Optics: measuring and testing – By shade or color
Patent
1990-11-06
1992-10-20
Evans, F. L.
Optics: measuring and testing
By shade or color
356425, G01J 346
Patent
active
051574640
DESCRIPTION:
BRIEF SUMMARY
The object of the invention is a viewing system which can be used for comparing reproduced and proof images, or for studying a non-reflecting image alone. Generally, it is advisable to use a colour definition method based on colorimetry in all applications of the technique in which the colours should be described unambiguously and precisely. The colorimetric method has been used and is still used in certain (not so many) colour reproduction equipment applications. Generally taken, this subject has been studied relatively little. As for commercial applications, the principles have not made a breakthrough into the printing trade. One reason for this is the lack of accurate and usable information on the factors affecting the perception of colours and the reproduction of colours in the reproduction process.
Numerous factors connected with the surroundings of the image and the image itself affect the colour effect given by the image, so there is no accurate quantitative method for describing how the colour effect appears. Many reproduction and proofing methods based on colorimetric colour analysis, some of which have been refined over the years, do not give satisfactory results, since the visual colour effect and its repeatability cannot be controlled. Even if these methods would give satisfactory results in practical use, the quantification of the colour effect and controlling its repeatability usually present a major problem.
Using the now-invented viewing system it has been possible to solve the above-mentioned problem in a limited scope with digital definition of the colour effect. This is based on the fact that when using the viewing system, different types of images will give a similar visual effect, provided the chromaticity defined with the colorimetric method, and the absolute luminance are the same for each colour in the images to be compared.
The now-invented system consists of a box, a viewing plane on the rear wall of the box, an opening in the viewing plane for the reflecting and non-reflecting image, equipment for illuminating the viewing plane and the reflecting image, and in the front wall of the box, a viewing opening. The box is ideally lined with a material reflecting as little light as possible. The light should ideally simulate daylight. The illumination system is such that no light is projected onto the non-reflecting image. This can be achieved e.g. by placing the non-reflecting picture behind the viewing plane. Ideally, the viewing plane and the images to be viewed are parallel to each other. The viewing opening is ideally placed symmetrically with reference to the images. The size and shape of the image openings depend on the size and shape of the images to be viewed. Moreover, the edges of the openings are preferably lined with material reflecting as little light as possible.
The viewing plane is usually medium grey, but it can be lined for example with the printing paper to be used.
When the non-reflecting image is behind the viewing plane, the edges of the opening in the viewing plane, and the duct between the opening and the image surface, are coated with a material (e.g. black) reflecting as little light as possible. The person viewing the image will see the lining of the interior walls, as the image is confined to the viewing plane surface.
The reflecting image can essentially be placed on viewing plane (whereby the distance between the image and the plane can, for example, be equal to the thickness of the paper with which the plane is lined).
Both the reflecting image and the non-reflecting image can be placed behind the plane, preferably at the same distance.
Both the viewing plane and the reflecting image can be illuminated with same lighting fixtures. There can, for example, be two lighting fixtures placed on opposite sides of the viewing plane, or for example four or more lighting fixtures placed of various sides of the viewing plane.
There can also be separate lighting fixtures for the viewing plane and the reflecting image. In this case, the viewing plane is a semi-translu
REFERENCES:
patent: 2873310 (1959-02-01), Valensi
patent: 3632217 (1972-01-01), Bartleson
patent: 4029418 (1977-06-01), Cottingham et al.
patent: 5033857 (1991-07-01), Kubota et al.
Lang et al., SMPTE Journal, vol. 87, Sep. 1978, pp. 579-582.
Evans F. L.
Teknillisen Korkeakoulun Graafisen Tekniikan Laboratorio
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