Photography – With exposure objective focusing means – focusing aid – or... – With electronic filtering
Reexamination Certificate
2002-12-09
2004-03-02
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
With electronic filtering
C396S128000
Reexamination Certificate
active
06701074
ABSTRACT:
This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2001-373989, 2001-377257 and 2002-30979 filed in JAPAN on Dec. 7, 2001, Dec. 11, 2001 and Feb. 7, 2002, respectively, 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 passive AF sensors.
2. Description of the Related Art
A distance measuring apparatus of a camera using an AF sensor in a passive method captures images of a distance measurement object by, for example, a pair of left and right line sensors, and obtains left and right sensor images (AF data). In the AF data obtained from the pair of left and right sensors, a pair of window ranges for obtaining a pair of AF data for use in a correlation value calculation are determined, and the pair of AF data for use in the correlation value calculation are sequentially obtained by shifting the pair of window ranges in the opposite directions in a pair of predetermined sensor areas (employed sensors). Otherwise, a pair of AF data for use in a correlation value calculation are sequentially obtained with one window range fixed, and another window range shifted. A distance from a distance measurement object is calculated according to a shift amount of the pair of window ranges when the highest correlation value (smallest minimum value) is obtained by obtaining the correlation of the obtained pair of AF data (i.e., when the left and right sensor images in the pair of employed sensors match each other) (refer to Japanese Patent Application Publication Nos. 8-285580 and 11-23957, and Japanese Patent No. 3099603, etc.).
When the highest correlation is obtained by a correlation value calculation of AF data as described above, the frequency of the correlation value calculations increases if the number of pixels of the AF data is large, thereby prolonging the distance measuring time.
Furthermore, when the distance from a distance measurement object is obtained as described above, and if the number of pixels of AF data becomes large, then the frequency of the correlation value calculations increases, thereby prolonging the distance measuring time. Therefore, Japanese Patent Application Publication No. 10-26525 discloses a distance measuring method in which discretely distributed pixels to be calculated are selected from the AF data, a correlation value calculation (uni-pixel correlation value calculation) is performed only on the selected pixels to be calculated, the correlation value of each pixel to be calculated is added for each shift amount, and the shift amount is obtained according to a total correlation value. Thus, the distance measuring time is shortened.
However, in the conventional distance measuring method, each correlation value is added for each shift amount after the uni-pixel correlation calculation of each pixel to be calculated. Therefore, there is the problem that all of the uni-pixel correlation calculations are to be stored.
Furthermore, a correlation value has conventionally been calculated for each shift amount while shifting the window range in a pixel unit, and the shift amount of the pair of window ranges when the highest correlation can be obtained from the calculated correlation value is determined. Therefore, if the number of pixels of an AF sensor becomes large, the frequency of the correlation value calculations increases, and the distance measuring time is prolonged.
Furthermore, in the distance measuring method described in the above-mentioned Japanese Patent Application Publication No. 10-26525, the distance measuring time can be shortened, but the distance measurement precision is reduced. Accordingly, to solve the problem, the following distance measuring method can be suggested. First, not all of the AF data in the window range are used, but the AF data at predetermined intervals of pixels (for example, each third pixel) is used to obtain the correlation value of a window range for each shift amount. When the highest correlation value (smallest minimum value) in the thus obtained correlation values is obtained, the shift amount is determined. At this time, the frequency of performing the correlation value calculation can be much lower than in obtaining the correlation value using all the AF data.
Then, the correct correlation value is calculated in the correlation value calculation using all AF data in the window ranges in predetermined ranges before and after the shift amount of the window ranges when the above highest correlation value is detected. The shift amount obtained when the highest correlation value is obtained in the correlation values thus calculated is determined, and the distance from the distance measurement object is calculated according to the shift amount. Thus, the distance measuring time can be shortened without reducing the distance measurement precision.
However, when the above-mentioned method is adopted, a false highest correlation value can be induced by the correlation values obtained from the AF data at predetermined intervals of pixels with a shift amount quite different from the shift amount of the true highest correlation value, since not all AF data are used. At this time, the true highest correlation value cannot be detected although a correct correlation value is calculated using all AF data before and after the shift amount of the false highest correlation value, thereby possibly making an erroneous measurement.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above-mentioned problems, and aims at providing a distance measuring apparatus which can shorten the distance measuring time without reducing any measurement precision, and prevent an erroneous measurement.
To attain the above-described object, the present invention is directed to a distance measuring apparatus, comprising: an AF data generating device which forms images of light from a distance measurement object on a pair of line sensors comprising a plurality of light-receiving elements and generates a pair of AF data for correlation value calculation according to signals obtained from the plurality of light-receiving elements; an AF data obtaining device which obtains a pair of AF data from a pair of employed sensor ranges for use in distance measurement in the pair of line sensors; a first correlation value calculating device which determines a pair of window ranges for obtaining the pair of AF data for use in the correlation value calculation in the pair of employed sensor ranges, and sequentially calculates correlation values while shifting the pair of window ranges to obtain a highest correlation value in the pair of employed sensor ranges, the first correlation value calculating device calculating the correlation values using AF data arranged at predetermined intervals in the AF data in the pair of window ranges; a second correlation value calculating device which sequentially calculates correlation values while shifting the pair of window ranges in predetermined ranges before and after a shift amount of the pair of window ranges when the highest correlation value in the correlation values obtained by the first correlation value calculating device is obtained, the second correlation value calculating device calculating the correlation values using all AF data in the pair of window ranges; and a distance measurement object distance calculating device which calculates a distance from the distance measurement object according to a shift amount of the pair of window ranges when the highest correlation value in the correlation values obtained by the second correlation value calculating device is obtained.
According to the present invention, the first correlation value calculating device can reduce the frequency of calculations in performing the correlation value calculation using the AF data at predetermined intervals in the AF data in the pair of window ranges while the second correlation v
Mihara Yoshikazu
Yoshida Hideo
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