Television – Camera – system and detail – Optics
Reexamination Certificate
1997-06-13
2001-01-30
Garber, Wendy (Department: 2712)
Television
Camera, system and detail
Optics
C348S345000, C348S349000
Reexamination Certificate
active
06181378
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image reading device having an automatic focusing function.
In a camera-type image reading device, since the distance between the image reading device and an object varies, data related to the distance should be obtained in order to focus on the object.
In the field of photography in which a camera uses a film, an active and passive distance measuring method are well known. In the active method, an infrared light is emitted from the camera to the object, and by detecting the reflected infrared light, the distance is measured. In the passive method, by detecting a phase difference of an object image, or detecting a distribution of contrast information of the object, the distance or defocus amount is detected. In such a camera, an automatic focusing mechanism is provided, which moves a focusing lens in accordance with the detected object distance or the defocus amount so that an in-focus image is formed on a film plane.
Specifically, when the phase difference of the object image is detected, a pair of separator lenses are provided to form a pair of images to be compared with each other. When the contrast distribution is detected, a half mirror is used to split the light from the object, and the contrast distribution on planes which have different optical distances from a focusing lens.
In the image reading device using an image sensor, such as a CCD (Charge Coupled Device) to capture an object image, since the optical image is converted into a digital data which can be processed by a microprocessor or the like easily, it is preferable that the focus condition is detected with use of the image sensor. However, the conventional methods mentioned above cannot be applied to the image capturing system, and therefore, in order to employ the conventional focusing system, an extra optical system should be introduced in the image reading device.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved image reading device which is capable of detecting a focusing condition using the image sensor which is used for capturing the image.
According to one aspect of the invention, there is provided an image reading device that includes: a focusing lens for forming an image of an object; a linear image sensor for capturing the image, the image sensor including a plurality of image receiving elements arranged in a line along a predetermined direction, the plurality of image receiving elements outputting image signals corresponding to the image; a contrast detecting system which detects contrast data representative of a contrast of the image based on the image signals; a rotatable mirror arranged between the object and the focusing lens, the rotatable mirror being rotatable about an axis parallel to the predetermined direction and reflecting light from the object towards the focusing lens; a driving mechanism which moves at least one of the focusing lens and the image sensor to change a distance therebetween; and a focusing condition judging system which, while controlling the contrast detecting system to detect the contrast data and controlling the driving mechanism to move the at least one of the focusing lens and the image sensor, determines an in-focus condition of the image in accordance with the contrast data.
In a particular case, the focusing condition judging system controls the contrast detecting system to periodically detect the contrast data during the movement of at least one of the focusing lens and the image sensor and judges whether the in-focus condition is obtained in accordance with a change in the contrast data.
In another particular case, the focusing condition judging system judges that the in-focus condition is obtained when the contrast data has a maximum value.
In yet another particular case, the focusing condition judging system controls the driving mechanism to periodically move at least one of the lens and the image sensor by a predetermined unit amount, and controls the contrast detecting system to detect the contrast data for each movement of at least one of the focusing lens and the image sensor. The focusing condition judging system also determines that the in-focus condition is obtained when a current contrast data is less than a previous contrast data.
In still another particular case, the focusing condition judging system controls the driving mechanism to periodically move at least one of the lens and the image sensor by a predetermined unit amount, and controls the contrast detecting system to detect the contrast data for each movement of at least one of the focusing lens and the image sensor. In this case, the focusing condition judging system may determine that the in-focus condition is obtained when the contrast data is substantially a maximum.
In still another particular case, the contrast data is a difference between a maximum brightness image signal and a minimum brightness image signal.
In still another particular case, the contrast data is a sum of a difference of image signals for adjacent light receiving elements.
In still another particular case, the focusing condition judging system controls the driving mechanism to move at least one of the focusing lens and the image sensor through a predetermined range, and controls the contrast detecting system to detect the contrast data periodically during the movement, such that the focusing condition judging system determines the in-focus condition based on a maximum of the contrast data.
In still another particular case, the contrast data is an average of a plurality of contrast measurements performed at a single position of the driving mechanism.
In still another particular case, the predetermined range is divided into a plurality of sub-ranges, and the contrast data is an average of a plurality of contrast measurements performed at a predetermined number of positions of the driving mechanism within each of the sub-ranges, and the focusing condition judging system determines the in-focus condition also based on the sub-ranges.
In still another particular case, the focusing condition judging system controls the driving mechanism such that the imaging lens is moved from a farthest position farthest from the image sensor to a nearest position nearest to the image sensor.
In still another particular case, the image reading device may be further provided with a projecting unit for projecting a contrast pattern towards the object, and the image reading device may operate such that, if the focusing condition judging system fails to detect an in-focus condition, the projecting unit is turned ON and the focusing condition judging system is operated again.
In this case, when the imaging lens and the image sensor are located a maximum distance apart, the focusing condition judging system controls the contrast detecting system to detect projecting unit contrast data when the projecting unit is ON, compares the projecting unit contrast data with the contrast data, and determines that the in-focus condition is obtained if the projecting unit contrast data and the contrast data match.
Further, if the projecting unit contrast data and the contrast data do not match, the focusing condition judging system controls the driving mechanism to move at least the imaging lens or the image sensor such that the imaging lens and the image sensor move closer together while detecting an in-focus condition based on the contrast data.
In still another particular case, the image reading device may be further provided with a projecting unit for projecting a contrast pattern towards the object and the projecting unit is turned ON during operation of the focusing condition judging system.
In still another particular case, the focusing condition judging system further controls the rotatable mirror such that, if the in-focus condition is not obtained, the rotating mirror is rotated until the contrast detecting system detects a change of the contrast data.
In this case, it the change of the contrast data is detected, the focusing condition judging s
Horie Mikio
Suzuki Minoru
Asahi Kogaku Kogyo Kabushiki Kaisha
Christensen Andrew B.
Garber Wendy
Greenblum & Bernstein P.L.C.
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