Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
1999-12-20
2001-06-12
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06244710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ophthalmogical photographing apparatus having an image-capturing device for taking photographic images of an eye to be examined.
2. Description of the Related Art
There is known an ophthalmogical photographing apparatus which obtains an image of an examined eye as an electronic image by an image-capturing device, etc., instead of by conventional silver-halide film.
However, in the above-described conventional example, when an image of an examined eye is input as an electronic image, photographic tolerance (latitude) for a conventional silver-halide film is narrow. Therefore, for example, when an image of the eyegrounds is to be input, it is very difficult to obtain information efficiently from a papilla of the optic nerve (optic disk) having high luminance which contains much information and from the retina having low luminance, in particular, the macula lutea. Furthermore, the reflectance of the eyegrounds differs greatly from person to person, and when a photograph is taken using an inappropriate amount of light with respect to this reflectance, an inefficient image having a small area containing useful information with respect to a predetermined dynamic range is formed.
When a photograph of an image of an examined eye is taken, there are cases in which white flaring occurs at the peripheral portion of the image due to the degree of curvature of the cornea and photographic error. In this case, since information of the high-luminance portion, which is unnecessary for the predetermined dynamic range, is assigned closely, an inefficient image is formed. In a similar manner, a black aperture portion in the peripheral portion of the image is a factor which produces an inefficient image in which unnecessary information is assigned to a low-luminance portion.
Furthermore, in electronic images in general, when the amount of image data is large, a greater storage capacity is required, and processes, such as a replay, are thereafter slow. Some ophthalmogical photographing apparatuses use a technique for taking photographs continuously at very short intervals. However, in this case, a problem arises in that the processing speed per image must be shortened greatly.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an ophthalmogical photographing apparatus in which a decrease in image quality is minimized with respect to a primarily target area in the image of an eye being examined while reducing the image processing time.
To achieve the above-mentioned object, according to a first aspect of the present invention, there is provided an ophthalmogical photographing apparatus including: an image-capturing device, having a plurality of pixels, for converting an image of an examined eye into electrical signals; a digital conversion section for converting the output of the plurality of pixels into digital signals; first and second detection units for detecting a high-level signal and a low-level signal, respectively, of the level signals indicating luminance levels of the digital signals in predetermined area pixels of the image-capturing device; and a setting unit for setting a signal compression ratio of the digital signals of the digital conversion section on the basis of the high-level signal and the low-level signal.
The setting unit may set the compression ratio of level signals by the digital conversion section which is present between the high-level signal and the low-level signal to differ from the compression ratio of level signals by the digital conversion section which is not present between the high-level signal and the low-level signal.
Furthermore, the setting unit may set the compression ratio of level signals, by the digital conversion section which is present between the high-level signal and the low-level signal, to be smaller than the compression ratio of level signals by the digital conversion section which is not present between the high-level signal and the low-level signal.
A predetermined pixel area for detecting the high-level signal preferably contains the papilla of the examined eye, and a predetermined pixel area for detecting the low-level signal preferably contains the macula lutea of the examined eye.
A fixed-viewing target for guiding the fixed-viewing position of an examined eye is preferably provided, and the predetermined pixel area is changed in accordance with the fixed-viewing target.
According to a second aspect of the present invention, there is provided an ophthalmogical photographing apparatus including: an image-capturing unit for converting an examined eye image into electrical signals; a fixed-viewing target for directing the attention of the examined eye for fixed-viewing; an area setting unit for setting an image-capturing area of the image-capturing unit in accordance with the position of the fixed-viewing target; a luminance detection unit for detecting the luminance of the examined eye image information obtained from the image-capturing unit with respect to the area set by the area setting unit; and an image processing unit for performing signal processing on image information of the image-capturing unit in accordance with an output of the luminance detection unit.
According to a third aspect of the present invention, there is provided an ophthalmogical photographing apparatus including: an image-capturing unit for converting an examined eye image into electrical signals; an eye information generation unit for generating information for indicating whether an examined eye is the right eye or the left eye; a luminance detection unit for detecting luminance information with respect to a predetermined area of the image-capturing unit in accordance with an output of the eye information generation unit; and an image processing unit for performing signal processing on examined eye image information by the image-capturing unit in accordance with an output of the luminance detection unit.
In the accompanying drawings, illustrative embodiments of the invention are shown from which these and other objects, novel features, and advantages will be readily apparent.
REFERENCES:
patent: 5459536 (1995-10-01), Shalon et al.
patent: 5706071 (1998-01-01), Tokunaga
patent: 0 772 342 (1997-05-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Manuel George
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