Optics: measuring and testing – Range or remote distance finding – Triangulation ranging with photodetection – but with no...
Reexamination Certificate
2003-02-25
2004-07-27
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
Triangulation ranging with photodetection, but with no...
C250S201600, C250S201800, C356S003150, C396S128000
Reexamination Certificate
active
06768540
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase difference detection method, a phase difference detection apparatus, a range finding apparatus and an imaging apparatus.
2. Description of the Related Art
In a conventional automatic focusing camera and the like, when focusing on an object to be photographed by use of a so-called passive system, in case of a non-TTL camera, the distance to the object is detected by use of an image of the object which does not pass through a taking lens. Thereafter, a position of the taking lens is controlled in response to the detected distance to the object. In the case of a TTL camera, a shift amount from a focused state is detected by use of an image of the object obtained through the taking lens. Thereafter, the rotational position of the taking lens is controlled in response to the detected shift amount. The principle of the above-described series of operations will be described below with reference to FIG.
3
A.
As shown, a pair of lenses
1
a
and
1
b
are disposed apart from each other by a predetermined base line length b, and images of an object
2
are respectively formed through optical paths A and B which are different from each other on a pair of optical sensor arrays
3
a
and
3
b
which are disposed apart from the pair of lenses
1
a
and
1
b
by a focal distance f. It is assumed that the object
2
is located at a position in front of the pair of lenses
1
a
and
1
b
by a distance L.
When the object
2
is located at a distance L of infinity, centers of the images formed on the pair of optical sensor arrays
3
a
and
3
b
are formed at reference positions (
3
a
1
,
3
b
1
) on the optical sensor arrays
3
a
and
3
b
which correspond to optical axes of the lenses
1
a
and
1
b
. However, when the object
2
is closer than a distance of infinity, the images are formed at positions which are shifted by an amount (from reference positions
3
a
1
,
3
b
1
). Based on the principle of triangular ranging, the distance L to the object
2
equals bf/&agr;. Here, since the base line length b and the focal distance f are constants, if the shift amount &agr; is detected, the distance L can be calculated. This is the principle of passive ranging (so-called outside light triangular ranging), which is used in the non-TTL camera. In the non-TTL camera, the shift amount a may be used as it is for calculation purposes instead of using the distance L as an output value of a range finding apparatus.
In case of the TTL camera, by applying a light passed through an imaging lens (not shown) to the pair of lenses
1
a
and
1
b
in the same manner as described above, the shift amount &agr; between a pair of left and right images is detected. In this case, it is assumed that centers of images in case of a focused state are reference positions on the respective optical sensor arrays
3
a
and
3
b
. Thus, positive and negative values of the shift amount &agr; indicate a front focus state and a rear focus state, respectively, and the absolute values thereof indicate an extent of the shift from in-focus. In addition, in the present specification, the shift amount a&agr; is referred to as a phase difference.
In any of the cameras described above, the image of an object to be photographed is formed on the pair of optical sensor arrays by an optical system, and a relative shift of the pair of image signals output by the pair of optical sensor arrays, i.e., the phase difference, is detected by carrying out a process known as correlation calculation about partial image data groups (see
FIG. 3B
) extracted from the pair of image signals, respectively. In addition, phase difference detection as described above is not limited to automatic focusing cameras but can be used for various range finding apparatuses, focal point detection apparatuses, and the like, which measure the distance to an object or focus on an object.
In an apparatus which uses phase difference detection as a method for reducing degradation of detection accuracy due to the presence of a back-light from strong light sources such as the sun, which serve as a background of an object to be photographed (at a time of so-called back-light), there is one such device which is described, for example, in Japanese Patent No. 3,230,759 (JP-A-5-264892). More specifically, it is judged whether or not there is an effect of a flare light acting as a back-light on the output of an optical sensor. When it is judged that there is an effect of a flare light, a compensation value based upon a difference in light intensities of the pair of the image signals and, more particularly, based on a difference in average values of respective image signals, is calculated. The calculated compensation value is added to or subtracted from one of the image signals. The phase difference is then calculated by carrying out the correlation calculation based upon the image signal after performing such compensation.
However, the effect caused by a back-light is fairly complicated, and even if a predetermined compensation routine is carried out to correct the image signal as described above, the effect of the back-light is not necessarily removed. For example, when the pair of image signals take on the states shown in
FIGS. 4A and 4B
due to the presence of a back-light, even if the compensation value is determined based upon the difference in light intensities of the pair of image signals in the manner described above and compensation is performed by adding or subtracting the calculated compensation value to or from one of the image signals, it becomes difficult to remove the effect of the back-light from the image signal. Accordingly, in the technology described in the above U.S. Pat. No. 3,230,759 (JP-A-5-264892), there is a possibility that a non-productive compensation is carried out.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a phase difference detection method, a phase difference detection apparatus, a ranging (or range finding) apparatus, and a imaging apparatus which can reduce the possibility of non-productive compensation.
A phase difference detection method in accordance with a first aspect of the present invention comprises a judgment step of judging whether or not a predetermined compensation would be effective on an image data row which is generated in response to outputs of a pair of optical sensor arrays on which images of a measurement image object are formed, a first phase difference detection step of detecting a phase difference between the images formed on the pair of sensor arrays based upon the image data row when it is judged that the predetermined compensation would not be effective, and a second phase difference detection step of carrying out the predetermined compensation with respect to the image data row when it is judged that the predetermined compensation would be effective and of detecting a phase difference between the images formed on the pair of sensor arrays based upon the image data row after performing the predetermined compensation.
By the foregoing method, when it is judged that the predetermined compensation would not be effective based upon the image data row, the phase difference between the images formed on the pair of sensor arrays is detected, and when it is judged that the predetermined compensation would be effective, the predetermined compensation is applied to the image data row and, based upon the compensated image data, the phase difference of the images formed on the pair of sensor arrays is detected. Thus, it becomes possible to reduce the occurrence of unproductive compensation.
In accordance with a second aspect of the present invention, the predetermined compensation is deemed effective when, based upon the image data row, an output waveform of one of the pair of optical sensor arrays is shifted in parallel with respect to an output waveform of one the other optical sensor array, and the compensation is based upon the amount of the shift. Accordingly, in addition to the above-described advantag
Adams & Wilks
Buczinski Stephen C.
Seiko Precision Inc.
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