Television – Camera – system and detail – With object or scene illumination
Reexamination Certificate
1999-10-05
2002-03-19
Garber, Wendy R. (Department: 2712)
Television
Camera, system and detail
With object or scene illumination
C348S229100, C348S296000, C396S166000
Reexamination Certificate
active
06359651
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. 10-284540 filed Oct. 6, 1998.
Japanese Patent Application No. 10-284541 filed Oct. 6, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic camera, and more specifically, it relates to an electronic camera which is capable of achieving color reproduction with a high degree of fidelity through flash photographing.
2. Description of the Related Art
Electronic cameras in the prior art include digital still cameras (hereafter in this specification, a “digital still camera” is referred to as a “DSC” in abbreviation). A DSC employs a solid imaging device such as a CCD or a CMOS sensor to capture an image of the image formed through a taking lens, i.e., performs A/D conversion on image data obtained through photoelectric conversion, compresses the data using an image compression algorithm such as JPEG as necessary and records the data in a non-volatile data storage device.
During the image-capturing operation described above, the exposure time at the solid imaging device is controlled by an electronic shutter. Namely, the exposure time is controlled by controlling the storage time at the solid imaging device instead of by opening/closing a mechanical shutter as in a camera that uses silver halide film (photographic film). As a result, high speed exposure times such as 1/4000 sec or 1/8000 sec can be realized with relative ease.
When taking a picture under back lighted conditions, e.g., when photographing a person standing in the shade of a tree against a background of ocean reflecting the sun, the difference between the brightness of the background and the brightness of the main subject, i.e., the person, is great and it is, therefore, difficult to perform photographing while achieving good exposure for both the background and the subject. In order to deal with this problem, a photographing method called the fill-flash photographing method has been proposed, whereby the shutter speed and the aperture are set so as to achieve the correct exposure for the background and compensating for the underexposure of the main subject by providing fill-in flash using an electronic flash unit.
However, when using fill-in flash as described above with a DSC, there may arise a situation in which the flash time at the electronic flash unit is approximately 1 msec while the shutter speed, i.e., the exposure time is set at a very small value of less than 1/1000 sec, depending upon the brightness of the background, the photographing distance from the camera to the main subject or the like. In such a case, the exposure ends before the light emission by the electronic flash unit is completed, which then results in lowered image quality due to underexposure of the main subject. In addition, it is a wasteful use of light emission energy for the electronic flash unit to keep emitting light even after the solid imaging device finishes exposure. Furthermore, if the electronic flash unit keeps emitting light even after the solid imaging device, finishes exposure and starts transfer of the electrical charge stored at the individual pixels at the solid imaging device, light that has been strongly reflected by a bright surface or the like in the subject may enter the charge vertical transfer unit of the solid imaging device to induce smearing, which will result in a poor image quality.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an electronic camera that makes it possible to prevent any reduction in the image quality occurring due to underexposure of the subject irradiated by an electronic flash unit even when the flash time is longer than the exposure time during a flash photographing operation.
A second object of the present invention is to provide an electronic camera that is capable of eliminating wasteful use of light emission energy at the electronic flash unit and preventing occurrence of smearing even when the flash time is longer than the exposure time during a flash photographing operation.
In order to achieve the objects described above, the electronic camera according to the present invention comprises an imaging device that performs photoelectric conversion of an image formed by a taking lens and outputs an image signal, an exposure time determination unit that determines the length of exposure time at the imaging device based upon the brightness of the subject, a light emission quantity control unit that controls the quantity of light emission by adjusting the length of flash time at an electronic flash unit when performing photographing using the electronic flash unit, an arithmetic operation unit that calculates the quantity of underexposure occurring when the length of flash time is longer than the exposure time and the exposure of the subject illuminated by the electronic flash unit is interrupted in the middle because of the shorter exposure time and a signal processing unit that generates image data by amplifying the image signal output by the imaging device at a specific gain and performed image processing by incorporating the quantity of underexposure calculated at the arithmetic operation unit at least either when engaging in gain adjustment or when engaging in color correction for image processing.
The present invention is further provided with a data table in which processing parameters corresponding to quantities of underexposure are stored, and the signal processing unit performs image processing based upon the processing parameters read out from the data table in correspondence to a given quantity of underexposure.
In addition, according to the present invention, the signal processing unit separates the image of the background from the image of the main subject and performs color correction in correspondence to the background and the main subject individually.
The electronic camera according to the present invention comprises an imaging device that performs photoelectric conversion of an image formed by a taking lens and outputs an image signal, an exposure time determination unit that determines the length of exposure time at the imaging device based upon the brightness of the subject, a light emission quantity control unit that controls the quantity of light emission by adjusting the length of flash time at an electronic flash unit when performing photographing using the electronic flash unit, and an exposure quantity control unit that ensures that the flash operation performed by the electronic flash unit is completed within the exposure time by reducing the length of flash time when the flash time is longer than the exposure time.
The present invention may further comprise a signal processing unit that engages in image processing on image data generated by amplifying the image signal output by the imaging device at a specific gain and an arithmetic operation unit that calculates the quantity of underexposure occurring as a result of the reduction in the flash time effected by the light emission quantity control unit. The signal processing unit uses the quantity of underexposure calculated at the arithmetic operation unit to engage in at least either gain adjustment or color correction through image processing.
The present invention is further provided with a data table in which processing parameters corresponding to quantities of underexposure are stored, and the signal processing unit performs image processing based upon the processing parameter read out from the data table in correspondence to a given quantity of underexposure.
In addition, according to the present invention, the signal processing unit separates the image of the background from the image of the main subject and performs color correction in correspondence to the background and the main subject individually.
The electronic camera according to the present invention comprises an imaging device that performs photoelectric conversion of an image formed by a taking lens and outputs an
Garber Wendy R.
Nikon Corporation
Oliff & Berridg,e PLC
Tillery Rashawn N
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