JP2753544B2 - Focus detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detecting device for detecting a relative displacement of optical images of substantially the same object formed on a pair of photoelectric element arrays, respectively. In particular, it is used for a focus detection device such as a camera and a distance measuring device. 2. Description of the Related Art FIG. 1A shows an optical system of a focus detection device such as a general camera.
01 forms an image near the field lens 102. The primary image of the subject 100 is formed as a secondary image on the first and second photoelectric element arrays 105 and 106 by the first and second re-imaging lenses 103 and 104, respectively.
The relative positional relationship between the secondary images on the arrays 105 and 106 is detected from the image output of the arrays. [0003] Focus detection is performed from the relative positional relationship between the detected secondary images. [0004] When focus detection is performed in this manner, conventionally, focus detection is performed on only one portion of a subject, so that the places where focus detection can be performed are limited. Further, when there is no detectable subject in the detection area, focus detection cannot be performed. In order to avoid such a problem, if the focus detection area is widened, there is a problem that an object having a depth increases in one focus detection area and focus detection becomes impossible. The above problem is not limited to the pupil division type focus detection device shown in FIG. 1, but a device for photoelectrically detecting a pair of light images of the same object and performing distance measurement or focus detection from the relative position. This is common when target image displacement detection is performed.
An object of the present invention is to enable focus detection for a plurality of portions of a subject, and to consider the existence of the depth of the subject from the obtained plurality of image shift amount detection results, and to consider the intention of the photographer most. The purpose is to focus on the subject to be taken. In order to achieve this object, in the present invention,
As a first method, a subject closest to the camera is selected from a plurality of image shift amount detection results, and focusing is performed on the subject. Further, as a second method, the focus is set on a region that takes substantially the same value from the detection results of the plurality of image shift amounts, that is, a subject occupying a wide range. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, a pair of photoelectric element arrays 105 and 106 each including an image sensor such as a CCD are arranged in the photoelectric conversion unit 201 in parallel. An image of the same subject is formed on each photoelectric element array by the same focus detection optical system as in FIG. The image outputs a1... AN from the array 105 are sequentially A / D-converted by the A / D converter 202 in time series and stored in the data memory means 204 in the microcomputer 203. .., BN are also stored in the data memory means 204 via the A / D converter 202. The image shift calculating means 205 calculates the relative shift between the two image outputs, that is, the relative shift between the optical images on the pair of arrays, based on the pair of image outputs a 1... AN and b 1. Of course, the data used for the image shift calculation need not necessarily be the direct image output of the array, but may be an image output obtained by appropriately filtering or sampling these outputs. The correction data storage means 207 stores correction data for correcting the output of the image shift calculating means 205. This correction data is determined as follows.
That is, after the tentative adjustment of the focus detection optical system is completed during the manufacture of the focus detection device, the array 10 in the focused state is adjusted.
The relative displacement of each of the corresponding image points of the light images on the arrays 5 and 106 is measured, and the relative displacement of each of the image points on the array is stored in the storage means 207 as the correction amount. A specific example will be described. As shown in FIG. 1B, when the position of the array of photoelectric elements in the arrays 105 and 106 is x, and the center xo of the arrays 105 and 106 is the array 105, , 106 is relatively easy to adjust so that the corresponding image points of the light images on the center xo of the array coincide when focused. Therefore, when adjusted in this way, the relative positional deviation amount of each point has a characteristic S (x) indicated by a solid line at the focal point and a characteristic Z (x) at the out-of-focus state, as shown in FIG. Here, the characteristic S (x) at the time of focusing shows that the relative displacement amount at the array center xo is zero due to the above adjustment and increases linearly from here toward the periphery of the array. The focus characteristic Z (x) is translated from the characteristic S (x) by an amount ZT corresponding to the degree of out-of-focus. The focus shift S (x) is stored in the correction data storage unit 207. As a storage method, it is not preferable to store all the values of S (x) for each location x of the array because the number of stored data increases. Therefore, as shown in FIG. 3, when the displacement S (x) can be approximated by a straight line passing substantially through the origin xo, the displacement S (x) is determined only by the inclination of the straight line.
Since (x) can be specified, the storage means 207 may store data representing this inclination. In this case, the correction data storage means 207 can be extremely simplified, and as shown in FIG.
Adjustment may be made so as to represent the slope of (x), and the output of the potentiometer 401 may be input to the microcomputer 203 via the A / D converter 402. FIG. 4 shows the correction data storage means 207.
A ROM storing the above inclination as shown in FIG. In this ROM, each of the output terminals P1 to P8 is also connected to the power supply line Vcc and the ground line Et, and each of the output terminals P1 to P8 depends on the data to be stored.
Is connected to only one of the power supply line and the ground line. The correction data storage means 2
07, a ROM in the microcomputer 203 can be used. When the correction data S (x) is not a straight line but a curve as shown in FIG. 5, this curve is approximated by an n-th order equation, and this is specified by (n + 1) numerical values. I just need. Alternatively, correction data relating to several predetermined positions xi may be stored, and if correction data at an intermediate position is required, for example, Lagrange interpolation may be used. Returning to FIG. 2, the correction calculation means 206 corrects the output Z (x) of the image shift calculation means 205 with the correction data S (x) of the correction data storage means 207. Specifically, Z (x ) -S (x) is calculated to calculate the corrected image shift amount ZT. The corrected image shift amount ZT is converted into a defocus amount (a shift amount between a subject image and a predetermined image forming surface of the photographing lens) by the correction calculation unit 206 and sent to the display drive unit 208. This means 208 displays the focus adjustment state based on the defocus amount, and drives the taking lens to the in-focus position. This operation will be described below. A pair of arrays 1
AN, b1... B from the image outputs 05 and 106
N is stored in the data memory means 204 after A / D conversion. FIG. 6A illustrates the image outputs a1... AN stored in the data memory means 204. Image shift calculating means 2
In FIG. 5, for example, as shown in FIG. 6B or FIG. 6C, the image output includes five areas X-2, X-1, X0, X
1, X2, and image output b1.
Is also divided into five regions X-2, X-1, X0, X1, and X2, and a partial region Xi is obtained from the image output of each partial region X1.
, The partial image shift amount Z (xi) with respect to the center xi is calculated individually. The correction calculation means 206 calculates the partial correction amount S (xi) at the location xi from the contents of the correction data storage means 207. The partial correction amount S (xi) is obtained by substituting x = xi into the function S (x) as shown in FIG. Thereafter, the correction calculating means 206 subtracts the partial correction amount S (xi) from the partial image shift amount Z (xi), and obtains the corrected partial image shift amount Z (xi).
T (xi) is obtained. That is, ZT (xi) = Z (xi)-
Obtain S (xi). In this manner, the correction calculating means 206 obtains the corrected partial image shift amount ZT (xi) for each partial area Xi. For example, a simple average of these values 値 ZT (xi) / 5
Is calculated as a final image shift amount, which is converted into a defocus amount and sent to the display driving means 208. Although there are various methods for obtaining the final image shift amount ZT from the partial image shift amount ZT (xi) for each partial area Xi according to the purpose, some examples will be described below. (A1) Corrected partial image shift amount ZT (xi) as described above
Is the final image shift amount ZT. (A2) The average value of the remaining corrected partial image shift amounts excluding the maximum and minimum corrected partial image shift amounts ZT (xi) is defined as the final image shift amount ZT. (A3) The final image shift amount ZT is the center value when the corrected partial image shift amounts ZT (xi) are arranged in descending order. (A4) The corrected partial image shift amount ZT regarding the partial area where the information amount E (x) described later is the maximum is defined as the final image shift amount ZT. (A5) The final image shift amount Z is the average value of the corrected partial image shift amounts ZT (xi) for the plurality of partial regions having a relatively large information amount or the average value obtained by weighted addition according to the information amount.
Let it be T. As an algorithm for performing a partial image shift operation from the data of each partial area Xi, for example, a means for performing a Fourier transform of an image output and comparing phases (Japanese Patent Application Laid-Open No. 54-1979).
No. 104859) or means for performing a correlation operation to determine a shift amount that gives the maximum correlation (Japanese Patent Laid-Open No. 57-45510) can be used. When the number of photoelectric conversion elements included in the partial area Xi is small, it is better to use the Fourier transform method. When an object having a depth is imaged on the array, if the amount of image shift is calculated using the image output of the entire area of the array, it is completely unknown which part of the depth object is to be automatically focused. Becomes Such a problem relating to the depth subject can be solved as follows by calculating the partial image shift amount Z (xi) for each partial region Xi as described above. (B1) By selecting a partial image shift amount Z (xi) having the smallest image shift amount and calculating the final image shift amount ZT based on the selected partial image shift amount Z (xi), the defocus amount of the closest part of the depth subject can be obtained. On the contrary, the defocus amount for the distant portion can be obtained by selecting the one having the largest partial image shift amount, and the defocus amount for the intermediate distance portion can be obtained by selecting the intermediate one. (B2) If any of the plurality of partial image shift amounts Z (xi) has substantially the same value, the value is selected and the final image shift amount ZT is determined based on the value. Can be obtained. (B3) A partial image shift amount in a partial area Xi having the largest information amount described later is selected, and the final image shift amount ZT is determined based on the partial image shift amount.
Is obtained, it is possible to obtain a defocus amount for a subject having the largest amount of information for focus detection, generally a subject having the best contrast. Next, a specific example of calculating the partial image shift amount as described above will be described with reference to a flowchart. FIG.
In step, the partial image shift amount Z (xi) and the information amount E (xi) in each partial area Xi are calculated by the image shift calculating unit 205. Here, the information amount E (xi) represents the reliability of the corresponding partial image shift amount Z (xi), and the greater the value of this information amount, the higher the accuracy of the corresponding partial image shift amount. Specifically, if the image shift calculation is performed by phase comparison after Fourier transform as the information amount, values related to the amplitude after Fourier transform (r1, r1 'in JP-A-55-98710). , R2, r2 '
Is applicable. ) Can be used, and when the image shift calculation is a correlation method, an autocorrelation value Wm described later can be used. In the step, each of the partial areas Xi
Is compared with a predetermined threshold value Eth, and a partial area Xi of the information amount E (xj) having a value larger than the threshold value is selected. In the step, the correction data storage means 2
07, the partial correction amount S (xj) in the selected partial area xj is calculated, and the partial image shift amount Z (xj) in the selected partial area Xj is calculated as the partial image shift amount Z (xi ). In the step, the corrected partial image shift amount ZT (xj) for the selected area Xj is calculated as ZT (xj) =
It is determined from Z (xj) -S (xj). In the step, the corrected partial image shift amount ZT (x
j) is determined whether the variation is smaller than a predetermined value ΔZ, specifically, whether the difference between the maximum value and the minimum value of the corrected partial image shift amount ZT (xj) is smaller than a predetermined value. If the subject is small, the process proceeds to the step assuming that the subject has no depth. If not, the subject is determined to be a subject having the depth and the process proceeds to the step. In the step, for example, the above (A1)-
The final deviation amount ZT is obtained by any one of the processes (A5). In the step, for example, the above (B1) to (B3)
The final image shift amount ZT is obtained by any one of the above processes. The final image shift amount is converted into a defocus amount and displayed and driven. Since the image shift amount and the defocus amount are in a proportional relationship, a plurality of image shift amounts are converted into a plurality of defocus amounts, and the above comparison and selection are performed, and display and driving are performed based on the result. You may do it. Next, a description will be given of a correction method when the correction amount S (x) greatly changes in one detection area. FIG. 8A shows the data memory means 20 of FIG.
4 and a pair of data strings A1... AN, B1.
Is shown. This data string may be the image output of the photoelectric element array itself as described above, or an image output obtained by filtering or sampling the same. In FIG. 2, the image shift calculating unit 205 includes a pair of data strings A1 stored in the data memory unit 204.
.. AN, B1... BN, and one data string A1.
Are shifted by a predetermined amount with respect to the other data strings B1... BN, and the correlation amount C (L) for each shift amount L is obtained. That is, ## EQU1 ## The shift amount L at which the function C (L) is minimized
_m is obtained as an image shift amount. This image shift amount L _m as determined by the correlation calculation as contains errors due to insufficient adjustment of an optical system as described above, to correct the image shift amount L _m in the correction data S (x) There must be. However, this image shift amount is determined by the data sequence A1... AN, B1.
Since the calculation is performed from the entire region of N, there is a problem in which region of the correction data S (x) is used as the correction amount. This problem is solved as follows. The data strings A1... AN and B1... BN do not all contribute equally to the correlation amount C (L).
As shown in (a), the portion Y where the data sequence changes rapidly greatly contributes, and the portion where the change slowly changes has small contribution. That is, it depends on the contrast of each part. Therefore, the degree of the contribution (hereinafter referred to as contribution) for each location x of the data strings A1... AN, B1... BN is determined, and the correction amount is determined from the contribution correction data S (x) corresponding to this location. Good. The contribution W _m may be, for example determined from a difference between adjacent data in the data string. That is, W _m = | A _m −A _{m + 1} | or | B _m −B _{m + 1} |. The value W _m shown in Figure 8 (b). Of course, as W _m | A _m −A _{m + 1} | + | B _m −B _{m + 1}
| Can also be used. The correction amount ST is given by: Here, S _m is s when x = m.
(X). Therefore, the corrected image shift amount ZT is obtained from the following equation. ZT = L _m -ST Note that the positional deviation between the relative position between the first photoelectric element array and the optical image thereon and the relative position between the second photoelectric element array and the optical image thereon is dependent on the location. If the amount is extremely large, it may be difficult to correct the image shift amount with high accuracy using the correction data S (x). Therefore, by changing the pitch of the photoelectric elements of the first and second photoelectric element arrays in accordance with the location, the above-described positional shift amount is corrected to some extent in advance, and the remaining positional shift amount is stored as correction data. It is desirable to do. As described above, according to the present invention, focus detection is performed on a plurality of portions of a subject, and the depth of the subject is taken into consideration from the detection results of the obtained plurality of image shift amounts. Select the one closest to the photographer or the one that occupies a wide area, and then display the focus detection result or drive the photographing lens, so that the focus is on the subject considered to reflect the photographer's intention Can be combined.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is an optical diagram showing a relationship between a general focus detection optical system and a photoelectric element array. (B) is a front view showing a light image position on the photoelectric element. FIG. 2 is a block diagram showing one embodiment of the present invention. FIG. 3 is a graph showing an example of a relative displacement amount. FIGS. 4A and 4B are circuit diagrams showing a specific configuration example of a correction data storage unit. FIG. 5 is a graph showing another example of the relative displacement amount. FIG. 6A is a graph showing an example of an image output. (B) and (c) are figures showing a situation where an image output is divided into a plurality of areas. FIG. 7 is a flowchart showing a specific operation of the first embodiment. FIG. 8A is a graph showing another example of an image output. (B) is a graph showing the degree of change in image output. [Description of Signs of Main Parts] 105, 106: photoelectric element array 205: image shift calculation means 206: correction calculation means 207: correction data storage means

Claims (1)

(57) [Claims] (1) A pair of luminous fluxes that have passed through an area having parallax of the imaging optical system are re-imaged to form two images for focus detection on a focus detection sensor. For each of a plurality of different focus detection areas of the object field guided through the photographing optical system,
A focus detection optical system that forms an image; and a calculating unit that calculates a plurality of image shift amounts related to the plurality of focus detection regions from photoelectric outputs of the respective two images obtained from the focus detection sensor. A focus detection device that performs display or lens driving based on the image shift amount corresponding to the shortest distance among the image shift amounts. (2) A pair of light beams that have passed through the region having parallax of the photographing optical system are re-imaged to form two images for focus detection on a focus detection sensor, and an object field guided through the photographing optical system 2 for each of a plurality of different focus detection areas
A focus detection optical system that forms an image; and a calculating unit that calculates a plurality of image shift amounts related to the plurality of focus detection regions from photoelectric outputs of the respective two images obtained from the focus detection sensor. A focus detection device which selects one that takes a plurality of substantially equal values from among the image shift amounts and performs display or lens driving based on the final image shift amount as a final image shift amount.