JP2002182106A - Focusing control system for digital still video camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an appropriate focusing control based on a focal evaluated value in a block within a specified focus position range from which a low contrast block and a block having a high luminance part are removed in the focal evaluated values in a plurality of blocks at respective focus positions. SOLUTION: This control system is equipped with a block forming means for dividing one part or all of an image plane to a plurality of blocks, a state detection means for obtaining whether a luminance level obtained from the specified block obtained by the block forming means is within the range of the luminance level being a certain reference, a focal evaluated value generating means for generating the focal evaluated value in a plurality of blocks from a video signal, and a peak candidate group forming means for obtaining a new synthetic focal evaluated value further based on the focal evaluated value within the range of the specified focus position in the focal evaluated values in a plurality of blocks at the respective focus positions. Then, the focusing control is performed based on results by the focal evaluated value generating means and the peak candidate group forming means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focusing control method using a focus evaluation value by a plurality of blocks in automatic focus adjustment of a digital still video camera using an individual imaging device represented by a CCD imaging device. Furthermore, the present invention relates to a focusing control method applicable to a video camera.

[0002]

2. Description of the Related Art Conventionally, in a video camera, several types of automatic focusing devices (autofocus) have been proposed and implemented. Among them, a so-called "hill-climbing system" is known as a system utilizing a video signal from a CCD image pickup device (NHK Technical Research Showa 40 Vol. 17, No. 1, page 21 "Mounting of a TV camera using a mountain-climbing servo system"). Focus adjustment ”, Ishida et al.).

This is a method utilizing the fact that the level of a frequency component (high frequency component) of a video signal which is equal to or higher than a certain value corresponds to the degree of contrast of a subject. When the high-frequency component of the video signal is detected as a focus evaluation value for each field, the focus evaluation value increases as the degree of contrast increases, and a peak (peak) occurs at the in-focus position.
Becomes

[0004] The "hill climbing method" utilizes this property,
The focus adjustment is performed by always comparing the focus evaluation value with the one before one field, and moving and controlling the lens position so that the focus evaluation value becomes maximum.

[0005]

With the above-described hill-climbing method, it is possible to perform good focus adjustment control on a subject having a normal contrast. But,
If the subject to be focused mainly has no contrast or low contrast at the center of the screen, the focus evaluation value contains many noise components and an accurate focus evaluation value cannot be obtained. There was a problem that the focusing failed and accurate focusing control could not be performed.

Further, the above-mentioned hill-climbing method can perform good focus adjustment control on an object having a normal contrast without including a local high-luminance portion such as a light source on the screen.

However, when there is a saturated high luminance portion such as a light source, a high frequency component is generated at an edge portion due to the saturation. Therefore, when the screen includes a local high-luminance portion such as a light source, the degree of contrast of the high-luminance portion becomes clearer as the image is blurred, so that the focus evaluation value increases and a pseudo peak is generated. I will. For this reason, this pseudo peak position is set as the focus position,
There is a problem that the focus adjustment control fails.

The present invention has been made in order to solve such a problem. In the focus evaluation values of a plurality of blocks at each focus position, a block having a low contrast and a block having a high luminance portion have been removed. It is an object of the present invention to provide a system capable of performing appropriate focusing control by performing control based on a focus evaluation value in a block within a predetermined focus position range.

[0009]

The above object of the present invention is achieved by the following means. According to claim 1 of the present invention, in a digital still video camera that converts the luminance of a subject into an electric signal using a solid-state imaging device and records or records and reproduces image information in the form of an electric signal,
Block generating means for dividing a part or the whole of the screen into a plurality of blocks; and determining whether a luminance level obtained from the predetermined block obtained by the block generating means is within a reference luminance level range. State detection means, focus evaluation value generation means for generating a focus evaluation value in a plurality of blocks from a video signal, and a focus within a predetermined focus position range in the focus evaluation values of a plurality of blocks at each focus position Based on the evaluation value,
A peak candidate group generating means for newly obtaining an overall focus evaluation value, wherein focusing control is performed based on the results of the focus evaluation value generating means and the peak candidate group generating means.

According to a second aspect of the present invention, in the focusing control method for a digital still video camera according to the first aspect, the peak candidate group generation means includes a focus position from infinity to a close side, The cumulative luminance of each block is equal to or less than a predetermined threshold, and the maximum value of the focus evaluation value at the focus position from infinity to the closest side is equal to or more than the predetermined threshold, and A block in which the ratio of the minimum value to the maximum value of the focus evaluation value at the focus position is equal to or less than a predetermined threshold is used.

According to a third aspect of the present invention, in the focusing control method of the digital still video camera according to the first aspect, the peak candidate group generation means includes a focus position from infinity to a close side. Among the cumulative luminances of the blocks in the predetermined area at the center of the screen, those having a value greater than a predetermined threshold value occupy a predetermined ratio or more, do not newly calculate the overall focus evaluation value, It is characterized in that a predetermined position determined in advance is a focus position.

According to a fourth aspect of the present invention, in the focus control method for a digital still video camera according to the first aspect, the peak candidate group generating means includes a focus at a focus position from infinity to a close side. The block in which the maximum value of the evaluation value is smaller than a predetermined threshold value, or the ratio of the minimum value to the maximum value of the focus evaluation value at the focus position from infinity to the closest side is larger than the predetermined threshold value, When the area occupies a predetermined ratio or more within a predetermined area in the center of the screen, a new predetermined focus position is not obtained, and a predetermined position is set as a focus position.

According to a fifth aspect of the present invention, in the focusing control method of the digital still video camera according to the first aspect, the peak candidate group generating means includes a predetermined area in a central area of the screen. A new overall focus evaluation value is generated using a focus evaluation value within a predetermined range near the focus position where the focus evaluation value is maximized in the block, and a focus position is determined based on the new total focus evaluation value. It is characterized by doing.

According to a sixth aspect of the present invention, in the focusing control method for a digital still video camera according to the fifth aspect, the peak candidate group generating means includes a predetermined area in a central area of the screen. When the transition of the focus evaluation value at a specific focus position at the focus position within a predetermined range near the focus position at which the focus evaluation value becomes the maximum for all the blocks occupies a predetermined ratio or more. The specific focus position is set as the focus position.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of the present invention will be described based on embodiments. First, the basic configuration of the present invention is shown in FIG.
11 is a lens, 12 is an aperture, 13 is a CCD which is a charge-coupled device, 14 is a CDS which is a double correlation sampling circuit for reducing noise of accumulated charge of the image sensor, and 15 is an AGC circuit which automatically adjusts a gain of an image signal. , 16 is an A / D conversion circuit, 17 is an image signal processing circuit for mixing an A / D converted image signal into a luminance signal and a chrominance signal conforming to the NTSC system and converting it into a divided video signal, and 18 is a screen image. A block generation circuit that divides a part or the whole into a plurality of blocks and accumulates the luminance signal output from the image signal processing circuit 17 in each block to obtain the accumulated luminance. A state detection circuit for determining whether or not the luminance level is within a reference luminance level range; a band-pass filter (B) for extracting only a frequency component of a certain band; F) and 21 are focus evaluation value generation circuits that generate focus evaluation values in a plurality of blocks based on frequency components extracted from the BPF 20, and 22 calculates an exposure amount based on the output of the state detection circuit 19. The exposure control circuit 23 controls the aperture, shutter speed, and AGC. The focus evaluation value in a plurality of blocks at each focus position is determined based on the focus evaluation values in blocks within a predetermined focus position range. Further, a peak candidate group generation circuit for generating a focus evaluation value and obtaining a so-called in-focus position, which is a position where the subject is in focus, is provided with a focus evaluation value generation circuit 21, a peak candidate group generation circuit 23, Is a focus control circuit that determines a final focus position based on the output of the lens, and 25 is a focus drive circuit that drives the lens.

Hereinafter, 8 × 6 from the block generation circuit 18 will be described.
The operation of the present invention will be described by taking as an example the case where the accumulated luminance of a block is generated. Here, suppose that the name of each block is B (i,
j) (i = 1 to 8, j = 1 to 6). FIG. 2 shows the state of division of the screen. 8 when the focus position is at infinity
The cumulative luminance of × 6 blocks is represented by Y1 (i, j) (i = 1 to 8, j = 1
To 6). Area 1 in FIG. 2 is used as an example below as a range for generating the focus evaluation value of each block and for generating the accumulated luminance.

FIG. 3 shows an example of the processing flow of the state detection circuit 19. In the initial state, it is assumed that it is not within the range of the reference luminance level.

The determination as to whether the luminance is within the range of the reference luminance level corresponds to Yl_thrd <Yc <Yu_thrd. As Yc, for example, an average value of all blocks in area 1 in FIG. 2 is used. That is, Yc = ΣY1 (i, j) / 16
(I = 3 to 6, j = 2 to 5) Yl_thrd and Yu_thrd are lower and upper thresholds that determine the range of the reference luminance level.

CV is a reference value T which is a reference luminance level.
The correction amount is calculated as follows, for example. CV = -log2 (T / Yc) When implementing, the CV may be obtained by linear interpolation or the like.

PEV and qEV are arbitrary EVs (Exposure Vacuum) that can cover the entire photometric range during photometry.
lue). In a general scene, the subject of each luminance included in the screen has a range of about 5 EV. Therefore, for example, when the photometric range is 9 to 17 EV, the entire area can be covered by setting p = 13 and q = 16. When it is determined that the brightness is within the range of the reference luminance level, the focus control is performed by the peak candidate group generation circuit 23, the focus control circuit 24, and the focus drive circuit 25.

The BPF 20 extracts a high frequency component in a certain band from the luminance signal converted by the image signal processing circuit 17.

The focus evaluation value generation circuit 21 uses the focus drive circuit 25 to, for example,
While driving the lens, the high frequency component from the BPF 20 is
The focus evaluation value is generated by accumulating in each block in the area 1 in FIG.

The exposure control circuit 22 obtains an exposure amount (EV) corresponding to the brightness of the subject based on the entire area 1 based on the CV in the state detection circuit 19, and controls the aperture, shutter speed, and AGC 15. Do.

Hereinafter, an embodiment until the focus position is determined will be described.
The peak candidate group generation circuit 23 will be described.

After the state of the reference luminance level is reached by the processing of the state detection circuit 19 and the exposure control circuit 22, the lens is driven over the entire range from the infinity side to the close side of the focus area, and n
It is assumed that individual focus evaluation values have been obtained at the focus position of the point. At the n-point focus position, FIG.
Assuming the name of the block in area 1 of C (j) (j = 1 to 16)
And the focus evaluation value of each obtained block is A (j) Sk
(j = 1 to 16, k = 1 to n).

FIG. 4 shows the names of the individual blocks in the area 1 and their focus evaluation values. In each block, the upper part shows the name, and the lower part shows the focus evaluation value.

FIG. 5 shows an example of a focus position for acquiring a focus evaluation value of n points and a transition of the focus evaluation value. In FIG. 5, the vertical axis is the focus evaluation value level, the horizontal axis is the focus position, the left direction is the infinity side, and the right direction is the close side. Hereinafter, in the drawings showing the focus positions, the focus positions are described in the same direction.

The accumulated luminance of 8 × 6 blocks at the n-point focus position from the infinity side to the close side is Yk (j) (j = 1 to 16, k = 1 to n).

The peak candidate group generation circuit 23 first performs a high-luminance block determination process. Hereinafter, the high luminance block determination processing will be described.

Block C (j) in area 1 in FIG. 4 (j = 1
In 1616), a block whose accumulated luminance may become larger than a predetermined value y_thrd during a change in focus is defined as a high luminance block. That is, C (j) satisfying max (Yk (j), (k = 1 to n))> y_thrd is called a high luminance block. The total number of blocks satisfying this condition is the number of high-luminance blocks y_num, and the total number of blocks in area 1 in FIG. 4 is b_all (b_al in FIG. 1).
l = 16).

FIG. 6 shows an example of luminance level change in an arbitrary block at the n-point focus position. FIG.
The vertical axis indicates the luminance level and the horizontal axis indicates the focus position.
In the figure, A is an example in which the entire block has high brightness. In the figure, B is an example in which the high-brightness part is located at infinity and the high-brightness part is included in a part of the block, and since the blur amount increases toward the close side, it occupies the block. This is an example in which a high-luminance portion increases, a luminance level increases, and a high-luminance block is formed. In the figure, C is an example in which no high-luminance part exists in the block.

The total number of blocks b_all in area 1 in FIG.
, The number of high-brightness blocks y_num is a predetermined ratio y
If it occupies more than _rate (%), a high-brightness exception flag is set, the process of peak candidate group generation ends, and the flow advances to the focus control circuit 24. Otherwise, the process proceeds to the low contrast determination process. That is, if (y_num × 100) / b_all ≧ y_rate Set a high-brightness exception flag Go to the focus control circuit 24 else Go to the low contrast determination process

After that, the focus evaluation value corresponding to the high luminance block is not used. At the position in area 1 in FIG. 4, the number of blocks remaining after removing high-luminance blocks is represented by b
_All2.

Next, the low contrast determination processing will be described. Hereinafter, the focus evaluation values A (1) S1 to A (1) Sn at the n-th focus position of the block C (1) will be described as an example.

Of A (1) S1 to A (1) Sn, the largest one is a1_
Let max be the smallest and a1_min be the smallest. a1_max is greater than or equal to a predetermined threshold value af_evl_thrd, and the ratio of a1_min to a1_max is a predetermined threshold value af_rate_thr
If d or less, the block of C (1) in area 1 is a block with contrast, otherwise it is a block without contrast. That is,

If ((a1_max ≧ af_evl_thrd) && (a1
_Min × 100) / a1_max ≤ af _rate_thrd)) Block with contrast else Block without contrast

This determination is made based on the focus evaluation value A of another block.
(j) Sk (j = 2 to 16, k = 1 to n) is also performed. Let the total number of blocks without contrast be n_cnst_num. Here, the number of blocks without contrast n_cnst_
num is a predetermined ratio const_ra to the number of remaining blocks b_all2 from which high-luminance blocks in area 1 have been removed.
If it occupies te_thrd or more, a low contrast exception flag is set, the process of peak candidate group generation ends, and the flow advances to the focus control circuit 24. Otherwise, the process proceeds to the maximum value group generation process. That is,

If (n_cnst_num × 100) / b_all2 ≧ co
nst_rate_thrd Set low-contrast exception flag. Go to focus control circuit 24. else Go to peak candidate group generation processing.

Thereafter, the focus evaluation value of the low contrast block is not used. In area 1 of FIG.
The number of blocks remaining after removing low-contrast blocks is set to b_all3.

Next, the peak candidate group generation processing will be described. FIG. 7 shows the flow of the peak candidate group generation processing.
Shown in First, of the remaining blocks at this point, n
Focus evaluation value A (i) Sk at point focus position
A histogram relating to the focus position at which (k = 1 to n) is maximized is obtained (processing in step S1).

FIG. 8 shows a block C (2) having the maximum value A (2) Sk-1 at the focus position k-1 and a block having the maximum value A (1) Sk at the focus position k at the n-point focus position. Focusing evaluation of C (1), block C (3) with maximum value A (3) Sk + 1 at focus position k + 1, and block C (10) with maximum value A (10) Sn at focus position n An example in which the value changes is shown.
In FIG. 8, the vertical axis represents the focus evaluation value level, and the horizontal axis represents the focus position.

FIG. 9 shows an example of a histogram of the focus position at which A (i) Sk is maximized. FIG. 9 is an example, and has no relation to FIG. In FIG. 9, the vertical axis represents the frequency of the focus evaluation value at each focus position which is the maximum, and the horizontal axis represents the focus position.

Next, the total of the frequencies on the long-distance side and the short-distance side, that is, the number of distributions is calculated (processing in step S2). In FIG. 9, bd_thrd is a predetermined focus position that divides the long distance side and the short distance side. The total number of distributions on the far side is b_al
l3_f, the total number of distributions on the short distance side is b_all3_n (the total number of distributions at this point is b_all3), and the position at which the frequency becomes maximal on the short distance side in the long distance side is m
ax_ptr_f.

FIG. 10 shows an example in which a predetermined focus position for dividing the long distance side and the short distance side is changed. In FIG. 10, the vertical axis indicates the frequency of the focus evaluation value at each focus position which is the largest, and the horizontal axis indicates the focus position.

Based on max_ptr_f, a predetermined focus range in the short distance direction is dist_thrd_n, and a predetermined focus range in the long distance direction is dist_thrd_f. Here, when max_ptr_f + dist_thrd_n ≧ bd_thrd, the predetermined focus position bd_thrd for dividing the long distance side and the short distance side is changed to max_ptr_f + dist_thrd_n (new bd_thrd in FIG. 10), and again. And the number of distributions on each side. In this case, the long-distance side is a position from the infinity-side focus position to max_ptr_f + dist_thrd_n ("new long-distance side" in FIG. 10), and the total number of distributions is b.
_All3_f '. On the short distance side, max_ptr_f + dist
_Thrd_n + 1 to the nearest position (in FIG. 10, "
New short distance side "), and the total number of distributions is b_all3_n '. M
When ax_ptr_f + dist_thrd_n ≧ bd_thrd, b_all3_f ′ = b_all3_fb_all3_n ′ = b_all3_n, and the boundary bd_thrd on the long distance side and the short distance side is not changed. Terms in the figures other than those described here will be described later.

Next, a peak candidate group is generated (step S3). In generating the peak candidate group, it is first determined whether the focus evaluation value on the long distance side or the short distance side is to be used. Distribution number on the far side b_al
l3_f 'is a predetermined ratio far_r to the total number of distributions b_all3
If it occupies ate_thrd or more, the focus evaluation value corresponding to the distribution on the long distance side is used; otherwise, the focus evaluation value corresponding to the distribution on the short distance side is used. That is,

If (b_all3_f '× 100) / b_all3 ≧ far
_Rate_thrd Use distribution on long distance else Use distribution on short distance

The far_rate_thrd determines which distance side to use, but far_rate_thrd is a value that gives priority to the short distance side when the distribution numbers on the short distance side and the long distance side are almost the same. Set to.

In each of the determined distributions on the distance side, the position at which the frequency becomes maximum on the shorter distance side is max_ptr, and the frequency of the position is hmax_num. In FIG. 9 described above, max_ptr = max_ptr_ is an example using a distribution on the long distance side.
f. Also, the total distribution on the determined distance side is cand_
Let it be num. That is, cand_num = b_all3_f 'when the determined distance side is a long distance side distribution, and cand_num = b_all3_n' when the determined distance side is a short distance side distribution.

Based on max_ptr, a set of blocks distributed at a focus position within a predetermined focus range dist_thrd_n in the short distance direction and a predetermined focus range dist_thrd_f in the long distance direction is defined as a peak candidate group. . That is, from max_ptr-dist_thrd_f
A group of blocks having a maximum focus evaluation value at a focus position up to max_ptr + dist_thrd_n is defined as a peak candidate group.

The number of blocks included in the peak candidate group is represented by rep_num, and the blocks of the peak candidate group are assumed to be D (j).
(J = 1 to rep_num), and the focus evaluation value of each block is
R (j) Sk '(j = 1 to rep_num). Note that k 'is ma
x_ptr-dist_thrd_f to max_ptr + dist_thrd_
Within n, the focus position is the focus position where the focus evaluation value of the block D (j) (j = 1 to rep_num) is the maximum.

FIG. 11 shows an example of R (j) Sk '. For example,
The pointillism portion corresponding to the subject is R (j) Sk '. In the figure, Sk 'is omitted.

After the peak candidate group is determined, the in-focus position is obtained based on the determined group. It is determined whether the frequency hmax_num at the focus position of max_ptr is larger than a predetermined ratio h_rate with respect to the number of blocks rep_num of the peak candidate group (processing in step S4), and the predetermined ratio h
When the value is larger than _rate, the position of max_ptr is set as the focus position (the process of step S5). Otherwise, the process proceeds to the process of step S6.

In the case of proceeding to step S5, in the case of max_pt
Since the distribution is almost concentrated near r, subjects with contrast at the same distance occupy on the screen,
It is assumed that a focus evaluation value without error is generated.

In step S6, the ratio of the number of blocks rep_num of the peak candidate group in the determined total distribution cand_num on the distance side is determined, and the step S7 or the step Decide which process of S8 is to be performed.

The number of blocks of the peak candidate group rep_nu
If m is greater than a predetermined ratio d_rate with respect to each determined total distribution cand_num on the distance side, step S7
Then, the in-focus position is obtained using R (j) Sk 'and the like. If not, the process proceeds to step S8, and the in-focus position is obtained using the central block in FIG. 4, for example, C (6), C (7), C (10), and C (11).

In the case of proceeding to step S7, max_pt
Since the distribution is relatively concentrated near r, it is assumed that a focus evaluation value is generated in a state where a relatively high-contrast subject occupies the screen.

In the case of proceeding to step S8, since the distribution is scattered, it is assumed that the focus evaluation value is generated somewhat instable because the screen contains some subjects without contrast. Therefore, in this case, the central area is prioritized, and the focus evaluation value there is used.

Next, step S7 will be described. Focus position is max_ptr-dist_thrd_f to max_ptr
Within the range of ptr + dist_thrd_n, R (j) Sk 'and A (i) Sk' at the same focus position are added to newly obtain a total focus evaluation value. That is, max_ptr-dist_thrd_f
And max_ptr + dist_thrd_n, R (j) S
Assuming that the acquisition point of the focus evaluation value of k 'is q points, the total focus evaluation value is P1, P2, ..., Pq in order from the position of max_ptr-dist_thrd_f to the closest direction, and
The block in the screen corresponding to R (j) Sk 'is D (l) (l = 1
Rep_num) and the corresponding focus evaluation value as A ′ (l) Sk ′, the total focus evaluation value Pm (m = 1 to q) becomes Pm = ΣA ′ (l) S
k '(l = 1 to rep_num). Note that the focus position k ′ is represented by max_ptr−dist_thrd_f to max_ptr +
The focus position where R (j) Sk ′ in dist_thrd_n exists, that is, the focus position for point m.

FIG. 12 shows an example in the case of (q = 3, rep_num = 6). In FIG. 12, the vertical axis represents the focus evaluation value level, and the horizontal axis represents the focus position, which is an example corresponding to R (j) Sk ′ in FIG. Note that the description of the focus position Sk 'is omitted in the figure.

Taking FIG. 12 as an example, Pm is obtained by integrating the focus evaluation values of the marks ● and □ at the same focus position.

Using FIGS. 11 and 12 as examples, R (j) Sk ′ and A ′ (l)
The correlation of Sk 'is specifically shown. If the description of the focus position Sk 'is omitted, it is as follows. A '(1) = R (1) = A (6), A' (2) = R (2) = A (7) A '(3) = R (3) = A (10), A' ( 4) = R (4) = A (11) A '(5) = R (5) = A (14), A' (6) = R (6) = A (15) It looks like this: D (1) = C (1) = B (6), D (2) = C (2) = B (7) D (3) = C (3) = B (10), D (4) = C (4) = B (11) D (5) = C (5) = B (14), D (6) = C (6) = B (15)

In this Pm, the focus position where the maximum value is obtained on the shorter distance side is defined as the focus position.

Step S8 will be described. In step S8, the central block, for example, B (6), B (7), B (1
Using (0) and B (11), the overall focus evaluation value is obtained in the same manner as in step S7, and the in-focus position is obtained based on the evaluation value. However,
The focus range is on the distance side (step S3).
The overall focus evaluation value is calculated within the range of the short distance side or the long distance side. Assuming that the focus position on the distance side determined in step S3 is r point, from the long distance direction in the range on the distance side where the total focus evaluation value is determined,
Expressed in order as P'1, P'2, ..., P'r, the overall focus evaluation value
P'm is P'm = A (6) Sk "+ A (7) Sk" + A (10) Sk "+ A (11) Sk" (m =
1 to r) Here, k "is a focus position corresponding to the point m. When the distance side determined in step S3 is the long distance side,
k "= 1 to bd_thrd When the distance side determined in step S3 is the short distance side,
k "= bd_thrd + 1 to n. In this P'm, the focus position where the maximum value is obtained on the shorter distance side is set as the focus position.

FIG. 13 shows an example in which the distance side determined in step S3 is the long distance side. In FIG. 13, the vertical axis represents the focus evaluation value level, and the horizontal axis represents the focus position. FIG.
Taking 3 as an example, P'm is the
It is obtained by integrating the focus evaluation values indicated by □.

The focus control circuit 24 determines the final focus position based on the result from the peak candidate group generation circuit 23. FIG. 14 shows the processing flow. When the high-brightness exception flag or the low-contrast exception flag is set, a predetermined position such as infinity is set as the focus position (the processing of step S10 or step S11). The predetermined position may be separately set for each of the high-brightness exception flag and the low-contrast exception flag. If the high-brightness exception flag and the low-contrast exception flag do not stand together, the step S7 or the step S7
The in-focus position obtained in step 8 is set as the final in-focus position (step S12).

The focus drive circuit 25 moves to the focus position finally determined by the focus control circuit 24, and the focus control ends.

FIGS. 15 to 18 show specific examples of various scenes in the area 1 and FIGS. 19 to 22, respectively.
18 shows an example of a histogram at a focus position where the focus evaluation value of the block in area 1 corresponding to FIGS. In FIGS. 19 to 22, the vertical axis represents the frequency of the focus evaluation value at each focus position which is the maximum, and the horizontal axis represents the focus position. 15 to FIG.
It is just one example for explanation,
This is not always the case.

FIG. 15 shows an example in which a single contrasted subject (hatched portion) occupies the screen, the subject is located on the near side, and the background is located on the far side.

FIG. 19 shows an example in which a single contrasted subject is occupied on the screen, so that the distribution is concentrated near a certain in-focus position of the subject. In the peak candidate group generation processing, step S5 or , Step S
It is assumed that the processing of FIG.

FIG. 16 shows a situation in which a long-distance object and a short-distance object are mixed, and the short-distance object is located at a distance.
This is an example where the center is open (hollowed out).
The subject in the hatched portion is located on the near side, and the subject in the stippled portion is located on the far side.

FIG. 20 shows an example in which distributions are concentrated on the short distance side and the long distance side because the objects on the long distance side and the objects on the short distance side are mixed. It is assumed that the short-distance side is prioritized by the processing in step S2, and the processing in step S5 or step S7 will respond. Through the peak candidate group generation processing, it is also possible to prevent a dropout.

FIG. 17 shows an example in which a high-luminance part is included in the upper part.
Both the subject and the high-luminance part in the hatched portion are located on the far distance side. In FIG. 21, the distribution of the stippled portion means that of the high-luminance portion (since the degree of contrast of the high-luminance portion becomes clearer toward the short distance side, and the focus evaluation value increases). When the position is obtained, the block corresponding to the distribution of the stippled portion is deleted, and the block corresponding to the distribution of the hatched portion is used. In the peak candidate group generation process, step S5 or step S5 is performed.
It is assumed that the processing of FIG.

FIG. 18 shows an example in which a portion having no contrast is included in the upper portion, and a portion having little or no contrast is occupied as a whole, and a portion having some contrast is located in the center portion. Where there is no contrast,
The stippled portion is a portion with a slightly low contrast, and the hatched portion is a portion with a little contrast, all of which are located on the far side.

In FIG. 22, the distribution is scattered because the low contrast part is occupied as a whole.
A portion without contrast (distribution of a plain portion in the graph) is large and represents a dispersed state. When obtaining the in-focus position, the block corresponding to the distribution of the solid portion is deleted, and the block corresponding to the distribution of the oblique lines and the stippling portion (other than the portion having no contrast) is used. , The processing in step S8 is assumed. In this case, it is assumed that the value of the focus evaluation value is somewhat unstable due to the distribution being dispersed (or when subjects are scattered at various distances), and the area in the center is prioritized. In some cases, or in some cases, a low-contrast exception process (step S11 in FIG. 14) is performed to increase the focusing accuracy.

As a result, it is possible to perform highly accurate focusing control by responding to various scenes by the peak candidate group generation processing.

[0077]

As described above, the following effects can be obtained by the focusing control method of the present invention.

According to the focus control method of the digital still video camera according to the first aspect, it is possible to perform appropriate focus control for various scenes.

Further, according to the focus control method of the digital still video camera of the second aspect, since an unstable focus evaluation value including an error is not used, it is possible to perform accurate focus control. .

According to the focus control method of the digital still video camera of the third aspect, since control using an unstable focus evaluation value including an error is not performed, it is possible to maintain the focus accuracy. Become.

According to the focus control method of the digital still video camera of the fourth aspect, since control using an unstable focus evaluation value including an error is not performed, it is possible to maintain the focus accuracy. Become.

According to the focus control method for a digital still video camera of the present invention, a focus evaluation value having a high accuracy near the focus position is used, and the focus accuracy can be improved. .

Further, according to the focus control method of the digital still video camera of the sixth aspect, it is possible to save the trouble of newly generating the total focus evaluation value, and to focus on the focus concentrated near the focus position. Since the focus position is determined based on the evaluation value, it is possible to perform accurate and appropriate focus control.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a basic configuration of the present invention.

FIG. 2 is a diagram showing a state of division of a screen.

FIG. 3 is a diagram illustrating an example of a processing flow of a state detection circuit 19.

FIG. 4 is a diagram showing names of individual blocks in an area 1 and their focus evaluation values.

FIG. 5 is a diagram illustrating an example of a focus position for acquiring an n-point focus evaluation value and a transition of the focus evaluation value.

FIG. 6 is a diagram illustrating an example of a luminance level change in an arbitrary block at an n-point focus position.

FIG. 7 is a diagram showing a flow of a peak candidate group generation process.

FIG. 8 is a diagram illustrating an example of transition of each focus evaluation value at an n-point focus position in some blocks.

FIG. 9 is a diagram illustrating an example of a histogram of a focus position at which A (i) Sk is maximized.

FIG. 10 is a diagram illustrating an example in which a predetermined focus position for dividing a long distance side and a short distance side is changed.

FIG. 11 is a diagram illustrating an example of R (j) Sk ′.

FIG. 12: Overall focus evaluation value Pm (m = 1 to q) = Σ
It is a figure which shows the example in the case of A '(l) Sk' (l = 1-rep_num) (q = 3, rep_num = 6).

FIG. 13 is a diagram illustrating an example in which the distance side is a long distance side.

FIG. 14 is a diagram showing a flow of the focus control circuit 24.

FIG. 15 is a specific example 1 of various scenes in the area 1;
FIG.

16 is a specific example 2 of various scenes in the area 1. FIG.
FIG.

FIG. 17 is a specific example 3 of various scenes in the area 1;
FIG.

FIG. 18 is a specific example 4 of various scenes in the area 1;
FIG.

FIG. 19 is a diagram illustrating an example of a histogram at a focus position where a focus evaluation value of a block in an area 1 corresponding to a specific example 1 of a scene is maximum.

FIG. 20 is a diagram illustrating an example of a histogram at a focus position where a focus evaluation value of a block in an area 1 corresponding to a specific example 2 of a scene is maximum.

FIG. 21 is a diagram illustrating an example of a histogram at a focus position where a focus evaluation value of a block in an area 1 corresponding to a specific example 3 of a scene is maximum.

FIG. 22 is a diagram illustrating an example of a histogram at a focus position where a focus evaluation value of a block in an area 1 corresponding to a specific example 4 of a scene is maximum.

[Explanation of symbols]

 Reference Signs List 17 image signal processing circuit 18 block generation circuit 19 state detection circuit 20 BPF 21 focus evaluation value generation circuit 22 exposure control circuit 23 peak candidate group generation circuit 24 focus control circuit

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Claims (6)

[Claims] 1. A digital still video camera that uses a solid-state imaging device to convert the brightness of a subject into an electric signal and records or records and reproduces image information in the form of an electric signal. Block generating means for dividing the image into blocks; state detecting means for determining whether a luminance level obtained from the predetermined block obtained by the block generating means is within a range of a reference luminance level; In a plurality of blocks, focus evaluation value generation means for generating a focus evaluation value, and in each focus position, in the focus evaluation value of a plurality of blocks,
Based on the focus evaluation value within a predetermined focus position range, further comprising a peak candidate group generation unit for newly obtaining an overall focus evaluation value, wherein the focus evaluation value generation unit and the peak candidate group generation unit A focus control method for a digital still video camera, wherein focus control is performed based on a result. 2. A focusing control method for a digital still video camera according to claim 1, wherein said peak candidate group generating means sets a cumulative brightness of each block to a predetermined value at a focus position from infinity to a close side. The maximum value of the focus evaluation value at the focus position from the infinity to the close side which is equal to or less than the threshold value and the maximum value of the focus evaluation value at the focus position from the infinity to the close side is equal to or more than the predetermined threshold value. A focus control method for a digital still video camera, wherein a block whose ratio of the minimum value is equal to or less than a predetermined threshold value is used. 3. The focusing control method for a digital still video camera according to claim 1, wherein said peak candidate group generating means is a focus position from infinity to a close side and is located within a predetermined area in a central portion of the screen. If the cumulative luminance of a block that is higher than a predetermined threshold occupies a predetermined ratio or more, a new overall focus evaluation value is not obtained, and the predetermined position is set to the in-focus position. A focus control method for a digital still video camera. 4. A focusing control method for a digital still video camera according to claim 1, wherein said peak candidate group generating means determines that a maximum value of a focus evaluation value at a focus position from infinity to a close side is a predetermined threshold. Less than the value,
Alternatively, a block in which the ratio of the minimum value to the maximum value of the focus evaluation value at the focus position from infinity to the closest side is larger than a predetermined threshold value is within a predetermined area in the center of the screen, and If it occupies more than
A focus control method for a digital still video camera, characterized in that a new predetermined focus value is not obtained and a predetermined position is set as a focus position. 5. The focus control method for a digital still video camera according to claim 1, wherein the peak candidate group generation unit focuses on a block having a maximum focus evaluation value in a block in a predetermined area at the center of the screen. A digital still video camera characterized in that a new total focus evaluation value is generated using a focus evaluation value at a focus position within a predetermined range near a position, and a focus position is determined based on the new total focus evaluation value. Focus control method. 6. A focusing control method for a digital still video camera according to claim 5, wherein said peak candidate group generating means has a maximum focus evaluation value for all blocks in a predetermined area at the center of the screen. When a block in which the transition of the focus evaluation value is maximum at a specific focus position at a focus position within a predetermined range near the focus position becomes a predetermined ratio or more, the specific focus position is set to the in-focus position. A focus control method for a digital still video camera.