JP2009069740A - Image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image pickup device, wherein the focusing accuracy on the entire pickup image screen is improved. <P>SOLUTION: The image pickup device includes: an extracting means 110 that extracts a signal indicating the high frequency component of a subject from a signal obtained from the light receiving face of an image pickup means 103 corresponding to a plurality of photometry areas on the image pickup screen; a peak position detecting means 111 that detects the contrast peak positions of the plurality of photometry areas relative to the signal extracted by the extracting means; a peak position information storage means 112 that stores the contrast peak position information for each of the photometry areas in advance; and a focusing position correction amount calculating means 113 that calculates the amount of focusing position correction based on the difference between the photometry area of the detected central part and the contrast peak position of the photometry area of a peripheral part and the difference between the photometry area of the central part stored in advance and the contrast peak position of the photometry area of the peripheral part, and then outputs the amount of focusing position correction to a focus lens drive control means 114, thereby controlling the drive of the focus lens. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus such as a digital camera or a video camera having an automatic focusing function.

2. Description of the Related Art Conventionally, digital cameras, video cameras, and the like have been provided with an automatic focus detection device that performs high-frequency components of luminance signals obtained from an image sensor such as a CCD and performs a focusing operation. In this automatic focus detection apparatus, the lens position with the highest contrast is detected by integrating the high frequency component of the signal within the ranging area (autofocus area) arbitrarily or automatically set in the imaging screen, The in-focus position is generally obtained (Patent Document 1, etc.).
JP 2002-122773 A

  However, the conventional example has the following problems. Due to differences in design values such as field curvature due to image height of the imaging optical system and manufacturing errors, the optimal focus position differs between the center and periphery of the imaging screen, and the focus position is set at the center of the imaging screen. When the adjustment is made, the peripheral portion of the imaging screen deviates from the optimum focus position. For this reason, a difference in resolution occurs between the central portion and the peripheral portion of the imaging screen, and a sense of incongruity occurs in the captured image.

(Object of invention)
An object of the present invention is to provide an imaging apparatus capable of improving the focusing accuracy over the entire imaging screen.

  To achieve the above object, focus lens drive control means for controlling the drive of the focus lens, imaging means for receiving a subject image formed by the focus lens and converting it into an electrical signal, and a plurality of images on the imaging screen An extraction means for extracting a signal indicating a high-frequency component of a subject from a signal obtained from the light receiving surface of the imaging means corresponding to the distance measurement area, and the plurality of distance measurement areas for the signal extracted by the extraction means A peak position detecting means for detecting a contrast peak position, a peak position information storing means for storing contrast peak position information in each of the plurality of distance measuring areas in advance, and a distance measuring area and a peripheral part of the detected central part The difference between the contrast peak positions of the distance measurement area and the contrast peak of the center distance measurement area and the peripheral distance measurement area stored in advance. A focus position correction amount calculating unit that calculates a focus position correction amount based on a difference in position and outputs the focus position correction amount to the focus lens drive control unit to control driving of the focus lens; The imaging device is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which can improve the focusing precision in the whole imaging screen can be provided.

  The best mode for carrying out the present invention is as shown in the following examples.

  FIG. 1 is a block diagram showing an imaging apparatus according to an embodiment of the present invention. The imaging apparatus includes an imaging lens 101 that captures an image, a focus lens 102 for focus adjustment included in the imaging lens 101, and an imaging element 103 that photoelectrically converts a subject image formed by the imaging lens 101. Furthermore, an A / D converter 104 that converts an analog signal from the image sensor 103 into a digital signal, an electronic finder 105 that displays an image converted into a digital signal by the A / D converter 104, and a digitized image Is temporarily stored. Furthermore, the image processing unit 107 that performs image processing such as white balance, the image recording unit 108 that records the finally formed image, and the detection unit 109 that detects the zoom position and aperture value state of the imaging lens 101 are provided. .

  Here, the signal from the A / D converter 104 is input to an extraction unit 110 that extracts signals indicating high-frequency components in a plurality of ranging areas corresponding to the light receiving surface of the image sensor 103. The high frequency component signals for the plurality of ranging areas extracted by the extraction unit 110 are input to the peak position detection unit 111 that detects the peak position of the high frequency component with respect to the extracted signals. A peak position storage unit 112 that stores in advance peak positions of high-frequency components (hereinafter referred to as contrast peak positions) in a plurality of distance measurement areas on the screen corresponding to each zoom position of the imaging lens 101 and subject distance for each aperture value. The contrast peak position is stored. The contrast peak position information stored in the peak position storage unit 112 is a design value of the imaging lens 101 or an actually measured value at the time of assembly.

  Based on the detection information in the peak position detection unit 111 corresponding to the distance measurement area, the detection information in the detection unit 109 that detects the zoom position and the aperture value, and the contrast peak position information stored in advance in the peak position storage unit 112 The focus position correction amount calculation unit 113 calculates the focus position correction amount. Based on the focus position correction amount output from the focus position correction amount calculation unit 113, the focus lens drive control unit 114 drives the focus lens 102 to optimize the focus position with respect to the subject.

  Next, the procedure for performing the focus position correction will be described with reference to the flowchart of FIG.

  When a switch SW1 (not shown) provided in the imaging apparatus is turned on, the focus lens drive control unit 114 drives the focus lens 102 in step # 201. Then, the peak position detection unit 111 detects the contrast peak positions in a plurality of distance measurement areas (specifically, the light receiving surfaces of the image sensor 103 corresponding to the plurality of distance measurement areas) set in the imaging screen. The focus lens 102 is scanned all over the screen, and the signal processing for calculating the contrast peak position is performed for a plurality of distance measuring areas. A plurality of ranging areas are automatically set in the imaging apparatus, or are picked up by the ranging area near the center of the imaging screen for photographing a main subject arbitrarily set by the photographer. This is a distance measurement area set in advance in the periphery of the screen.

  In the next steps # 202, # 203, and # 204, the contrast peak position at the center of the screen is compared with the contrast peak position at the periphery of the screen. The comparison of the contrast peak positions is performed as follows. The contrast peak position with respect to the same focus lens position differs between the screen center of the imaging screen (near the center of the light receiving surface of the image sensor 103) and the periphery of the screen due to field curvature and manufacturing errors of the imaging lens 101. The contrast peak position at the time of design or actual measurement is stored in advance in the peak position storage unit 112, and the stored contrast peak position and the contrast peak position detected in each distance measurement area obtained when the focus lens 102 is driven. Compare As a result of the comparison, the process of step # 206, # 207, # 208 or step # 205 is executed. Details of these operations will be described below.

  First, in step # 202, the contrast peak position stored in the peak position storage unit 112 is compared with the contrast peak position detected in each ranging area obtained when the focus lens 102 is driven.

  The above comparison and the results will be described with reference to FIG. The difference between the contrast peak position A at the center of the screen stored in the peak position storage unit 112 and the contrast peak position B at the periphery of the screen is the reference value a, and the contrast peak at the center of the screen obtained when the focus lens 102 is driven. It is assumed that the difference x between the position A and the contrast peak position B at the periphery of the screen is also the reference value a. In this case, the focus position correction amount calculation unit 113 determines that the subject distance is the same at the screen center and the screen periphery, and proceeds from step # 202 to step # 206. In step # 206, since the subject distance is the same at the screen center and the screen periphery, the focus lens 102 is driven to a predetermined focus adjustment position C between the contrast peak positions of the screen center and the screen periphery. To do. That is, the focus adjustment position C is calculated as a focus position correction amount, and the focus lens drive control unit 114 is driven to drive the focus lens 102 based on the focus position correction amount. As a result, the shift from the in-focus position at the center of the screen and the periphery of the screen is reduced, the difference in resolution within the screen is reduced, and the focusing accuracy on the entire imaging screen is improved. Thereafter, the process proceeds to step # 209.

  Next, a case where the process proceeds to step # 203 on the assumption that the difference x between the contrast peak position A at the center of the screen and the contrast peak position B at the periphery of the screen obtained when the focus lens 102 is driven is not the reference value a. 4 will be described.

  In step # 203, the contrast peak position stored in the peak position storage unit 112 is compared with the contrast peak position detected in each distance measurement area obtained when the focus lens 102 is driven. Specifically, the difference between the contrast peak position A at the center of the screen stored in the peak position storage unit 112 and the contrast peak position B at the periphery of the screen is the reference value a, and the center of the screen obtained when the focus lens 102 is driven. It is assumed that the difference x between the contrast peak position A and the contrast peak position B at the periphery of the screen is equal to or less than the threshold value b (b ≧ x> a). In this case, the in-focus position correction amount calculation unit 113 determines that the subject distance is different between the central portion of the screen and the peripheral portion of the screen, but is within a certain subject depth, and proceeds from step # 203 to step # 207. . In step # 207, the position of the focus lens 102 is adjusted to the focus adjustment position D on the contrast peak position B side with respect to the predetermined focus adjustment position C in the middle of the contrast peak position between the screen center and the screen periphery. That is, the focus adjustment position D is calculated as an in-focus position correction amount, and the focus lens drive control unit 114 drives the focus lens 102 based on the in-focus position correction amount. As a result, the difference in resolution between the center of the screen and the periphery of the screen is reduced, and the focusing accuracy over the entire imaging screen is improved. Thereafter, the process proceeds to step # 209.

  Next, it is assumed that the difference x between the contrast peak position A at the center of the screen and the contrast peak position B at the periphery of the screen obtained when the focus lens 102 is driven is greater than the threshold value b or less than the reference value a. The advanced case will be described with reference to FIG.

  In step # 204, the contrast peak position at the center of the screen stored in the peak position storage unit 112 is compared with the contrast peak position detected in each ranging area obtained when the focus lens 102 is driven. Specifically, the difference between the contrast peak position A at the center of the screen and the contrast peak position B at the periphery of the screen stored in the peak position storage unit 112 is the reference value a, and the contrast peak position obtained when the focus lens 102 is driven. Assume that the difference x between A and the contrast peak position B at the periphery of the screen is equal to or greater than a threshold c (a> x ≧ c). In this case, the focus position correction amount calculation unit 113 advances the process from step # 203 to step # 208. Then, the position of the focus lens is adjusted to a focus adjustment position E on the contrast peak position A side with respect to a predetermined focus adjustment position C between the contrast peak positions of the screen center and the screen periphery. That is, the focus adjustment position E is calculated as an in-focus position correction amount, and the focus lens drive control unit 114 is caused to drive the focus lens 102 based on the in-focus position correction amount. As a result, the difference in resolution between the center of the screen and the periphery of the screen is reduced, and the focusing accuracy over the entire imaging screen is improved. Thereafter, the process proceeds to step # 209.

  It is assumed that the difference x between the contrast peak position A at the center of the screen and the contrast peak position B at the periphery of the screen is determined to be greater than the threshold b or less than the threshold c in the processes of steps # 203 and # 204. In this case, the subject distance between the center of the screen and the periphery of the screen is sufficiently large, and even if the resolution of the image at the periphery of the screen is inferior to that of the center, the image does not feel strange. Therefore, the focus position correction amount calculation unit 113 determines that it is not necessary to reduce the difference in resolution between the screen center and the screen periphery, and proceeds from step # 204 to step # 205. Here, the position of the focus lens 102 is adjusted to the contrast peak position A in the center of the screen. That is, the contrast peak position A at the center of the screen is calculated as the focus position correction amount, and the focus lens drive control unit 114 is driven based on the focus position correction amount. Thereafter, the process proceeds to step # 209.

  In step # 209, it is determined whether or not a switch SW2 (not shown) provided in the imaging apparatus is turned on. If not, the process returns to step # 201, and the same operation as described above is repeated. Thereafter, when the switch SW2 is turned on, the process proceeds to step # 210 to perform a known photographing operation.

  The adjustment of the position of the focus lens 102 is performed on position information stored in the peak position storage unit 112 corresponding to each zoom position of the imaging lens 102 and subject distance for each aperture value. The threshold values b and c and the focus adjustment positions C, D, and E are also set for each zoom position and each aperture value of the imaging lens 102.

  The image pickup apparatus according to the embodiment includes a focus lens drive control unit 109 that drives the focus lens 102, and an image pickup element 103 that receives a subject image formed by the focus lens 102 and converts it into an electrical signal. Furthermore, an extraction unit 110 that extracts a signal indicating a high-frequency component of a subject from signals obtained on the light receiving surface of the image sensor 103 corresponding to a plurality of distance measurement areas set on the imaging screen arbitrarily or automatically. Have Furthermore, a peak position detection unit 111 that detects the contrast peak positions of a plurality of ranging areas with respect to the signal extracted by the extraction unit 110, and a peak position storage that stores contrast peak position information in each of the plurality of ranging areas in advance. Part 112. Further, the focus position correction amount is calculated by comparing the contrast peak positions of the detected plurality of distance measurement areas with the contrast peak positions of the plurality of distance measurement areas stored in advance. Then, a focus position correction amount calculation unit 113 that outputs the focus position correction amount to the focus lens drive control unit 109 to drive the focus lens 102 is provided.

  Assume that the contrast peak positions stored in advance coincide with the detected contrast peak positions of a plurality of ranging areas. In this case, the in-focus position correction amount calculation unit 113 sets an intermediate position between the contrast peak position near the center of the light receiving surface of the image sensor 103 and the contrast peak position near the periphery as the in-focus position correction amount.

  Further, the focus position correction amount calculation unit 113 has a difference between the contrast peak position near the center of the light receiving surface of the image sensor 103 and the contrast peak position near the periphery outside the set range (threshold values b and c). In some cases, the contrast peak position near the center is used as the focus position correction amount.

  When the imaging lens has a plurality of zoom positions or a plurality of aperture values, the peak position information storage unit 112 stores the contrast peak position information for each of the plurality of zoom positions or the plurality of aperture values. Similarly, when the imaging lens has a plurality of zoom positions or a plurality of aperture values, the focus position correction amount calculating unit 113 calculates a focus position correction amount corresponding to the plurality of zoom positions or the plurality of aperture values.

  As described above, the contrast peak position information is a design value of the imaging lens or an actual measurement value of the imaging lens.

  With the above configuration, in order to perform focus position correction in consideration of field curvature of the imaging optical system of the plurality of ranging areas on the imaging screen and image plane displacement due to image height due to manufacturing errors, the screen A good focus position can be obtained for the whole.

(Correspondence between the present invention and the embodiment)
The focus lens 102 is the focus lens of the present invention, the focus lens drive controller 109 is the focus drive controller, the image sensor 103 is the imager, the extractor 110 is the extractor, and the peak position detector 111 is the peak position detector. Respectively. The peak position storage unit 112 corresponds to the peak position information storage unit of the present invention, and the focus position correction amount calculation unit 113 corresponds to the focus position correction amount calculation unit. Further, within the set range described in claim 2 means within the threshold values b and c shown in FIGS. 4 and 5, and outside the set range described in claim 3 means that in FIG. Means outside the thresholds b and c shown in FIG.

It is a block diagram which shows the imaging device concerning one Example of this invention. It is a flowchart which shows the operation | movement at the time of focus lens position adjustment concerning one Example of this invention. It is a figure for demonstrating the relationship of the difference of the contrast peak position of the screen center part and screen periphery part in step # 206 of FIG. It is a figure for demonstrating the relationship in case the difference of the contrast peak position of the screen center part and screen peripheral part in step # 207 of FIG. 2 is below the threshold value b. The figure for demonstrating the relationship in case the difference of the contrast peak position of the screen center part and screen periphery part in step # 208 of FIG. 2 is more than the threshold value c.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Imaging lens 102 Focus lens 103 Imaging element 109 Detection part 110 Extraction part 111 Peak position detection part 112 Peak position information storage part 113 Focus position correction amount calculation part 114 Focus lens drive control part A, B Contrast peak position C, D, E Focus adjustment position a Reference value b, c Threshold

Claims (7)

Focus lens drive control means for controlling the drive of the focus lens;
Imaging means for receiving a subject image formed by the focus lens and converting it into an electrical signal;
An extraction means for extracting a signal indicating a high-frequency component of a subject from a signal obtained from a light receiving surface of the imaging means corresponding to a plurality of ranging areas on the imaging screen;
Peak position detecting means for detecting contrast peak positions of the plurality of ranging areas with respect to the signal extracted by the extracting means;
Peak position information storage means for storing contrast peak position information in each of the plurality of ranging areas in advance;
Based on the difference between the detected contrast peak positions in the central and peripheral ranging areas, and the difference between the contrast peak positions in the central and peripheral ranging areas stored in advance. And a focus position correction amount calculating means for calculating a focus position correction amount and outputting the focus position correction amount to the focus lens drive control means to control the drive of the focus lens. An imaging device.   The in-focus position correction amount calculating means is configured to determine whether a difference between contrast peak positions of the detected distance measurement area in the central portion and the distance measurement area in the peripheral portion is stored in the central distance measurement region and the peripheral portion. If the difference is within the range set based on the difference in contrast peak position of the distance measurement area, the contrast peak position of the detected distance measurement area in the center and the distance measurement area in the detected peripheral area. The imaging apparatus according to claim 1, wherein an intermediate position of a contrast peak position is set as the focus position correction amount.   The in-focus position correction amount calculating means is configured to determine whether a difference between contrast peak positions of the detected distance measurement area in the central portion and the distance measurement area in the peripheral portion is stored in the central distance measurement region and the peripheral portion. When the contrast peak position of the distance measurement area is outside the range set with reference to the difference in contrast peak position of the distance measurement area, the contrast peak position of the detected distance measurement area in the center is used as the focus position correction amount. The imaging apparatus according to claim 1.   When the imaging lens has a plurality of zoom positions or a plurality of aperture values, the peak position information storage means stores the contrast peak position information for each of the plurality of zoom positions or the plurality of aperture values. The imaging apparatus according to claim 1, wherein the imaging apparatus is characterized in that:   The imaging apparatus according to claim 4, wherein the focus position correction amount calculation unit calculates the focus position correction amount according to the plurality of zoom positions or the plurality of aperture values.   6. The imaging apparatus according to claim 1, wherein the contrast peak position information stored in advance by the peak position information storage means is based on a design value of the imaging lens.   6. The imaging apparatus according to claim 1, wherein the contrast peak position information stored in advance by the peak position information storage means is based on an actual measurement value of the imaging lens.

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