Card – picture – or sign exhibiting – Photographic transparency viewer – e.g. – x-ray viewer
Patent
1992-06-30
1995-07-11
Dorner, Kenneth J.
Card, picture, or sign exhibiting
Photographic transparency viewer, e.g., x-ray viewer
40367, G02B 2702
Patent
active
054309646
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to a transparencies viewing device, more particularly, to apparatus for holding and illuminating X-ray and like transparencies.
BACKGROUND OF THE INVENTION
Medical X-ray transparencies usually are examined by placing them over the display area of a device commonly referred to as an illuminator. Conventional illuminators normally comprise a box-like structure enclosing fluorescent lighting tubes behind a semi-transparent light diffusing display plate defining the display area. Commonly, transparencies are retained on the surface of the display plate by pushing the upper edge of the transparencies under spring-loaded film-holder clips located along the top edge of the display plate.
Standard size illuminators have a display plate 17 inches high and 14 inches or multiples of 14 inches (i.e. 28 inches or 56 inches) wide. Usually, each 14 inch width of display plate has its own fluorescent tubes and control switch. Such display plates enable viewing full size X-ray films which measure 17 inches by 14 inches. In such cases, the sections of the display plate not covered by transparencies need not be illuminated. This eliminates unnecessary glare from areas outside the transparency.
When transparencies smaller than 14 inches by 17 inches are to be examined, they are typically retained on the display area in the same manner as full size transparencies, i.e., suspending them by means of the film-holders along the top of the viewer. This leaves a portion of the display area surrounding the transparencies fully illuminated and the resulting additional glare detracts from the visual perception of the person trying to study the transparency and assess the information it contains.
Often, transparencies contain several very transparent areas, and frequently, radiologists have to examine over-exposed transparencies. In these cases, considerable glare emanates through areas of the transparencies themselves.
An important factor in the interpretation of transparencies, is the ability to discriminate between various levels of light. This ability is determined by the Weber Law. E. H. Weber found that "the minimum perceptible difference in a stimulus is proportional to the level of the stimulus". Stated in terms of vision, as formulated by Fechner, .delta.L/L=K (Weber constant); Where .delta.L is the minimal detectable difference in luminance; and L is the luminance, see "Elemente der Psychophysic", G. T. Fechner, Leipzig, 1860, and "Visual Psychophysics", D. Jameson and L. M. Hurvich (ed.), Berlin, 1972.
Accordingly, if the eye is adapted to luminance L, .delta.L is determined. For a radiologist, maximal gray level discrimination is desired. Therefore, the observer's eye should be adapted to the luminance level of the image under study. In less benign conditions, a person reading an X-ray will be less able to perceive critical but minor shadings and nuances in the transparency. Moreover, protracted inspection of display areas under less benign conditions involves significant eye strain on the part of the observer.
While it is of course feasible for an observer to overlay masking strips on the display area and thus block unwanted and contrast-reducing light passing through the diffuser, as a practical matter, readers of X-rays rarely resort to such practice.
Attempts have been made in the past to provide viewing devices for X-ray transparencies which shield the eyes of the observer from light emanating from light sources other than the light passing through the transparencies, to obscure light in parts of the transparencies, and to reduce the contrast in transparencies when so required. However, these devices do not adapt the level of light to the transparency or to the sections being studied in the transparency.
In U.S. Pat. No. 1,988,654 to Haag, there is disclosed a light box which incorporates two manually movable curtains for masking all of the light transmitting surfaces of a diffuser up to the edges of a transparency.
U.S. Pat. No. 2,436,162 to Cadenas dis
REFERENCES:
patent: 1988654 (1935-01-01), Haag
patent: 2436162 (1948-02-01), Cadenas
patent: 3246412 (1966-04-01), Sommerhoff
patent: 3492486 (1970-01-01), Bischoff et al.
patent: 4004360 (1977-01-01), Hammond
patent: 4118654 (1978-10-01), Ohta et al.
patent: 4373280 (1983-02-01), Armfield, III
patent: 4510708 (1985-04-01), Pokrinchak
patent: 4637150 (1987-01-01), Geluk
patent: 4707080 (1987-11-01), Fergason
patent: 4799083 (1989-01-01), Knodt
patent: 4850675 (1989-07-01), Hatanaka
patent: 4855725 (1989-08-01), Fernandez
patent: 4908876 (1990-03-01), DeForest et al.
Jameson et al., "Visual Psychophysics" pp. 78-83.
English language abstract of JP 64-084141.
International Search Report in PCT/EP91/00065.
Inbar Dan
Teltsch Giora
Dorner Kenneth J.
Silbermann J.
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