Optics: measuring and testing – By shade or color – With sequential comparison of sample and standard
Patent
1984-02-03
1987-03-24
Evans, F. L.
Optics: measuring and testing
By shade or color
With sequential comparison of sample and standard
356414, 356419, 356418, 356425, G01J 351
Patent
active
046521364
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with a method for the measurement of the difference in the colour contents of two samples or of two component areas of a sample, in which method one or several sources of light as well as one light detector are used.
By means of techniques known in prior art, it is possible to measure the reflectivity, transmission or absorption of one sample at one wavelength, or their difference at two wavelengths, or the difference in reflectivity, transmission or absorption of two samples at one wavelength. In the case of two samples and two wavelengths, two separate measurements are required in order that the difference could be obtained.
The method in accordance with the invention is mainly characterized in that both samples, or component areas of a sample, are illuminated simultaneously and, from both samples or component areas of a sample, the light is passed simultaneously to the light detector, the lights to be measured from the samples or component areas of a sample being of different colours, as compared with each other, so that the light to be measured from the first sample or component area is absorbed weakly in the colouring agent and the light to be measured from the second sample or component area is absorbed strongly in the colouring agent, the colours of the lights to be measured from the samples or component areas of a sample are alternated with each other at an appropriate frequency, such as, e.g., at a frequency ranging from 1 c/s to 10,000 c/s, and the AC signal given by the light detector is used as the measure of the difference in the cololur contents of the samples or component areas of a sample.
By means of the method in accordance with the invention, by means of which the difference in colour between two samples is measured at two wavelengths, the difference in colour between the samples is obtained precisely by means of one measurement.
The samples for which the method in accordance with the invention is suitable may be solid, liquid or gaseous volume samples, or faces that reflect light, or films transparent to light.
The invention comes out in more detail from the following description and from the attached drawings, wherein
FIG. 1 illustrates the measurement process when local reddishness of the skin by the effect of increased circulation of blood is being examined,
FIG. 2 illustrates the measurement of component areas of a sample when the apparatus or the optics of the apparatus are rotatad,
FIG. 3 illustrates an embodiment of the method in which the alternation of the colours is produced by means of a mobile filter,
FIG. 4 illustrates an embodiment of the method in which the alternation of the colours is produced by means of a mobile mirror,
FIG. 5 illustrates an embodiment of the method in which the alternation of the colours is produced by means of light breakers, and
FIG. 6 illustrates the stabilization of the sources of light and automatic balance adjustment. In the description of the method, measurement of the difference in colour of two face samples is used as an example. The way in which the nature of the samples affects the details of the performance of the method is obvious for a person skilled in the art. Likewise, it is obvious that this method can also be applied in the ultraviolet and infrared ranges.
In the method in accordance with the invention, two lights of different colours are used, i.e. lights whose wavelength ranges are restricted in such a way that the average wavelengths of their wavelength ranges are different. The restricting of the wavelength range takes place in a way known to a person skilled in the art, such as, e.g., by means of a filter, grid, or prism. One of the face samples is called the face to be studied and the other one the reference face. Both of the faces are illuminated simultaneously, one with a light of one colour and the other with a light of the other colour, and the light reflected from both faces is allowed to act upon one light detector at the same time. The measurement geometry must be such that the angles
REFERENCES:
patent: 3237509 (1966-03-01), Fielding
patent: 3332313 (1967-07-01), Batson
patent: 3807873 (1974-04-01), Nakamori
Evans F. L.
Labsystems Oy
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