JP2015045804A - Focus detection device, imaging device, focus detection method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detection device, an imaging device, a focus detection method and program that enable focus detection with less errors regardless of a color of a subject.SOLUTION: A focus detection device has: a first image pickup element that detects a light intensity distribution of an image to be formed by an imaging optical system for each wavelength area as to a plurality of wavelength areas; a second image pickup element that detects a light intensity distribution of a plurality of images to be formed by light passing through different areas of a pupil of the imaging optical system; and control means for calculating a defocus value on the basis of images to be output from the first image pickup element and the second image pickup element. The control means generates an image composed of a spatial frequency equal to or less than a spatial frequency corresponding to a pixel array pitch of the second image pickup element for the image to be output from the first image pickup element, and calculates the defocus value corrected on the basis of at least one of a ratio of intensity of light of a plurality of wavelength areas in the generated image and a ratio of a contrast thereof therein.

Description

  The present invention relates to a phase difference type focus detection device, an imaging device, a focus detection method, and a program.

  Recent imaging apparatuses are equipped with a focus detection device used for autofocus.

  In a phase difference detection type focus detection apparatus generally used in a single-lens reflex camera, a rotating mirror is a half mirror, and a light beam transmitted through the rotating mirror is reflected by a second reflecting mirror toward the lower part of the mirror box of the camera. Let Then, after passing through a condensing lens provided at a position substantially conjugated with the planned focal plane of the photographing optical system, the light beam from the condensing lens is guided to the secondary imaging optical system on the secondary imaging surface. Then, the subject image is re-imaged on the light receiving element arranged at the position.

  The secondary imaging optical system is provided as a pair (one pair) so that the entrance pupil corresponds to different portions of the exit pupil of the photographing optical system, and forms a set of subject images. The in-focus state is detected by measuring the relative positional deviation amount of these subject images.

  However, when the imaging position differs for each wavelength due to the chromatic aberration of the photographing lens, an error (focus shift) occurs in the detection result of the phase difference detection type focus detection device depending on the color of the subject. This error occurs because the color of the subject cannot be distinguished because the sensor of the focus detection device has only monochrome sensitivity.

  As shown in FIG. 3, when a plurality of color subjects (for example, petals and leaves) are included in the distance measurement area, since there are a plurality of best focus positions in one distance measurement area, only monochrome sensitivity is obtained. Without a sensor, an appropriate focal position cannot be detected.

  In Patent Document 1, a correction value is calculated by detecting a spectral intensity ratio of a subject color using a photometric sensor.

JP 2006-317595 A

  FIGS. 6A and 6B show output distributions when the subject is viewed through the imaging optical system with respect to the photometric sensor and the light receiving element of the phase difference detection type focus detection means. FIG. 7A is a diagram showing an output distribution of each color of a photometric sensor having spectral sensitivity in three wavelength regions of red, green, and blue (an example of spectral sensitivity is shown in FIG. 4).

  In FIG. 6A, since the maximum value of luminance is higher in the order of red, green, and blue, this subject has the most red reflected light, and the color that mainly constitutes this subject is red. On the other hand, the light receiving element of the focus detection means is a monochrome sensor having only a single color sensitivity, and is detected in a state where all the vibrations of luminance of red, green and blue are added. In the focus detection apparatus based on the phase difference detection method, the defocus amount is detected using the output distribution of FIG. In FIG. 6B, the color having the highest contrast among red, green, and blue is blue, and the color having the highest influence on the focus detection device is blue instead of red, which is a color mainly constituting the subject. .

  Further, as shown in FIG. 7, the same is true even when the amplitudes are all the same and the vibration frequencies are different. In the phase difference detection type focus detection means, a color having a high spatial frequency has a great influence on the detection result, so that the color having the highest influence on the focus detection means is blue.

  Therefore, it is only necessary to correct the difference from the color that should originally be focused by calculating the contrast for each color by the photometric sensor and determining the color that most affects the light receiving element of the focus detection means. However, when the sampling frequencies of the two types of image sensors of the photometric sensor and the light receiving element of the phase difference detection type focus detection means are different, an error occurs in the correction value.

  FIGS. 7A and 7B show the output distribution for each wavelength region when the subject is imaged by the photometric sensor, and the sum thereof. FIG. 7A shows a case where the central value of the pattern is the same for all colors, and FIG. 7B shows a case where the central value is different. FIG. 8 shows the output distribution when the output distribution of the photometric sensor in FIG. 7A is sampled at the sampling frequency of the light receiving element of the focus detection means.

  Here, it is assumed that the sampling frequency corresponding to the pixel arrangement pitch of the image sensor of the focus detection means is smaller than the sampling frequency corresponding to the pixel arrangement pitch of the image sensor as the photometric sensor.

  As shown in FIG. 7B, the blue contrast is the highest when sampling is performed at the sampling frequency of the photometric sensor. On the other hand, as shown in FIG. 8, when the output distribution of the photometric sensor is sampled at the sampling frequency of the light receiving element of the focus detection means, the red contrast is the highest. Therefore, the color having the greatest influence on the contrast detected by the focus detection means is red.

  As described above, when the sampling frequencies of the two types of image pickup devices are different, there is a possibility that the color having the most influence on the contrast output of the focus detection means may be mistaken, and there is a large chromatic aberration in red and blue regarding the image pickup optical system In this case, the focusing accuracy with respect to the subject is lowered.

  An object of the present invention is to provide a focus detection device, an imaging device, a focus detection method, and a program that can perform focus detection with little error regardless of the color of the subject.

  In order to achieve the above object, a focus detection apparatus according to the present invention includes a first imaging element that detects a light intensity distribution of an image formed by an imaging optical system for each of a plurality of wavelength regions, and the imaging A second image sensor that detects light intensity distributions of a plurality of images formed by light that has passed through different regions of the pupil of the optical system, and images that are output from the first image sensor and the second image sensor The focus detection apparatus includes a control unit that calculates a defocus value based on the first imaging element, the pixels of the first imaging element are arranged at a first pitch, and the pixels of the second imaging element are Arranged at a second pitch longer than the first pitch, the control means calculates a first defocus value based on a phase difference between a plurality of images formed on the second image sensor. And output from the first image sensor For the image, an image having a spatial frequency equal to or lower than the spatial frequency corresponding to the second pitch is generated, and based on at least one of a light intensity ratio and a contrast ratio in the plurality of wavelength regions in the generated image. The second defocus value is calculated by correcting the first defocus value.

  According to the present invention, focus detection with little error can be performed regardless of the color of the subject.

It is a figure which shows schematic structure of the imaging device carrying the focus detection apparatus which concerns on embodiment of this invention. It is the schematic of the focus detection means of a general phase difference detection system. It is a figure which shows an example of the to-be-photographed object in which several colors are mixed in the ranging area. It is a figure which shows an example of the spectral sensitivity of the sensor for photometry (1st image sensor) which concerns on embodiment of this invention. (A) is the figure shown about the algorithm selection method in the 1st Embodiment of this invention, (b) is the block diagram in the 1st Embodiment of this invention. (A) relates to an image sensor as a photometric sensor, and is a diagram showing an example of an output distribution obtained when viewing a subject having the same spatial frequency of the output distribution for each color but having a different contrast, and (b) is a focus detection. It is the figure which showed the spatial distribution of the output for every some sensitivity wavelength, and the thing which added them regarding the light receiving element of a means. (A) relates to an image sensor as a photometric sensor, an example of an output distribution for each color obtained when viewing a subject having the same contrast but a different spatial frequency of the output distribution, and (b) is a focus detection means. FIG. 6 is a diagram showing a spatial distribution of outputs for each of a plurality of sensitivity wavelengths and a sum of them for the light receiving element of FIG. It is an output distribution when the output distribution of FIG. 7A is sampled at the sampling frequency of the focus detection means.

<< First Embodiment >>
(Imaging device)
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an overall view of a focus detection apparatus and an imaging apparatus equipped with the focus detection apparatus according to an embodiment of the present invention. The imaging device is obtained by adding an imaging optical system to a focus detection device. In FIG. 1, a subject existing on the left side of the drawing is illuminated by light from a light source such as the sun, and reflects illumination light according to the reflection characteristics of the subject surface. The reflected light enters the imaging device from the imaging optical system 2 and forms an image in the vicinity of the imaging device 1 that captures the subject image.

  The image sensor 1 records the light distribution on the light receiving surface of the element and transfers it to the storage means. There is a main mirror 3 between the imaging element 1 and the imaging optical system, and a part of the total luminous flux that has passed through the imaging optical system 2 is reflected in a direction substantially perpendicular to the optical axis of the imaging optical system. The reflected light passes through the focusing plate 4 and passes through the pentaprism 5 and the eyepiece 6 and then forms an image. By looking at this image, the photographer can check the shooting screen. 7 is a photometric sensor for measuring the luminance value of the photographing screen. A photometric optical system 6 for condensing light on the light receiving surface of the photometric sensor 7 is disposed between the photometric sensor 7 and the pentaprism 5.

  In FIG. 1, photometry is performed by the photometric sensor 7 using light transmitted through the imaging lens 2 and the pentaprism 5, but the subject is directly observed without using the finder optical path and the imaging optical path as shown in FIG. Also good. The photometric sensor 7 as the first image sensor detects the color of the subject. Here, the color of the subject is the spectral intensity ratio within the visible region of the light reflected by the subject illuminated with the illumination light. A sub mirror 9 is arranged between the main mirror 3 and the image sensor 1. The sub mirror 9 reflects a part of the light transmitted through the main mirror 3 and guides it to the focus detection means 10.

(Focus detection device)
The focus detection apparatus of the present embodiment includes a first image sensor (photometric sensor 7 in FIG. 1), a second image sensor (light receiving elements 25 and 26 in FIG. 2), and the output of the first image sensor. Camera-side control means (not shown) that calculates a defocus value based on the output of the second image sensor is provided. Here, the second image sensor is a line sensor (one-dimensional image sensor) constituting the focus detection means 10 (FIG. 1) that obtains a defocus value by a phase difference detection method.

  Here, the photometric sensor 7 has a first pixel arrangement pitch (first pitch), and detects a light intensity distribution of an image formed by the imaging optical system for each of a plurality of wavelength regions. Further, the light receiving elements 25 and 26 have a second pixel arrangement pitch (second pitch) longer than the first pixel arrangement pitch described above. The light receiving elements 25 and 26 capture the subject without distinguishing the subject color via the imaging optical system, and obtain focus detection information by phase difference detection.

  A camera-side control unit (not shown) calculates a defocus value by detecting a phase difference between images acquired by the second imaging elements 25 and 26. Then, the camera-side control means drives the whole or a part of the imaging optical system 2 or the imaging element 1 in the optical axis direction based on the calculated defocus value via the imaging optical system control means 12.

  Here, the first image sensor (photometric sensor 7 in FIG. 1) has a first pixel arrangement pitch, and obtains intensity distribution information related to the color of the subject via the imaging optical system 2. The second image sensor (the light receiving elements 25 and 26 in FIG. 2) has a second pixel arrangement pitch that is different from the first pixel arrangement pitch, and does not distinguish the subject color through the imaging optical system. To obtain focus detection information by phase difference detection.

  The output from the first image sensor (photometric sensor 7) is converted from a first sampling frequency corresponding to the first pixel arrangement pitch to a second sampling frequency corresponding to the second pixel arrangement pitch. A second defocus value is calculated based on the output based on the second sampling frequency from the first image sensor and the output of the second image sensor.

  Here, in general, the sampling frequency of the light receiving element of the focus detection means is lower than the sampling frequency of the imaging element as the photometric sensor.

  As shown in FIG. 4, the photometric sensor 7 has a plurality of different sensitivity areas in the sensitivity area of the imaging device 1 and is a multi-division sensor that can detect the color distribution in the distance measurement area. The photometric sensor 7 compares the intensity distribution information of a plurality of wavelength regions generated in the distance measuring region, and selects a correction algorithm.

  FIG. 5A is a flowchart for selecting a correction algorithm, and FIG. 5B is a block diagram. Here, the output value of the mth pixel of the kth color component of the photometric sensor 7 is Akm, the output value of the nth pixel of the light receiving element 25 is Bn, and the sampling frequency of the photometric sensor 7 and the light receiving elements 25 and 26 is set. Let S and A respectively.

  First, the sampling frequency S of the photometric sensor 7 is compared with the sampling frequency A of the light receiving elements 25 and 26 of the focus detection means 10 (step 01).

  When the sampling frequency S of the photometric sensor 7 and the sampling frequency A of the light receiving elements 25 and 26 are different, the output distribution data obtained from the photometric sensor 7 is Fourier transformed into a frequency space (step 02).

  The component of the l-th frequency of the Fourier transform result is Akml. And the frequency component below the sampling frequency of the focus detection means 10 is extracted about the data which carried out the Fourier-transform (step 03).

  Next, the extracted data is subjected to inverse Fourier transform to obtain luminance distribution information made up of only low frequency components (step 04). In this way, as shown in FIG. 5B, the low-frequency component is generated from the captured image (output image) of the first image sensor (photometric sensor) through steps 02, 03, and 04 as shown in FIG. A generated image is output.

  Then, the brightness of the nth pixel of the kth color at this time is set to Akpn, and the color having the most contrast is selected from the data (step 05). Thereby, even if there is a difference in the sampling frequency described above, the color that has the most influence on the contrast output of the focus detection means is never mistaken.

  As a selection method, a method of selecting the largest color by taking the sum of the differential values of luminance data, a method of selecting the largest color by taking the difference between the maximum value and the minimum value of the output value of each color, etc. are used. it can.

  The defocus value corresponding to each color can be calculated using performance information such as chromatic aberration of the lens.

  In order to perform correction with higher accuracy, the following steps are provided. That is, the intensity ratio and contrast of light in a plurality of wavelength regions in an image having a spatial frequency equal to or lower than the spatial frequency corresponding to the second pitch (the generated image in FIG. 5B through steps 02, 03, and 04). Correction is performed using at least one of the ratios.

  If the subject light is substantially formed of a single color, high accuracy can be obtained by matching the dominant color described above. However, there are subjects in which a plurality of colors are mixed in the same degree. Therefore, correction is performed in accordance with the mixing ratio of the colors constituting the subject.

  Here, an example of correction will be described. First, the red, green, and blue contrast magnitudes when synchronized with the light receiving element of the focus detection means 10 are the defocus amounts output from the subjects of a, b, c, red, green, and blue, respectively, X, Let Y, Z.

  Then, the defocus amount D output by the defocus amount detection means 10 is D = (a * X + b * Y + c * Z) / (a + b + c). If the red, green, and blue intensities are Ar, Bg, and Cb, the best focus position D2 with the highest resolution is D2 = (Ar * X + Bg * Y + Cb * Z) / (Ar + Bg + Cb). Here, if the focus correction amount is set to the difference amount between D and D2, accurate focus detection correction can be performed.

  As described above, according to the present embodiment, it is possible to provide a focus detection apparatus and an imaging apparatus capable of focusing with a small focus detection error even when a plurality of colors exist in the subject region.

(Focus detection method and program)
Further, the present invention reduces errors by correcting the first defocus value calculated based on the phase difference between the plurality of images formed on the second image sensor using the first image sensor. The focus detection method for calculating the second defocus value includes the following.

  Detecting a light intensity distribution of an image formed by the imaging optical system using the first imaging element for each of a plurality of wavelength regions. Furthermore, the method includes a step of detecting light intensity distributions of a plurality of images formed by light that has passed through different regions of the pupil of the imaging optical system using the second imaging element. Here, the pixels of the first image sensor are arranged at a first pitch, and the pixels of the second image sensor are arranged at a second pitch that is longer than the first pitch.

  Further, a step of calculating a first defocus value based on a phase difference between a plurality of images formed on the second image sensor, and an image output from the first image sensor corresponds to the second pitch. Generating an image having a spatial frequency equal to or lower than the spatial frequency. Then, the second defocus value is calculated by correcting the first defocus value based on at least one of the light intensity ratio and the contrast ratio in the plurality of wavelength regions in the generated image. Steps.

  The present invention can also be realized by executing the following processing as a program. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

(Modification)
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

(Modification 1)
In the embodiment described above, focus detection correction is performed using the photometric sensor 7 as the first image sensor, but focus detection correction is performed using the image sensor 1 that captures an image of the subject as the first image sensor. Also good.

7 .. Photometric sensor (first image sensor) 10.. Focus detection means 12.. Imaging optical system control means (control means) 25, 26.

Claims (8)

A first imaging element that detects a light intensity distribution of an image formed by the imaging optical system for each of a plurality of wavelength regions;
A second imaging element that detects light intensity distributions of a plurality of images formed by light that has passed through different regions of the pupil of the imaging optical system;
A focus detection apparatus including a control unit that calculates a defocus value based on images output from the first image sensor and the second image sensor;
The pixels of the first image sensor are arranged at a first pitch, and the pixels of the second image sensor are arranged at a second pitch longer than the first pitch,
The control means calculates a first defocus value based on a phase difference between a plurality of images formed on the second image sensor, and outputs the second defocus value for the image output from the first image sensor. Generating an image having a spatial frequency equal to or lower than the spatial frequency corresponding to the pitch of the first defocus based on at least one of a light intensity ratio and a contrast ratio in the plurality of wavelength regions in the generated image A focus detection apparatus that calculates a second defocus value by correcting the value.   The control means performs Fourier transform on the image output from the first image sensor, extracts a component having a spatial frequency or less corresponding to the second pitch, and corresponds to the extracted second pitch. The focus detection apparatus according to claim 1, wherein an image having a spatial frequency equal to or lower than the spatial frequency corresponding to the second pitch is generated by performing inverse Fourier transform on a component equal to or lower than the spatial frequency.   The focus detection apparatus according to claim 1, wherein the first image sensor is a photometric sensor.   The focus detection apparatus according to claim 1, wherein the first image sensor is an image sensor that images a subject.   The focus detection apparatus according to claim 1, wherein the second image sensor is a plurality of line sensors.   An imaging apparatus comprising: the focus detection apparatus according to claim 1; and the imaging optical system. Detecting a light intensity distribution of an image formed by the imaging optical system for each wavelength region for each wavelength region using the first imaging element in which pixels are arranged at a first pitch; and
Light intensity of a plurality of images formed by light passing through different regions of the pupil of the imaging optical system using a second imaging element in which pixels are arranged at a second pitch longer than the first pitch Detecting a distribution;
Calculating a first defocus value based on a phase difference between a plurality of images formed on the second image sensor;
Generating an image having a spatial frequency equal to or lower than a spatial frequency corresponding to the second pitch for the image output from the first imaging element;
Calculating a second defocus value by correcting the first defocus value based on at least one of a light intensity ratio and a contrast ratio in the plurality of wavelength regions in the generated image; and ,
A focus detection method comprising: In the computer of the focus detection device,
Detecting a light intensity distribution of an image formed by the imaging optical system for each wavelength region for each wavelength region using the first imaging element in which pixels are arranged at a first pitch; and
Light intensity of a plurality of images formed by light passing through different regions of the pupil of the imaging optical system using a second imaging element in which pixels are arranged at a second pitch longer than the first pitch Detecting a distribution;
Calculating a first defocus value based on a phase difference between a plurality of images formed on the second image sensor;
Generating an image having a spatial frequency equal to or lower than a spatial frequency corresponding to the second pitch for the image output from the first imaging element;
Calculating a second defocus value by correcting the first defocus value based on at least one of a light intensity ratio and a contrast ratio in the plurality of wavelength regions in the generated image; and ,
A program characterized by having executed.