Photography – Exposure control circuit – Color temperature compensation or detection
Reexamination Certificate
2001-07-05
2002-11-26
Perkey, W. B. (Department: 2851)
Photography
Exposure control circuit
Color temperature compensation or detection
C396S234000
Reexamination Certificate
active
06487372
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photometry device applicable to an SLR (Single Lens Reflex) camera, and more particularly to a photometry device with which exposure errors due to a difference of reflectivity of objects having different colors can be compensated.
Recently, reflection type photometry devices have been employed in most of cameras. The reflection type photometry device receives the light, which is reflected by an object and passed through an observing optical system of a camera, using a light receiving element, determines the brightness of the object based on the output of the measured value, and then calculates the exposure value of the camera based on the measured brightness. However, this type of the photometry device cannot detect the color of the object because of its structure. Accordingly, in such a device, the reflectivity of an object is generally assumed to be 18% and the exposure parameter is determined on this assumption. Therefore, regarding a whitish object whose reflectivity is greater than 18%, the determined brightness is greater than the actual brightness. If the camera controls an exposure operation based on the determined exposure value, the object is under exposed. A dark object whose reflectivity is less than 18% is measured to have a lower brightness. Therefore, such an object is over exposed. The difference of the reflectivity of the object may also occur depending on the color of the object. For example, when the color of an object is yellow, the reflectivity may be up to 70%. In such a case, if the standard reflectivity is assumed to be 18%, the exposure value is approximately 2 Ev lower than necessary. If the object color is blue, the reflectivity is approximately 9%. In this case, the object is over exposed by approximately 1 Ev greater than necessary.
Therefore, in the conventional photometry device, the photographer is required to guess the reflectivity of the object. Then, based on the reflectivity determined by the photographer, the exposure is controlled such that, if the object is a whitish or yellowish one having a relatively high reflectivity, it is to be overexposed, and if the object is a blackish or bluish one having a relatively low reflectivity, it is to be underexposed. With this operation, the above-described defects may be solved. However, accurately guessing the reflectivity of the object and controlling the exposure can only be done by experienced and skilled photographers. It is impossible to require all the photographers to do such an operation. Further, it is not preferable that a manual operation of the photographer is required for exposure. Further, if such a manual operation is required, cameras become unsuitable for automatic photographing which is the recent trend.
It may be possible to measure the color of the object, and perform exposure compensation based on the reflectivity corresponding to the measured color. If such a control is performed, an appropriate exposure value seems to be obtained automatically regardless of the color of the object. To perform such operation, a plurality of sensors for colorimetry may be provided inside the camera for selectively measuring different portions of the object. That is, light passed through a photographing lens of the camera is received by the plurality of sensors.
When such a structure is adopted, however, the spectral reflection characteristics of the object and the spectral radiant characteristic of an external light source are overlapped when the colorimetry is performed. Therefore, due to the spectral radiant characteristics of the external light source illuminating the object, it becomes difficult to measure the object color accurately. Then, the compensation amount of the exposure value includes errors, and the appropriate exposure may not be achieved.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved photometry device with which appropriate exposure values can be obtained regardless of a difference of reflectivity of the objects without being affected by the spectral radiant characteristics of a light source illuminating the object.
For the above object, according to an aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light sensor that performs a photometry operation with respect to an object, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a plurality of colorimetric sensors having spectral sensitivity characteristics different from each other, the plurality of colorimetric sensors performing a colorimetric operation with respect to an image of the object through a lens of the camera, an external light sensor that measures external light illuminating the object at spectral sensitivity characteristics corresponding to each of the plurality of colorimetric sensors, a light source color compensation amount calculation system that calculates a light source color compensation amount based on light source data, a colorimetric compensation amount calculation system that determines a color of the object based on the metered values output by the colorimetric sensors and compensated using the light source color compensation amount, and that calculates a colorimetric compensation amount based on the judged color, and a colorimetric compensation system that compensates for the exposure amount based on the colorimetric compensation amount. In such a photometry device, a predetermined fixed value is used as the light source data, and, if a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than a predetermined reference value, the colorimetric compensation amount is forcibly set to zero.
Alternatively, if a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than the predetermined reference value, operations of the colorimetric compensation amount calculation system and the colorimetric compensation system are not performed.
Further alternatively, the colorimetric compensation amount is compensated based on a coefficient obtained from a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor.
In each case, the photometry device may further be provided with a storage device, and light source data corresponding to an output of the external light sensor may be stored in the storage device. In this case, the fixed value can be calculated from the light source data stored in the storage device.
According to another aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light sensor that performs a photometry operation with respect to an object, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a plurality of colorimetric sensors having spectral sensitivity characteristics different from each other, the plurality of colorimetric sensors performing a colorimetric operation with respect to an image of the object through a lens of the camera, an external light sensor that measures external light illuminating the object at spectral sensitivity characteristics corresponding to each of the plurality of colorimetric sensors, a light source color compensation amount calculation system that calculates a light source color compensation amount based on light source data;
a colorimetric compensation amount calculation system that determines a color of the object based on the metered values output by the colorimetric sensors and compensated using the light source color compensation amount, and calculates a colorimetric com
Hirai Isamu
Iida Yoshikazu
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Perkey W. B.
LandOfFree
Photometry device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photometry device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photometry device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2919147