Photography – Exposure control circuit – Color temperature compensation or detection
Reexamination Certificate
2001-02-16
2003-03-18
Adams, Russell (Department: 2851)
Photography
Exposure control circuit
Color temperature compensation or detection
C396S233000
Reexamination Certificate
active
06535693
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, in most cameras, reflection type photometry devices are employed. 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 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. Regarding a dark object whose reflectivity is less than 18%, such an object is over exposed in order to increase an exposure value. 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, to accurately guess the reflectivity of the object and control the exposure can be done only by experienced and skilled photographers. It is impossible to have all the photographers 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, the camera becomes unsuitable, as the recent trend is for automatic photographing.
Recently, there is suggested a camera provided with a photometry device which divides the light from object into three-primary color components, and determines the color of the object based on the photometry outputs of respective color components. Since the color of the object is automatically determined, the above-described photographer's operation becomes unnecessary. However, depending on the color purity of the object, the determined compensation value may not precisely correspond to the actual color of the object. For example, given that the object color is blue, the blue purity could fall in various conditions. That is, the blue purity of the object may be relatively high, or the purity may be relatively low and the light from the object may include red and/or green components as well. Since the blue purity could have various levels even if the object color is determined to be blue, it is not reliable if the compensation value corresponding to pure blue is determined to be the compensation value for such an object. That is, if the compensation value corresponding to pure blue object is used for the object whose blue purity is relatively low, the compensation value may cause over-exposed condition. On the contrary, if the compensation value is determined based on an object having relatively low blue purity, the pure blue object may be under-exposed.
Furthermore, when the above-described compensation is applied, inappropriate compensation values may also be obtained depending on the contrast of the object. That is, a bright portion of the object having a higher contrast has more influence on the compensation value than a bright portion of an object having a lower contrast. For example, when a portion of the object has a relatively high reflectivity and another portion has a relatively low reflectivity, if the exposure compensation is applied based on the portion having the low reflectivity, the portion having the high reflectivity may be over-exposed. In such a case, it is difficult to determine an appropriate exposure for an entire object.
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 difference of reflectivity, color purity and contrast of focused objects.
According to an aspect of the invention, there is provided a photometry device for a camera, which includes a normal light sensor having spectral sensitivity characteristics close to visual sensitivity characteristics, a plurality of colorimetric sensors having spectral sensitivity characteristics that are different from each other, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a colorimetry system that judges a color of the object in accordance with the outputs of the plurality of colorimetric sensors, and a compensation amount determining system that determines an exposure compensation amount in accordance with the color judged by the colorimetry system. The compensation amount determining system compensates for the exposure compensation amount determined by the compensation amount determining system in accordance with differences among the outputs of the plurality of colorimetric sensors.
With this configuration, appropriate exposure values can be obtained regardless of the difference of the reflectivity and color purity of objects.
Optionally, the compensation amount determining system may compensate for the exposure compensation amount such that the exposure compensation amount is made greater when the differences are greater.
In a particular case, the normal light sensor may include a normal light photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from approximately 500 nm through 600 nm, and the plurality of colorimetric sensors may include a blue light photometry sensor for metering blue light component, a green light photometry sensor for metering green light component, and a red light photometry sensor for metering red light component.
Further optionally, the compensation amount determining system calculates a difference between an output of one of the plurality of colorimetric sensors, and an average of outputs of the other of the plurality of colorimetric sensors, and the compensation amount determining system compensates the exposure compensation amount in accordance with the difference.
In the above case, the compensation amount determining system may compensate for the exposure compensation amount such that the larger the difference is, the greater the exposure compensation amount is.
Still optionally, each of the plurality of colorimetric sensors may have a light metering surface divided into a plurality of photometry areas, and the compensation amount determining system may determine the exposure compensation amount in accordance with the outputs at least one of the plurality of photometry areas.
In the above case, at least one of the plurality of photometry areas may include a center of an object subjected to be metered.
Alternatively, at least one of the plurality of photometry areas may overlap an area subjected to a distance measuring.
Optionally, the green ligh
Hirai Isamu
Iida Yoshikazu
Adams Russell
Greenblum & Bernstein P.L.C.
Pentax Corporation
Smith Arthur A
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