JP4821521B2 - Focus adjustment apparatus and method - Google Patents

Description

  The present invention relates to a focus adjustment apparatus and method.

  The defocus amounts detected in multiple focus detection areas are grouped into groups that can be seen as the same subject, and the group that seems to best match the photographer's intention is selected and selected from the multiple groups. There is known a focus adjustment device that determines the final defocus amount by performing a statistical average among the groups (for example, see Patent Document 1).

Prior art documents related to the invention of this application include the following.
Japanese Patent Laid-Open No. 02-178641

  If the contrast of the subject image in the focus detection area is low, a highly reliable defocus amount cannot be obtained. Therefore, in the grouping process, focus detection areas with low defocus amount reliability are not included in the group. However, if the photographic lens is largely out of focus, even if the subject itself is high in contrast, the contrast of the subject image in the focus detection area will be low and the focus detection area will be excluded from the group, so it can be regarded as the same subject. There is a problem in that the grouping process for combining a plurality of defocus amounts into one group cannot be performed correctly, and the focus adjustment for the subject intended by the photographer cannot be performed.

According to a first aspect of the present invention, there is provided a focus adjustment apparatus including: a detection unit that detects a defocus amount for each of a plurality of focus detection areas of an object field; and each of the plurality of defocus amounts detected by the detection unit determines reliability. extraction means for extracting a determination unit configured to determine whether or above the threshold, a plurality of defocus amounts is determined that the reliability determination threshold value or more by the determining means, a plurality of de extracted by the extraction means Determining means for determining a final defocus amount based on the focus amount ; driving means for driving the photographing lens based on the final defocus amount determined by the determining means; the detecting means; the determining means; and the extracting means. , and a repeat that perform control means a series of focus adjustment operation by the determining means and the drive means, in the first focusing operation, the detection hand Detects a plurality of first defocus amounts corresponding to the plurality of focus detection areas, and the determination means determines whether the plurality of first defocus amounts is equal to or greater than a first reliability determination threshold value. And the extraction means extracts a plurality of first defocus amounts determined by the determination means to be equal to or higher than the first reliability determination threshold value, and the determination means is determined by the extraction means. A first final defocus amount is determined from the extracted first defocus amounts, and the driving unit drives the photographing lens based on the first final defocus amount, and the first defocus amount is determined. In the second focus adjustment operation subsequent to the driving of the photographing lens based on the final defocus amount, the detection means detects a plurality of second defocus amounts corresponding to the plurality of focus detection areas, and Judgment means It is determined whether or not the plurality of second defocus amounts are equal to or higher than a second reliability determination threshold value that is higher than the first reliability determination threshold value. A plurality of second defocus amounts determined to be equal to or greater than a second reliability determination threshold value are extracted, and the determination unit sets the plurality of second defocus amounts extracted by the extraction unit to a plurality of second defocus amounts. A grouping process to divide the group, a final group is selected from the plurality of groups, a second final defocus amount is determined using a defocus amount of the selected final group, and the driving unit Is characterized in that the photographing lens is driven based on the second final defocus amount .
According to a third aspect of the present invention, there is provided a focus adjustment method for detecting a defocus amount for each of a plurality of focus detection areas of an object field, and determining whether each of the detected plurality of defocus amounts is greater than or equal to a reliability determination threshold value. or it determines, the reliability determination extracts a plurality of defocus amount judgment threshold or more and, on the basis of a plurality of defocus amounts obtained by the extraction determining the final defocus amount, the last defocus the determined the photographic lens is driven on the basis of the amount, the detection, the determination, the extract, a focusing method to run repeatedly a series of focus adjustment operation by the determination and the drive, in the first focusing operation, Detecting a plurality of first defocus amounts corresponding to the plurality of focus detection areas, determining whether the plurality of first defocus amounts is equal to or greater than a first reliability determination threshold; Extracting a plurality of first defocus amounts determined to be equal to or higher than the reliability determination threshold value, determining a first final defocus amount from the extracted first defocus amounts, Corresponding to the plurality of focus detection areas in the second focus adjustment operation subsequent to driving the photographing lens based on the first final defocus amount, driving the photographing lens based on the first final defocus amount. A plurality of second defocus amounts to be detected, and whether or not the plurality of second defocus amounts are equal to or higher than a second reliability determination threshold value higher than the first reliability determination threshold value. Determining, extracting a plurality of second defocus amounts determined to be greater than or equal to the second reliability determination threshold value, and dividing the extracted second defocus amounts into a plurality of groups Process A final group is selected from the group, a second final defocus amount is determined using a defocus amount of the selected final group, and the photographing lens is based on the second final defocus amount. It is characterized by driving .

  According to the present invention, the photographing lens can be accurately focused on the subject intended by the photographer.

  An embodiment in which the focus adjustment apparatus of the present invention is applied to a single-lens reflex camera will be described. The present invention is not limited to a single-lens reflex camera. FIG. 1 is a cross-sectional view of a camera according to an embodiment. The light from the subject that has passed through the photographing lens 1 passes through the half mirror portion of the main mirror 2, is reflected by the sub mirror 3, and is guided to the focus detection device 4. The light from the subject that has passed through the photographing lens 1 is reflected by the main mirror 2 and guided to the finder 5 at the top of the camera. The main mirror 2 and the sub mirror 3 are placed in the photographing optical path as shown before photographing, and are flipped upward and retracted from the photographing optical path during photographing. The control device 6 includes a microcomputer (not shown) and peripheral components such as a memory, and drives and controls the lens driving device 7 based on the focus detection result of the focus detection device 4 to adjust the focus of the photographing lens 1.

  As shown in FIG. 2, the focus detection device 4 has eleven focus detection areas in the photographing screen. Each focus detection area includes a focus detection optical system as shown in FIG. In FIG. 3, the light beam incident through the region 101 of the photographing lens 1 passes through the field mask 200, the field lens 300, the aperture opening 401, and the re-imaging lens 501 and forms an image on the A column of the image sensor array 600. To do. The A column of the image sensor array 600 is a one-dimensional array of a plurality of photoelectric conversion pixels that generate an output corresponding to the incident intensity. Similarly, the light beam incident through the region 102 of the photographing lens 1 passes through the field mask 200, the field lens 300, the aperture opening 402, and the re-imaging lens 502, and forms an image on the B row of the image sensor array 600. To do. The B column of the image sensor array 600 is a one-dimensional array of a plurality of photoelectric conversion pixels that generate an output corresponding to the incident intensity.

  A pair of subject images formed on the A and B columns of the image sensor array 600 are separated from each other in a so-called front pin state in which the photographing lens 1 forms a sharp image of the subject before the planned focal plane, and conversely planned. In the so-called rear pin state in which the sharp image of the subject is connected after the focal plane, the subject images are close to each other. It becomes an interval. Accordingly, the pair of subject images are photoelectrically converted into electric signals by the A and B columns of the image sensor array 600 and converted into electric signals, and these signals are arithmetically processed to obtain the relative positional deviation amounts of the pair of subject images. The focus adjustment state of the lens 100, here, the distance away from the in-focus state and its direction (hereinafter referred to as defocus amount) can be known.

Here, focus detection calculation for calculating the defocus amount will be described. Each of the A column and the B column of the image sensor array 600 includes a plurality of photoelectric conversion pixels, and a plurality of output signal columns a [1],. . . , A [n], b [1],. . . b [n] is output (FIGS. 4A and 4B). Then, the correlation calculation is performed while the data in a predetermined range of the pair of output signal sequences is relatively shifted by L by predetermined data. If the maximum shift number is lmax, the range of L is from −1max to + 1max. Specifically, the correlation amount C [L] is calculated by the following equation.
C [L] = Σ | a [i + L] −b [i] | (1)
In the equation (1), Σ represents the sum of i = k to r, and the first term k and the last term r are changed depending on the shift amount L as in the following equation, for example. L is an integer corresponding to the shift amount of the data string described above, and L = −lmax,. . . , -2, -1, 0, 1, 2,. . . , Lmax.
When L ≧ 0;
k = k0 + INT {−L / 2},
r = r0 + INT {−L / 2},
When L <0;
k = k0 + INT {(− L + 1) / 2},
r = r0 + INT {(−L + 1) / 2} (2)
Here, k0 and r0 are the first term and the last term when the shift amount L is zero.

  Since the relative positional deviation amount is the shift amount L when the pair of data coincides, the shift amount giving the minimum correlation amount is detected from the correlation amount C [L] thus obtained. 3 is multiplied by a constant determined by the pitch width of the photoelectric conversion pixels of the image sensor array 600 and the optical system shown in FIG. Therefore, a larger defocus amount can be detected as the maximum shift number lmax is larger.

Incidentally, the correlation amount C [L] is a discrete value as shown in FIG. 4C, and the minimum unit of defocus amount that can be detected is the photoelectric conversion pixels of the A column and B column of the image sensor array 600. It is limited by the pitch width. Therefore, a method of performing a precise focus detection by newly calculating a true minimum value Cex by performing an interpolation operation based on the discrete correlation amount C [L] will be described. As shown in FIG. 5, this method uses a correlation amount C [Le], which is a minimum value, and correlation amounts C [Le + 1], C [Le-1] in the shift amounts on both sides of the correlation value C [Le-1]. The value Cex and the shift amount Ls that gives it are calculated by the following equation.
DL = (C [Le-1] -C [Le + 1]) / 2
Cex = C [Le]-| DL |,
E = MAX {C [Le + 1] -C [Le], C [Le-1] -C [Le]},
Ls = Le + DL / E (3)
In the formula (3), MAX {Ca, Cb} means that the larger one of Ca and Cb is selected. The defocus amount DF is calculated from the shift amount Ls by the following equation.
DF = Kf · Ls (4)
In the equation (4), Kf is a constant determined by the pitch width of the photoelectric conversion pixels of the optical system and the image sensor array 600 shown in FIG.

It is necessary to determine whether the defocus amount obtained in this way truly indicates the defocus amount or due to fluctuations in the correlation amount due to noise or the like. When the condition shown in the following equation is satisfied, the defocus amount Is trusted.
E> E1 (5),
Cex / E <G1 (6)
In equations (5) and (6), E1 and G1 are reliability determination threshold values. The numerical value E indicates how the correlation amount changes, and is a value that depends on the contrast of the subject. The larger the value, the higher the contrast and the higher the reliability. Cex is a difference when a pair of data most closely matches and is originally 0. However, due to the influence of noise and further, parallax is generated between the area 101 and the area 102, a subtle difference occurs between the pair of subject images and does not become zero. Since the effect of the difference between the noise and the subject image is smaller as the subject contrast is higher, Cex / E is used as a numerical value representing the degree of coincidence between a pair of data. Of course, the closer Cex / E is to 0, the higher the degree of matching between a pair of data and the higher the reliability.

  In this embodiment, the numbers of 11 focus detection areas shown in FIG. 2 are i = 1 to 11, and the defocus amount obtained in these focus detection areas is Def (i). Further, the reliability of each defocus amount is a value E (i) depending on the contrast of the subject shown in the above equation (5), or a numerical value Cex / E ( i).

  As described above, since the defocus amount with high reliability cannot be obtained if the contrast of the subject image in the focus detection area is low, the focus detection area with low defocus amount reliability cannot be included in the grouping process. Like that. However, if the photographing lens 1 is largely out of focus, the contrast of the subject image in the focus detection area is low even if the contrast of the subject itself is high, and the focus detection area is excluded from the group. A grouping process that combines multiple defocus amounts that can be considered into one group cannot be performed correctly.

Therefore, in this embodiment, focus detection and focus adjustment based on the focus detection result are performed twice before and after. In the first focus detection, since there is a high probability that the focus of the photographic lens 1 is greatly shifted, a plurality of first defocus amounts Def1 (i) obtained from eleven focus detection areas i (= 1 to 11). ), A focus detection area having a defocus amount in which reliability E (i) or Cex / E (i) satisfies the following equation is extracted.
E> E11 (7),
Cex / E <G11 (8)
In equations (7) and (8), E11 and G11 are reliability determination threshold values at the first focus detection.

  In the first focus detection, the first final defocus amount Sdef1 is determined using the defocus amount extracted as reliable by the equation (7) or (8). Various methods can be considered for this determination. First, there is a determination method of selecting the closest defocus amount from among a plurality of defocus amounts extracted as reliable as the final defocus amount Sdef1. In general shooting scenes, the closest subject is often the main subject, so it is determined that the main subject intended by the photographer is captured in the focus detection area that detects the closest defocus amount. can do. Alternatively, a simple average or statistical average of a plurality of defocus amounts extracted as reliable may be obtained and used as the final defocus amount Sdef1.

  When the first final defocus amount Sdef1 is determined, the first focus adjustment of the photographing lens 1 is performed based on the final defocus amount Sdef1. After the first focus adjustment, the second focus detection is performed, and the second defocus amount Def2 (i) is detected from 11 focus detection areas i (= 1 to 11). At least in the second focus detection, the taking lens 1 is in focus more than in the first focus detection, so the second defocus amount Def2 (i) is larger than the first defocus amount Def1 (i). Small value.

Next, the reliability E (i) or Cex / E (i) is calculated from the second defocus amount Def2 (i) obtained from the 11 focus detection areas i (= 1 to 11) as follows: A focus detection area having a defocus amount satisfying the above condition is extracted.
E> E12 (9),
Cex / E <G12 (10)
In formulas (9) and (10), E12 and G12 are reliability determination threshold values at the second focus detection.

Here, a value that is more easily determined to be more reliable than the second reliability determination threshold is set as the first reliability determination threshold.
E12> E11 (11),
G12 <G11 (12)
That is, a value smaller than the second threshold value E12, that is, a value that is easily determined to be reliable, is set as the first threshold value E11 of reliability E. Alternatively, the first threshold value G11 of the reliability Cex / E is set to a value larger than the second threshold value G12, that is, a value that is easily determined to be reliable.

  This is a focus detection area in which the main subject is captured in the first focus detection because the photographing lens 1 is more out of focus in the first focus detection than in the second focus detection. Regardless, it is to avoid misidentifying the area as unreliable due to the out-of-focus of the photographic lens 1.

  Next, the reliability E (i) or Cex / E (i) is (9) from the second defocus amount Def2 (i) obtained from the eleven focus detection areas i (= 1 to 11). ) Or (10) is satisfied, and the final defocus amount Sdef2 for the second time is determined using the defocus amount extracted as reliable. Various methods can be considered for this determination. First, there is a determination method of selecting the closest defocus amount from among a plurality of defocus amounts extracted as reliable as the final defocus amount Sdef2. As described above, in general shooting scenes, the closest person or the like is often the main subject, so the subject intended by the photographer is captured in the focus detection area that detects the closest defocus amount. Can be determined.

  Further, the grouping process is performed as described above using the plurality of defocus amounts Def2 (i) extracted as reliable in the second focus detection, and the second final defocus amount Sdef2 is determined. Good. That is, a plurality of defocus amounts Def2 (i) are grouped into defocus amount groups that can be regarded as capturing the same subject, and the best match with the photographer's intention among the plurality of defocus amount groups. A possible defocus amount group is selected, and statistical averaging is performed in the selected defocus amount group to determine the second final defocus amount Sdef2.

  As is clear from the equations (11) and (12), each defocus is performed using the reliability determination threshold value E12 or G12 that is less likely to be determined to be reliable in the second focus detection than in the first focus detection. Since the amount reliability determination is performed, a defocus amount with higher reliability than the defocus amount obtained in the first focus detection can be obtained in the second focus detection. Since the final defocus amount Sdef2 is determined using such a reliable defocus amount, as compared with the case where the grouping process is performed immediately based on the first focus detection result as in the conventional focus adjustment device. Thus, a more reliable final defocus amount Sdef2 can be obtained.

  Further, by performing focus adjustment of the taking lens 1 based on such a highly reliable second final defocus amount Sdef2, the subject in the focus detection area that captures the main subject intended by the photographer is accurately detected. The photographing lens 1 can be brought into focus.

  FIG. 6 is a flowchart showing the focus adjustment operation of the embodiment. The controller 6 starts this focus adjustment operation when the camera is turned on. In step 1, it is confirmed whether or not a shutter button (not shown) is half-pressed. If the shutter button is half-pressed, the process proceeds to step 2. In step 2, the first focus detection is performed to detect the defocus amount Def1 (i) of eleven ranging areas i (= 1 to 11). In the subsequent step 3, the defocus amount in which the reliability E (i) or Cex / E (i) satisfies (7) and (8) is extracted from the first defocus amount Def1 (i) and extracted. As described above, the first final defocus amount Sdef1 is determined using the defocus amount. In step 4, the focus of the photographic lens 1 is adjusted according to the first final defocus amount Sdef1.

  In step 5 after the first focus adjustment, the second focus detection is performed to detect the defocus amount Def2 (i) of eleven ranging areas i (= 1 to 11). In the subsequent step 6, the defocus amount that satisfies the reliability E (i) or Cex / E (i) (9) and (10) is extracted from the second defocus amount Def2 (i) and extracted. As described above, the final defocus amount Sdef2 for the second time is determined using the defocus amount. In step 7, the focus of the photographic lens 1 is adjusted according to the second final defocus amount Sdef2.

  As described above, according to the embodiment, the photographing lens can be accurately focused on the subject intended by the photographer.

The figure which shows the structure of one embodiment Layout of focus detection area on the shooting screen Diagram showing focus detection optical system Diagram explaining the reliability of focus detection results Diagram explaining the reliability of focus detection results The flowchart which shows the focus adjustment operation | movement of one Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting lens 4 Focus detection apparatus 6 Control apparatus 7 Lens drive device

Claims (3)

Detection means for detecting a defocus amount for each of a plurality of focus detection areas of the object field;
Determination means for determining whether each of a plurality of defocus amounts detected by the detection means is greater than or equal to a reliability determination threshold;
Extraction means for extracting a plurality of defocus amounts determined by the determination means to be equal to or higher than the reliability determination threshold ;
Determining means for determining a final defocus amount based on a plurality of defocus amounts extracted by the extracting means ;
Driving means for driving the taking lens based on the final defocus amount determined by the determining means ;
Said detecting means, said determining means, said extracting means, and a repeat that perform control means a series of focus adjustment operation by the determining means and the drive means,
In the first focus adjustment operation,
The detecting means detects a plurality of first defocus amounts corresponding to the plurality of focus detection areas;
The determination unit determines whether or not the plurality of first defocus amounts are equal to or greater than a first reliability determination threshold value;
The extraction means extracts a plurality of first defocus amounts determined by the determination means to be equal to or higher than the first reliability determination threshold value,
The determining unit determines a first final defocus amount from the plurality of first defocus amounts extracted by the extracting unit;
The driving means drives the photographing lens based on the first final defocus amount,
In the second focus adjustment operation following the driving of the photographing lens based on the first final defocus amount,
The detecting means detects a plurality of second defocus amounts corresponding to the plurality of focus detection areas;
The determination means determines whether the plurality of second defocus amounts are equal to or higher than a second reliability determination threshold value higher than the first reliability determination threshold value;
The extraction means extracts a plurality of second defocus amounts determined by the determination means to be equal to or greater than the second reliability determination threshold;
The determining unit performs a grouping process for dividing the plurality of second defocus amounts extracted by the extracting unit into a plurality of groups, selects a final group from the plurality of groups, and selects the selected final A second final defocus amount is determined using a typical group defocus amount,
The focus adjustment apparatus , wherein the driving unit drives the photographing lens based on the second final defocus amount . The focus adjustment apparatus according to claim 1,
In the first focus adjustment operation, the determination unit preferentially uses the nearest defocus amount among the plurality of first defocus amounts extracted by the extraction unit, and uses it by the driving unit. A focus adjustment device that determines a first final defocus amount . A defocus amount is detected for each of a plurality of focus detection areas of the object scene, and it is determined whether each of the detected defocus amounts is equal to or greater than a reliability determination threshold, and the reliability determination threshold is determined. Extracting a plurality of defocus amounts determined to be equal to or greater than a value, determining a final defocus amount based on the plurality of extracted defocus amounts , driving a photographing lens based on the determined final defocus amount , detecting, the determining, the extraction, a focusing way to repeatedly perform a series of focus adjustment operation by the determination and the drive,
In the first focus adjustment operation,
Detecting a plurality of first defocus amounts corresponding to the plurality of focus detection areas;
Determining whether the plurality of first defocus amounts are equal to or greater than a first reliability determination threshold;
Extracting a plurality of first defocus amounts determined to be equal to or greater than the first reliability determination threshold;
Determining a first final defocus amount from the extracted first defocus amounts;
Driving the taking lens based on the first final defocus amount;
In the second focus adjustment operation following the driving of the photographing lens based on the first final defocus amount,
Detecting a plurality of second defocus amounts corresponding to the plurality of focus detection areas;
Determining whether or not the plurality of second defocus amounts are equal to or higher than a second reliability determination threshold value higher than the first reliability determination threshold value;
Extracting a plurality of second defocus amounts determined to be equal to or greater than the second reliability determination threshold;
A grouping process for dividing the extracted second defocus amounts into a plurality of groups, selecting a final group from the plurality of groups, and determining a defocus amount of the selected final group To determine the second final defocus amount,
The focus adjustment method, wherein the photographing lens is driven based on the second final defocus amount .

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