Television – Camera – system and detail – With single image scanning device supplying plural color...
Reexamination Certificate
1999-10-26
2003-12-09
Moe, Aung S. (Department: 2612)
Television
Camera, system and detail
With single image scanning device supplying plural color...
C348S360000, C348S335000, C348S272000
Reexamination Certificate
active
06661458
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image pickup apparatus and an image pickup apparatus system. More particularly, the present invention relates to a compact and low-cost image pickup apparatus that is capable of photographing high-quality images comparable to silver halide photographs and also capable of obtaining photographic effects equivalent to those which are available for silver halide photographs, e.g. utilization of blurring and cropping.
There are digital cameras designed for business use, e.g. printing, which are capable of obtaining images comparable in quality to photographs. In many of these digital cameras, the pixel pitch of the image pickup device is about 10 micrometers or more, and the number of pixels is 2 million or more. The size of the image pickup device is the APS size or larger in terms of the size of silver halide film. Many of these digital cameras use an optical system developed for conventional silver halide photography.
In these image pickup apparatuses, the correlation between the depth of field and the field angle is close to that in silver halide photography because they use an image pickup device having a format size close to that of silver halide film. Therefore, it is possible to obtain photographic effects equivalent to those which are available for silver halide photographs, e.g. utilization of blurring associated with the depth of field.
However, image pickup devices used in these image pickup apparatuses are relatively large in size. Therefore, there is a limit to the number of devices obtained from one wafer. Consequently, the cost cannot be reduced in excess of a certain limit.
In addition, because optical systems used for photography are those developed for the conventional silver halide photography, no consideration is given to problems inherent in apparatuses using an image pickup device, for example, the deterioration of image information due to the fact that the aperture portion has a fixed size and the integral of the amount of light entering the aperture portion becomes an image signal, and the effect of filters such as an optical low-pass filter for removing moire and an infrared cutoff filter for eliminating adverse effects of infrared rays on the image, and further the effect of the physical structure of the image pickup device on the image.
In the case of silver halide film, a color image is made up of layered portions that form C, M and Y color images, respectively. In the case of an electronic image pickup device, because a plurality of color images cannot separately be formed in one pixel, the common practice is to employ a method in which a plurality of photographing operations are carried out for each color, and color images thus obtained are combined together afterward, or a method in which a plurality of images of different colors are formed with a plurality of image pickup devices provided for a plurality of branched optical paths, or a method in which color filter elements are arrayed in a matrix over the image pickup surface of an image pickup device, and pixels are associated with the respective colors of the filter elements, and in which an intensity concerning a color other than the associated filter colors is obtained by a computation from surrounding pixels or other technique.
The first method has the problem that a moving object cannot be photographed because it takes time to take a photograph. The second method has the problem that the cost increases because it requires a plurality of image pickup devices and a member for branching the optical path, and the apparatus becomes unfavorably large in size because the optical path branching member is inserted between the optical system and the image pickup devices. Accordingly, to realize a compact and low-cost apparatus, it is desirable to employ the third method.
In this case, the matrix filter array requires a certain thickness because it is necessary to impart a specific spectral transmittance to each filter element. Moreover, it is impossible to infinitely narrow the spacing between the filter array and the photoelectric conversion surface because of the electrode structure and the method of forming the photoelectric conversion surface.
Accordingly, if light is incident on the image pickup device extremely obliquely, light passing through a filter element enters a photoelectric conversion surface region other than the one that is associated with this filter element and where the light should arrive. This makes it impossible to obtain color information accurately.
It is also conceivable to form an infrared cutoff filter and color filters from interference filters that utilize a dielectric multilayer film, thereby minimizing the thickness of the filters. However, such an interference filter involves the problems that the transmittance varies according to the incident angle of light because the interference filter performs its function on the basis of the optical path length of light passing through the filter.
Accordingly, in the case of an apparatus using a image pickup device, it is desirable that the angle at which light exiting from the optical system is incident on the image pickup device, particularly the incident angle of the principal ray, should be minimized.
However, there is no severe restriction on the exit angle of optical systems designed for silver halide photography. Therefore, the image pickup apparatus cannot use any of the optical systems lined up for silver halide photography.
Incidentally, the most effective way of reducing the production cost of image pickup devices is to reduce the device size so that an increased number of devices are obtained from one wafer.
Many of image pickup apparatus that have been commercially manufactured as relatively low-cost apparatus use image pickup devices of ⅓ to ⅔ inch size and with about 1 to 2.5 million pixels.
The pixel pitch of these image pickup devices is about 3 to 5 micrometers, which is markedly small in comparison to image pickup devices used in the above-described digital cameras for business use. It is known that if the number of pixels is further increased to attain image quality comparable to that of silver halide photographs by using an image pickup device of the above-described size, the pixel pitch also inevitably decreases, so that it becomes impossible to ignore the reduction in sensitivity of the image pickup device and the degradation of image quality caused by shot noise arising from the photon number fluctuation.
These image pickup apparatuses use an optical system optimally designed to exhibit the characteristics of the image pickup device used. Therefore, many of them are designed by giving full consideration to the above-described problems associated with the use of an image pickup device.
On the other hand, it is known that as the area of the image pickup device decreases, the focal length of the optical system becomes shorter, and the optical depth of field becomes greater, giving rise to problems which are unlikely to occur in the case of taking silver halide photographs using a 35-mm film or the like.
For example, even when it is intended to take a picture in which a person is imaged large and sharply in an unsharp background as in portrait photography, such a phenomenon may occur that the background does not become unsharp as intended, or dust or falling snow or the like between the subject and the photographer which the photographer does not recognize is clearly imaged undesirably by photography using an electronic flash.
To solve these problems, it is conceivable to use an optical system with a small F-number or to lengthen the focal length to thereby reduce the depth of field. However, with the former method, the optical system becomes large in size, and the number of lens elements constituting the optical system increases, causing the cost to increase. With the latter method, because the photographing field angle changes, there are cases where the photographer's intended composition of a picture cannot be obtained. Accord
Takada Katsuhiro
Takeyama Tetsuhide
Moe Aung S.
Olympus Optical Co,. Ltd.
Ye Lin
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