Photography – With exposure objective focusing means – focusing aid – or... – Reliability of focus/distance signal
Reexamination Certificate
2002-12-10
2004-12-07
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Reliability of focus/distance signal
C396S121000, C396S128000, C396S147000
Reexamination Certificate
active
06829434
ABSTRACT:
This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2001-375737 and 2001-377259 filed in JAPAN on Dec. 10, 2001 and Dec. 11, 2001, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distance measuring apparatus, and particularly to a distance measuring apparatus of, for example, a camera using a passive AF sensor.
2. Description of the Related Art
A distance measuring apparatus of a camera using a passive AF sensor forms images of a distance measurement object on a pair of left and right line sensors, for example, and obtains left and right sensor images (AF data). A pair of window ranges for obtaining a pair of AF data for use in correlation value calculation, of AF data obtained from the pair of left and right line sensors, are determined, and the pair of AF data for use in correlation value calculation are sequentially obtained, with the pair of window ranges being shifted in opposite directions in a pair of predetermined sensor areas (employed sensors). Alternatively, a pair of AF data for use in correlation value calculation are sequentially obtained, with one window range being fixed and the other window range being shifted. The correlation level of the thus obtained pair of AF data is determined, and the distance from the distance measurement object is calculated according to the shift amount of the pair of window ranges providing the highest correlation level (in which left and right sensor images are consistent with each other) (refer to Japanese Patent Application Publication Nos. 8-285580 and 11-23957, and Japanese Patent No. 3099603).
A shift amount of the pair of window ranges providing the minimum value of correlation values determined for the shift amounts of the pair of window ranges is generally considered as the shift amount of the pair of window ranges providing the highest correlation level. There are cases where a plurality of minimum values exist, and in these cases, the shift amount of the pair of window ranges providing the smallest minimum value is considered as the shift amount of the pair of window ranges providing the highest correlation level. Furthermore, for some methods of calculating correlation values, the maximum correlation value may correspond to the highest correlation level, but the following description is based on the assumption that the minimum correlation value corresponds to the highest correlation level.
There are cases where a plurality of minimum values exist, and in these cases, the shift amount of the pair of window ranges providing the smallest minimum value is determined to be the shift amount of the pair of window ranges of the highest correlation. However, in the case where the difference (hereinafter referred to as difference of minimum values) is small between the shift amount of the pair of window ranges with the smallest minimum value and the shift amount of the pair of window ranges with the second minimum value that is the second smallest minimum value, erroneous distance measurement may occur if the shift amount of the pair of window ranges with the smallest minimum value is determined to be the shift amount of the pair of window ranges of the highest correlation, and therefore it is preferably determined that distance measurement is impossible. Furthermore, determination on reliability of distance measurement is described in, for example, Japanese Patent Application Publication No. 2000-193879.
However, there are cases where it should be determined distance measurement is possible even if the difference between the smallest minimum value and the second minimum value is somewhat small, and where it should be determined that distance measurement is impossible even if the difference of the minimum values is somewhat large; and hence, it is not appropriate to determine whether distance measurement is possible or impossible according to whether the difference of the minimum values is smaller than a fixed threshold or not.
For the former aspect, for example, AF data in the employed sensor has low contrast. In this case, the correlation values calculated by the correlation value calculation are generally small, and therefore the difference of the minimum values is small. However, distance measurement is possible unless the difference of the minimum values is extremely small. For the latter aspect, on the other hand, AF data in the employed sensor has high contrast and changes periodically. Such AF data is obtained, for example, when a distance measurement object having a striped pattern is imaged. In this case, the correlation values calculated by correlation value calculation are changed periodically and are generally large, and therefore the difference of the minimum values is large. However, it should be determined that distance measurement is impossible because there is a high possibility that erroneous distance measurement occurs even if the difference of the minimum values is larger than the fixed threshold except that the difference of the minimum values is extremely large.
Therefore, when determining whether distance measurement is possible or impossible according to the difference of the minimum values, the possibility of erroneous distance measurement becomes higher as in the latter aspect if the threshold is set at a lower level, and the possibility that it is determined that distance measurement is impossible more than necessary becomes higher if the threshold is set at a higher as in the former aspect.
On the other hand, if the distance measurement object is located at a distance shorter than the closest distance where distance measurement is possible, no minimum value exists essentially, but there may be cases where a minimum value actually exists. In this case, the shift amount of the pair of window ranges providing the minimum value is determined to be the shift amount of the pair of window ranges providing the highest correlation level, and the distance from the distance measurement object is calculated according to the shift amount of the pair of window ranges, resulting in erroneous distance measurement.
Therefore, it is conventionally determined that distance measurement is impossible if the minimum value is larger than a predetermined reference value even when the minimum value exists, so that problems such that the distance from the distance measurement object is calculated with a minimum value not suitable as highest correlation are prevented.
In the conventional method, however, erroneous distance measurement where the distance measurement object is located at a distance shorter than the closest distance cannot be thoroughly prevented. For example, in the case where the distance measurement object is located at a distance shorter than the closest distance, and the contrast of the sensor image is low, there may exist an extremum smaller than the reference value for determining that distance measurement is impossible, and in this case distance measurement is carried out according to the shift amount of the pair of window ranges providing the extremum, and it is not determined that distance measurement is impossible.
In this way, in the case where the distance measurement object is located at a distance shorter than the closest distance, and a minimum value exists, a correlation value smaller than the minimum value exists on the side of the close distance. Moreover, a correlation value smaller than the minimum value may exist on the side of the infinite distance even if the distance measurement object is located in the range where distance measurement is possible. In this case, because it can be considered that something abnormal has occurred, erroneous distance measurement may occur as in the above-described case if the distance from the distance measurement object is calculated according to the shift amount of the pair of window ranges providing the minimum value.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above situations, and the object t
Mihara Yoshikazu
Yoshida Hideo
Birch & Stewart Kolasch & Birch, LLP
Perkey W. B.
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