JP2018105948A - Focus detection method, and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method that synthesizes signals of lines having similarity for improving focus detection accuracy to enhance a contrast, and enables detection of focusing on a desired part.SOLUTION: A focus detection method according to the present invention, which is a phase difference method focus detection method, has a sensor that has a plurality of lines detecting images for calculating a phase difference between two images. When similarity is present between the line in a correlation direction of attention for implementing a correlation computation and the line orthogonal to the line in the correlation direction thereof, the focus detection method calculating an amount of defocus on the basis of a signal having both lines synthesized by synthesis means, has: multiple line determination means that determines a plurality of lines to be used for implementing the correlation computation; and reference line determination means that determines a line serving as a benchmark for reviewing the similarity from the multiple line determination means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a focus detection method used for automatic focus detection, and more particularly to a signal generation method used during detection.

  Conventionally, a phase difference detection method is known as one of automatic focus detection methods. In the phase difference detection method, each image formed by two light fluxes having different exit pupils is read by a line sensor, a correlation operation is performed using the read signal, a phase difference amount (distance) between the two images is calculated, and a defocus amount is obtained. The focus is detected by converting to. In order to improve the focus detection accuracy, a method of synthesizing signals used for calculation is known. The aim is to improve the correlation calculation accuracy by combining and thereby improve the accuracy of the correlation calculation, and thus the accuracy of the defocus amount.

  For example, in Patent Document 1, the similarity between the signal of the line to be correlated and the signal of the line adjacent to the direction orthogonal to the direction is investigated. To calculate defocus. When there is no similarity, a defocus is calculated by performing a correlation operation on each signal sequence. This is applied to all lines, and if all are finally similar, the weighted average from the viewpoint of reliability is used as the final defocus amount. If there is even one signal pair with no similarity, the closest defocus is the final defocus.

JP 2006-145862 A

  However, if there is even one line pair with no similarity, the preceding example is configured to focus on the closest defocus point from among the multiple defocus amounts calculated without combining the signals. ing. Recently, the pixel size has been reduced to improve the resolution, so the number of lines for investigating similarity is increasing compared to conventional sensors. As the number of lines increases, the probability that there is a line pair having no similarity among all the lines increases, and the probability that the defocus amount calculated without combining the signals becomes the final defocus amount increases.

  As a result, it is impossible to achieve the purpose of improving the focusing accuracy by synthesizing the signals to generate a signal with high contrast. In addition, since the closest defocus point is selected, it may not be possible to focus on a desired location.

  The present invention has been made in view of the above problems, and an object of the present invention is to improve contrast by synthesizing signals of similar lines in order to improve focus detection accuracy, and to detect focus at a desired location. .

In order to achieve the above object, the focus detection method of the present invention comprises:
This is a phase difference type focus detection method, which has a sensor having a plurality of lines for detecting images in order to calculate the phase difference between two images, and has a correlation direction of interest for performing correlation calculation. To perform correlation calculation in a focus detection method that calculates a defocus amount based on a signal obtained by synthesizing both lines by a synthesizing unit when there is a similarity between the line and a line in a direction orthogonal thereto. And a plurality of line determination means for determining a plurality of lines to be used for the first and second reference line determination means for determining a reference line for investigating similarity among the plurality of line determination means.

  According to the present invention, the accuracy of focus detection can be increased.

1 is a block diagram showing a configuration of a camera according to a first embodiment of the present invention. The figure which shows the optical component of the camera in 1st Embodiment, and its example of arrangement | positioning Diagram showing focus detection sensor and its logical division Figure with ranging points superimposed on the viewfinder Correspondence between focus detection sensor and focus point displayed on viewfinder Flowchart of the first embodiment Image formed with focus detection sensor Diagram showing similarity to the reference line Diagram showing dissimilarity with the reference line Lines judged to be similar in the focus detection sensor Reference line signal before synthesis and signal after synthesis Relationship between distance measurement frame and focus detection sensor area

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, shapes, relative arrangements, and the like of the components exemplified in the description should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions, and the present invention is limited to these examples. Is not to be done.

[Example 1]
(Camera operation outline)
FIG. 1 is a block diagram illustrating a configuration of a camera as an example of an optical apparatus using a focus detection sensor according to an embodiment of the present invention. Since the configuration of the camera is widely known, the configuration related to auto focus detection deeply related to the present invention is mainly shown. The switch 103 has two switches SW1 and SW2 that are turned on and off by operating a release button (not shown). The switch SW1 is turned on by the first stroke (half press) operation of the release button, and the switch SW2 is turned on by the second stroke (full press) operation of the release button. In general, preparation for shooting is performed by turning on the switch SW1, and shooting is performed by turning on the switch SW2.

  The focusing operation will be described. When the switch SW1 is turned on, a focusing operation is performed. Focus detection is performed on a desired distance measuring point, and the focus lens in the photographing lens is controlled through the lens communication circuit 104 to perform focusing. The camera CPU 100 communicates with a photographing lens (not shown) through the lens communication circuit 104 to control the aperture and focus lens. Further, the shutter mechanism is controlled through the shutter control circuit 107 to open and close the shutter.

  The distance measuring point selection switch 108 selects an arbitrary distance measuring point from among a plurality of distance measuring points (focus detection areas) arranged in the shooting screen by operating a selection button (not shown). The positional relationship between the shooting screen and the distance measuring point will be described later. The camera CPU 100 includes a subject determination unit 102, determines the main subject position from the information of the distance measuring point selection switch 108, and performs focus using the focus detection sensor 101.

  When SW2 is turned on, the camera CPU 100 controls the photometric sensor 106 to detect the brightness of the subject, and determines the imaging conditions such as the aperture value of the photographing lens and the shutter speed according to the subject brightness. Then, the shutter is opened by the shutter control circuit, and the image sensor 105 is exposed. The camera CPU 100 reads out the electric charges accumulated by the image sensor 105 and applies known image processing to generate photographed image data and record it on a recording medium (not shown).

(Camera optical parts placement)
FIG. 2 is a cross-sectional view showing the optical components of the camera and an arrangement example thereof in the present embodiment. The light beam from the subject incident through the imaging lens 200 is reflected upward by the quick return mirror 201 constituting the half mirror, and forms an image on the finder screen 202. The photographer observes the subject image formed on the finder screen 202 through the pentarhythm 203 and the eyepiece lens 204. The viewfinder screen 202 is configured by superimposing a transmissive liquid crystal on a focus plate that captures a subject image, and displays various types of information related to shooting on the shooting screen. This includes a distance measuring point selected by operating the distance measuring point selection switch 108.

  A photometric imaging lens 211 and a photometric sensor 106 are disposed above the eyepiece lens 204. The photometric sensor 106 can measure the subject luminance by receiving the subject image formed on the finder screen 202 through the photometric imaging lens 211. The combination and arrangement of the photometric imaging lens 211 and the photometric sensor 106 in FIG. 2 are examples, and the configuration and arrangement are not limited to those in FIG. 2 as long as the subject luminance can be measured.

  Of the light flux incident from the imaging lens 200, the light flux that has passed through the quick return mirror 201 is guided to the focus optical system by the rear submirror 205. The light beam incident on the focus detection optical system forms an image on the focus detection sensor 101 through the field mask 206, the infrared cut filter 207, the field lens 208, the stop 209, and the secondary imaging lens 210. The focus state (defocus amount) of the imaging lens 200 can be detected based on the phase difference of image signals obtained by photoelectrically converting the formed image with the focus detection sensor 101.

  When the switch SW2 is turned on and photographing is performed, the quick return mirror 201 and the sub mirror 205 change the position to open the optical path, and the shutter opens to cause the imaging sensor 105 to move at the speed of light of the subject image incident from the imaging lens 200. Exposed.

(Positional relationship between line sensor layout and ranging points)
Taking the case where a two-dimensional area sensor is used as the focus detection sensor 101 as an example, the configuration and use method will be described with reference to FIG. When a line sensor is used as the focus detection sensor, the position of the line arranged on the sensor can be determined in accordance with the image to be formed. On the other hand, in the two-dimensional area sensor, since the pixel position of the sensor unit is determined from the beginning, that is, the position of the line is determined, it is necessary to match the pixel position to be detected with the image to be formed. For this purpose, the area is logically divided. Specifically, in order to detect and measure two pairs of light beams output from the focus detection optical system, the areas are also divided into pairs.

  The image formed on the focus detection sensor moves in a direction with the base line length of the secondary imaging lens 210 as an axis in accordance with the defocus amount with the subject. For this reason, the paired images are arranged at positions sharing the axis. FIG. 3 shows a sensor that detects an image moving in the left-right direction 304 using 302A and 302B. The defocus amount of the imaging lens can be detected from the shift amount (phase difference) in the baseline length direction of the signal images obtained from 302A and 302B.

(Correspondence between the image on the sensor surface and the image seen from the viewfinder)
Light from the subject passes through the taking lens 200 and is separated by the main mirror 201 into the viewfinder side and the focus detection side. Since the field of view of the light separated to the focus detection side is limited by the field mask, a part of the image on the finder side is seen. However, since the image seen on the focus detection side has a corresponding relationship with the image seen on the finder side, a distance measurement frame on which the user can select a focus is shown on the finder, and a corresponding location is set on the sensor surface.

  FIG. 4 is an image in which an in-focus portion called a distance measuring frame is superimposed on an image seen from the viewfinder, and FIG. 5 is a diagram showing how the distance measuring point corresponds to the focus detection sensor. . As described above, the focus detection sensors 502A and 502B are paired, and each of them has a portion corresponding to a distance measuring frame that can be seen from the finder. When the user selects a range-finding frame, correlation calculation is performed using a signal output from the location of the sensor corresponding to the range-finding frame to obtain a defocus amount. For convenience of explanation, the size relationship between each distance measurement frame shown in the figure and the pixels of the focus detection sensor is not considered. Actually, many pixels correspond to each ranging point.

(Main topic)
The cause of the problem to be solved by the invention is that the similarity of the signals output by the sensors in the target region is investigated, and if it is determined that there is no similarity, the signal synthesis of the line is not performed. The defocus amount is calculated individually, and the closest end is selected from them.

  Therefore, in this proposal, a reference line is determined, and whether other lines have similarity to the reference line is investigated. As a result, if there is similarity, the data is synthesized, and if there is no similarity, the method of not synthesizing is adopted. By doing so, even if there is no similarity as a whole, data can be combined if there is similarity in part, and defocus accuracy can be improved. Further, since the reference is set, the in-focus position can be focused at a desired position without being pulled by the result of other lines.

The implementation method will be described in detail with reference to the flowchart of FIG.
(S101) In order to detect the focus, it is determined which data of the focus detection sensor is to be used. For example, if a range-finding frame is designated, the data of the focus detection sensor corresponding to it is used. FIG. 7 shows an area used for focus detection in a part of the focus detection sensor 300 shown in FIG. A fine square represents a pixel of the sensor, and a hatched square in the square represents a region where an image formed is detected. In addition, the numbers on the left in the figure are numbers assigned to refer to the horizontal lines in the following.

  (S102) A reference line is determined from the data determined in S101. If a distance measurement frame is designated, a reference line may be determined at the center of the distance measurement frame, or a line having the highest contrast between lines may be determined. In FIG. 7, the center line (line 6) is determined as the reference line in the region determined in S101.

  (S103, S104) The similarity between the reference line and a line other than the reference line selected in S101 is investigated. As described in Patent Document 1, the similarity investigation method can be determined from the correlation amount obtained by adding the absolute value of the difference between the reference line signal and the investigation target signal for each pixel. If the signal of the reference line and the signal to be investigated match, the correlation amount becomes zero, but the correlation amount increases as the coincidence decreases. Using this feature, if the correlation amount is smaller than the determination value, it is determined that there is a similarity.

FIG. 8 shows the reference line 6 and the line 5 adjacent thereto. Since the line 5 and the line 6 are detected at the same location where the image is formed, it is determined that there is similarity. FIG. 9 is a diagram in which run 6 and line 4 which are reference lines are extracted. The line 6 and the line 4 are determined not to be similar because the positions where the formed images are detected are shifted.
(S105) If it is determined that there is similarity in S104, a flag of “similarity” is set on the line for which the similarity was investigated.

  (S106) The similarity with the reference line 6 is investigated for all lines (lines 6 excluding lines 1 to 11). FIG. 10 is a diagram in which hatched lines that are determined to be similar to the reference line after all line surveys are performed. The line 5 and the line 7 were determined to be similar to the reference line 6. These are groups of lines that are determined to be able to improve the defocus amount calculation accuracy when combined. Since the lines 1 to 4 and the lines 8 to 11 have little or no similarity to the reference line 6, they are combined with the reference line. Is a line group determined to be unable to improve the defocus amount calculation accuracy.

  (S107) When the similarity to the reference line is investigated for all lines, the data of the line flagged as similar and the data of the reference line are synthesized. As means for combining, there are addition, arithmetic average, weighted average, etc., but the method is determined while comparing the accuracy of the defocus amount. FIG. 11 shows the reference line data and the combined data. When similar data is synthesized, it can be seen that the signal is smooth and the contrast of the portion where the image data is output is improved.

  (S108) The correlation calculation is performed using the data synthesized in S107, and the defocus amount is calculated. For example, a known method can be used to calculate the defocus amount. Comparing the case where the defocus amount is obtained with the reference line alone and the case where the defocus amount is obtained by synthesizing a line similar to the reference line, it is possible to find unnecessary fluctuation components by performing the operation of combining the lines. As a result, the original signal appears. Further, since the operation of selecting a line having similarity is performed, the original shape of the signal is not destroyed. It is considered that the accuracy of the defocus amount is improved in combination with these things.

  The phase difference detection method requires information of two images. The above describes the flow for one of the images. The plurality of lines, reference lines, and lines to be combined determined in the above flow are applied to the other image in a dependent manner.

[Modification 1]
When it is determined that the investigation target line is similar to the reference line, the reference line may be updated by synthesizing the signal each time. Since the noise component of the reference line signal is reduced by combining, in the subsequent similarity determination, it is determined that the similarity is higher than the original signal, and the signal can be combined.

[Modification 2]
Depending on the configuration of the apparatus, the distance measurement frame may not match the area of the plurality of lines selected in S101, and the distance measurement frame 3201 may be included in the area 300 of the plurality of lines as shown in FIG. Although the line outside the distance measurement frame may be handled in the same way as other lines, the main signal is the signal that should not be used because it is within the distance measurement frame. However, on the other hand, if the contrast is improved by synthesizing signals outside the distance measurement frame and the defocus accuracy is improved, it is also a signal to be synthesized. In such a case, it is preferable to change the similarity determination threshold value between the lines within the distance measurement frame and the lines outside the frame. Although the similarity determination threshold value change is described above and outside the distance measurement frame, the similarity determination threshold value may be changed according to the distance from the reference line even within the distance measurement frame.

DESCRIPTION OF SYMBOLS 101 Focus detection sensor 200 Imaging lens 201 Quick return mirror 205 Sub mirror 206 Field mask 207 Infrared cut filter 208 Field lens 209 Aperture 210 Secondary imaging lens 300 Focus detection sensor 302A, 302B Focus detection sensor logical division 502A, 502B Focus detection Correspondence between sensors and ranging points

Claims (4)

In order to calculate the phase difference between the two images, the sensor has a plurality of lines for detecting the images,
If there is a similarity between the line in the correlation direction of interest for performing the correlation calculation and the line in the direction orthogonal thereto, the defocus amount is based on the signal obtained by combining the two lines by the combining means. In the focus detection device for calculating
A plurality of line determining means for determining a plurality of lines to be used for performing the correlation calculation;
A focus detection apparatus comprising reference line determination means for determining a reference line for investigating similarity among the plurality of line determination means. The reference line determining means includes
Select the line located at the center of multiple lines,
Or select a line with high contrast among multiple lines,
The focus detection apparatus according to claim 1. The reference line determining means includes
3. The focus detection apparatus according to claim 1, wherein a signal generated by combining the reference line and one of a plurality of lines by the combining unit is used as a new reference line signal. It is a focus detection apparatus of any one of Claims 1 thru | or 3,
A distance measuring point specifying means for specifying a focus position (ranging point) or a focus area (ranging frame);
A plurality of line determining means for selecting a plurality of lines corresponding to the distance measuring points or the distance measuring frames specified by the distance measuring point specifying means;
The focus detection apparatus according to claim 1, wherein the focus detection apparatus is a focus detection apparatus.