Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1983-09-26
1986-02-11
Masinick, Michael A.
Facsimile and static presentation processing
Static presentation processing
Attribute control
358 41, 358 54, 358 55, 358 75, 358209, 358214, 358225, 358293, 358294, 250237R, H04N 909, H04N 316, H04N 336, H04N 911
Patent
active
045701792
DESCRIPTION:
BRIEF SUMMARY
This invention concerns the detection and measurement of light by photomultipliers or similar photoresponsive devices having a detecting surface whereupon the light to be detected and/or measured impinges. One example of an apparatus of this kind is a film scanner wherein a spot of light scans an area of film such as a photographic negative or positive and the transmitted light is arranged to fall on the detecting surface of a photomultiplier. Such detecting surfaces do not have exactly uniform response and it is known to arrange the light to fall on a predetermined static area of the surface. In this way, all specularly transmitted light is detected and measured.
In a colour scanner, the light transmitted by the film is split into a plurality of beams of different wavelengths, each beam impinging upon a predetermined area of a detecting surface of a respective photomultiplier.
Such an apparatus is described in U.S. Pat. No. 2,947,810. The transmitted light may be split into the separate beams by dichroic mirrors or by part silvered mirrors in either case with an appropriate colour filter in front of each detecting surface.
One problem which exists in measuring the transmission of light through a film is that dirt often exists on the surfaces of the film or scratches are present in the surfaces of the film. The dirt or the scratches scatter the light impinging on the film and the scattered light is no longer transmitted specularly in a controlled manner to the predetermined area of the detecting surface of the correct photomultiplier.
Such scattered light may be (a) lost (b) impinge upon the detecting surface outside the predetermined area and/or (c) impinge upon the wrong detecting surface within or outside the predetermined area thereof.
In each case, the response of the photomultipliers is incorrect and the electrical output signals of the photomultipliers do not faithfully represent the picture content of the scanned area of the film.
If the electrical output signals are used to produce a picture either directly as in a television system or indirectly by controlling the exposure of a photosensitive material, the incorrect signals resulting from dirt or a scratch on the surface of the film produce a line or spot of contrasting density which is particularly noticeable, for example, as a white spot or line on a colour print.
Similar incorrect output signals are obtained if, for example, faults or spots of dirt are on any optical surface of the apparatus adjacent the film.
An electronic partial solution to this problem is described in the above mentioned U.S. Pat. No. 2,947,810 and a further similar electronic partial solution is described in U.K. Specification No. 1409153.
The present invention seeks to overcome or minimise the problem of scratches in and/or dirt on film in an extremely simple manner and is based on the fact that, in a reproduction, changes in colour are much less noticeable than changes in density.
In accordance with the present invention, there is provided a film scanner with improved response to scattered light. The scanner converts light directed through a transparency into an electrical signal representative of the picture content of the transparency. The improved response is obtained by providing a photomultiplier or like photoresponsive device having a photosensitive detecting surface, a predetermined area of said surface being arranged to detect light specularly transmitted to the device, an attenuating filter covering said predetermined area whereby the response of the device to scattered light impinging upon that part of the detecting surface not covered by the filter is enhanced relative to the response of the device to the specularly-transmitted light impinging upon that part of the detecting surface covered by the filter.
In film scanning apparatus, the predetermined area is preferably coincident and commensurate with an image, on the detecting surface of the photomultiplier or like photoresponsive device, of the aperture of an objective used to focus the scanning spot onto a
REFERENCES:
patent: 2947810 (1960-08-01), Horsley
patent: 3304435 (1967-02-01), Norwood
patent: 4030817 (1977-06-01), Westell
patent: 4289275 (1981-11-01), Critchlow et al.
Eastman Kodak Company
Masinick Michael A.
Svihla Randall S.
Woods David M.
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