
By dispersed light spectroscopy
For spectrographic investigation
356323, 356324, 356302, 356303, G01J 340
Patent
active
058446800
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an apparatus and a method for measuring and analysing spectral radiation. The term "spectral radiation" refers to radiation which spans a specific wavelength range. In particular, the invention relates to a device and a method for measuring and analysing the colour characteristics of passively or actively irradiating objects.
In the following, the problem to be solved by the invention and its solution will be described with reference to the example of an apparatus and a method for measuring and analysing of the spectral characteristics of colours, that is, of radiation which is in the visible wavelength range of between 380 and 780 nanometer (nm). The invention, however, is not restricted to the range of visible light but may also be used for radiation having a shorter or, as the case may be, longer wavelength.
The colour of surfaces is a fundamental characteristic of all objects which play a role in daily life, for example, clothing, items of furniture, and basic commodities such as automobiles, etc. The sensation created by colour occurs, for example, in the case of an illuminated surface where the incident light is absorbed or reflected in such a way that the light reflected from the surface displays a specific spectral course which is perceived by the observer as colour. In order to manufacture colours and coloured surfaces in a reproducable way it is necessary to determine said spectural characteristic.
Knowledge of the spectral characteristics of colour is also important in order to accurately reproduce colour by photographic means, i.e. in printed matter or on film, etc., and in particular, in order to detect colour by electronic means, to tranfer the recorded data, and to accurately reproduce colour on the television screen and the visual display unit.
The spectral distribution of the light which, for example, is reflected from a coloured object, and which creates a specific colour sensation is referred to as the colour stimulus function .phi.(.lambda.). On the one hand, the colour stimulus function is determined by the spectral distribution of the light S(.lambda.) which strikes the object, and on the other hand by the reflectance function .sigma.(.lambda.) which depends on the wavelength characterizes the reflectivity. The colour stimulus function is expressed as follows distribution of the light source, and the reflectance function.
If the light is not reflected from the object but passes through the object, the reflectance function is replaced with the transmission function .tau.(.lambda.).
As the colour stimulus function is a function of the spectral distribution of the light which strikes the surface, this means that the colour sensation may change, if the spectral power distribution changes. Such differences can be observed, for example, when an object is first illuminated with natural light metamerism and then with artificial light.
It has been shown that the colour sensation which a colour elicits from a so-called standard observer can be described in terms of three variables, so-called primary variables. According to this theory the colour values, X, Y, and Z, of one colour, which are elicited by the colour stimulus function .phi.(.lambda.) are determined by means of the following integrations: function, whereas x, y, and z are the standard spectral value function as a function of .lambda.. In 1931 a corresponding standard for colour values was established by the CIE (Commission Internationale de l'Eclairage) for the observation of small areas of colour, in particular, at a visual angle of of 2.degree.. As a supplement to this system, a 10.degree. system was introduced in 1964. In addition to these standards, there are also other colour standards which have been established by other standards organizations, which, as a rule, are based on the Young-Helmholtz three-colour theory.
There are a plurality of devices for measuring the colour characteristics of an object, the most important of which are briefly described in the following.
A typical
REFERENCES:
patent: 3715163 (1973-02-01), Mitchell
patent: 4111556 (1978-09-01), Grisar et al.
patent: 5210590 (1993-05-01), Landa et al.
BYK-Gardner GmbH
Font Frank G.
Ratliff Reginald A.
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