Television – Camera – system and detail – With object or scene illumination
Reexamination Certificate
1999-08-27
2004-06-22
Vu, Ngoc-Yen (Department: 2612)
Television
Camera, system and detail
With object or scene illumination
C348S364000
Reexamination Certificate
active
06753920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic camera for producing an image having a wide dynamic range by composing or synthesizing two image signals obtained by picking-up an object two times with a desired exposure amount ratio with the aid of a single solid state image sensing element, and more particularly to an electronic camera for producing a composed image having a wide dynamic range as well as a high quality by utilizing a flash light emitting device, e.g. stroboscopic flash device. Such an electronic camera is generally called a filmless digital still camera.
2. Description of the Related Art
In the electronic camera, use is generally made of a solid state image sensing element such as CCD image sensing element. It is well known that such a solid state image sensing element is liable to be saturated with a relatively low luminance and has a low S/N for a lower luminance. Therefore, there is a problem that a dynamic range of the solid state image sensing element is very narrower than a conventional photographic film.
In order to solve such a problem, there has been proposed an electronic camera, in which an image having an extended dynamic range is obtained by composing two image signals which are produced by a single solid state image sensing element when an object is picked-up with different exposure amounts two times successively. For instance, in Japanese Patent Application Laid-open Publication Kokai Hei 4-207581, there is disclosed an electronic camera, in which immediately after transferring signal charges stored in a light receiving section of a solid state image sensing element during a first exposure into a transfer section of the element, a second exposure having a longer exposure time than the first exposure is initiated, and signal charges stored in the light receiving section during the second exposure are transferred into the transfer section after the signal charges of the first exposure have been outputted from the solid state image sensing element. In this manner, the second exposure can be performed for a time interval during which the signal charges produced by the first exposure and transferred into the vertical transfer section are read out of the solid state image sensing element, and therefore it is possible to obtain two image signals with a short time interval. Then, the thus obtained two image signals are composed to derive a composed image having a wider dynamic range.
Further, in Japanese Patent Application Laid-open Publication Kokai Sho 62-108678, there is disclosed an electronic camera, in which upon producing an image with a wide dynamic range by composing two image signals obtained with different exposure amounts, one of the image signals is obtained by picking-up an object under the natural light, and the other image signal is obtained by picking-up the same object with a stroboscopic flash light, and these image signals are compared with each other to extract image portions having a larger amplitude to obtain a composed image.
In general, when an object has a lower luminance level, the image is picked-up with stroboscopic flash light. However, in case of obtaining an image with a wide dynamic range by composing two image signals obtained with different exposure amounts, when one of the image signals is obtained with the natural light and the other image signal is obtained with the flash light and the thus obtained two image signals are merely composed, it is difficult to obtain the two image signals with a desired exposure amount ratio in a highly precise manner although exposure times are set accurately owing to the fact that stroboscopic flash light fluctuates largely.
Furthermore, when the stroboscopic flash light is used, a portion of an object which is irradiated with the stroboscopic flash light can be picked-up such that the image signal with the stroboscopic flash light can have the given exposure amount ration with respect to the image signal with the natural light, but at apportion of the object which is not irradiated with the stroboscopic flash light, only the image signal with a same exposure amount as that with the natural light is obtained by the second exposure, and therefore there is a problem that the image picking-up operations could not be conducted with a desired exposure amount ratio between the first and second shots. Moreover, since a white balance of the image signal with the natural light differs from that with the stroboscopic flash light, when the image signals are composed, a color balance might be partially lost.
In order to solve the above mentioned problems, there has been proposed an electronic camera, in which first and second image picking-up operations are carried out successively with stroboscopic flash light to produce two image signals, and the thus obtained two image signals are synthesized to form a composed image. When both the two image signals to be composed are derived with the stroboscopic flash light, it is easy to perform the first and second image picking-up operations with a desired exposure amount ratio over a whole image area, and therefore it is possible to obtain a composed image having a wide dynamic range and having a uniform white balance over a whole image.
In this case, there may be provided two sets of stroboscopic flash devices each comprising a Xenon tube, a trigger capacitance and a light emission capacitance, these stroboscopic flash devices are alternately used for the first and second exposures. However, it is apparent that the electronic camera including such a system is liable to be high in cost, large in size and heavy in weight. Therefore, it is desired that the two image picking-up operations are performed by means of a single stroboscopic flash device which is used in a conventional camera in which no image signal composition is carried out.
In this case, when the stroboscopic flash device is operated for the two exposures like as the conventional stroboscopic flash exposure, i.e. when the trigger capacitance is charged and a trigger voltage is applied to the Xenon tube each time the stroboscopic flash exposure is carried out, two image signals could not be obtained with a short time interval. This is due to the fact that in general, the trigger capacitance is charged through a resistor, and therefore a relatively long time period such as 6 msec is required for the trigger capacitance due to a time constant of the triggering circuit until the trigger capacitance is charged up to an effective trigger voltage. This results in that the second exposure could not be initiated immediately after the completion of the first exposure. In this manner, a relatively long time interval is required from the end of the first exposure to the start of the second exposure. This affects the second exposure and its shutter speed, and particularly when the object includes a moving subject, a portion of the composed image corresponding the relative movement might be deteriorated. In case of the color image, false color or false contour might be produced.
Moreover, when the second exposure is performed by applying the electrostatic charge stored in the trigger capacitance as the trigger voltage to the Xenon tube like as the conventional stroboscopic flash exposure, the trigger voltage having an amplitude of several KVs might produce undesired noise, and if this second triggering period overlaps with the storing period or transferring period of the signal charges of the first exposure, the image signal obtained with the first exposure might be deteriorated.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a novel and useful electronic camera, which can solve the above mentioned problems and can produce a composed image having a high quality and a wide dynamic range by conducting first and second exposures with flash light.
According to the invention, an electronic camera producing an image having a wide dynamic range by composing two image signals obtained by picking-up an object two times successively
Fukuda Hidetoshi
Inagaki Osamu
Kakinuma Minoru
Koseki Hiroaki
Momose Takumi
Olympus Optical Co,. Ltd.
Stevens, Davis, Miller & Mosher, LLP.
Vu Ngoc-Yen
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