BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging device, and more particularly, to an imaging device that independently acquires three images with one imaging element.

2. Description of the Related Art

JP2009-169096A discloses an imaging device in which a pupil region of an optical system is divided into two regions and light transmitted through each region is separated by a polarizer and an analyzer and is received by different pixels, which makes it possible to independently acquire two images with one imaging element. However, the number of images that can be acquired by the imaging device disclosed in JP2009-169096A is limited to two.

On the other hand, WO2012/143983A discloses an imaging device in which a pupil portion of an optical system is divided into two or more regions and light from each region is guided to different pixels by a microlens array, which makes it possible to independently acquire two or more images with one imaging element.

However, the separation of beams by the microlens array is not always perfect. Therefore, the imaging device disclosed in WO2012/143983A has a problem that light leaks to adjacent pixels and crosstalk occurs.

In order to solve this problem, WO2015/004886A proposes a technique that performs predetermined signal processing on a signal (pixel signal) obtained from each pixel to remove the influence of crosstalk.

SUMMARY OF THE INVENTION

However, the amount of crosstalk occurring in each pixel in a case in which beams are separated by the microlens array varies depending on the position of the pixels. Therefore, in the imaging device disclosed in WO2015/004886, it is necessary to calculate the amount of crosstalk occurring in each pixel in order to obtain a higher-quality image. However, this requires a great deal of effort.

The invention has been made in view of the above-mentioned problems, and an object of the invention is to provide an imaging device that can acquire three independent high-quality images using one imaging element.

(1) There is provided an imaging device comprising: an optical system including three optical regions that transmit light in different polarization directions; an imaging element including a plurality of pixel units each of which is a set of N pixels that receive light in different polarization directions, where N is an integer satisfying N≥3; a storage unit that stores a coefficient group configured by a matrix A of 3 rows and N columns in which each element is represented by aij, where i is an integer satisfying 1≤i≤3 and j is an integer satisfying 1≤j≤N; and an arithmetic unit that acquires the coefficient group from the storage unit and calculates three pixel signals X1, X2, and X3corresponding to each of the optical regions of the optical system from N pixel signals x1, x2, . . . , xN obtained from each of the pixel units of the imaging element using the following expression.

[X⁢⁢1X⁢⁢2X⁢⁢3]=[a⁢⁢11a⁢⁢12⋯a⁢⁢1⁢Na⁢⁢21a⁢⁢22⋯a⁢⁢2⁢Na⁢⁢31a⁢⁢32⋯a⁢⁢3⁢N]*[x⁢⁢1x⁢⁢2⋮xN]

According to this aspect, predetermined arithmetic processing is performed on the N pixel signals x1, x2, . . . , xN obtained from each pixel unit of the imaging element to obtain the pixel signals X1, X2, and X3corresponding to each optical region of the optical system. Therefore, it is possible to acquire three independent high-quality images using one imaging element.

(2) In the imaging device according to (1), the matrix A may be acquired by calculating an inverse matrix of a matrix that has, as an element, a ratio at which light incident on each of the optical regions of the optical system is received by each of the pixels of each of the pixel units of the imaging element.

According to this aspect, an inverse matrix B−1of a matrix B having, as an element, the ratio at which the light incident on each optical region of the optical system is received by each pixel of each pixel unit of the imaging element is calculated to acquire each element of the matrix A.

(3) In the imaging device according to (2), the ratio at which the light incident on each of the optical regions of the optical system is received by each of the pixels of each of the pixel units of the imaging element may be acquired by calculating a square of a cosine of an angular difference between the polarization direction of light transmitted through each of the optical regions of the optical system and the polarization direction of light received by each of the pixels of each of the pixel units of the imaging element.

According to this aspect, the square of the cosine of the angular difference between the polarization direction of the light transmitted through each optical region of the optical system and the polarization direction of the light received by each pixel of each pixel unit of the imaging element is calculated to calculate each element of the matrix B.

(4) In the imaging device according to any one of (1) to (3), the imaging element may include a plurality of the pixel units each of which is a set of three pixels that receive light in different polarization directions.

According to this aspect, one pixel unit is composed of three pixels whose number is equal to the number of divisions of the optical region.

(5) In the imaging device according to any one of (1) to (3), a combination of the polarization directions of the light transmitted through each of the optical regions of the optical system may be the same as a combination of the polarization directions of the light received by each of the pixels of each of the pixel units of the imaging element.

According to this aspect, the combination of the polarization directions of the light transmitted through each optical region of the optical system and the combination of the polarization directions of the light received by each pixel of each pixel unit of the imaging element have the same setting. Therefore, it is possible to simplify the arithmetic processing in a case in which each element of the matrix A is calculated.

(6) In the imaging device according to any one of (1) to (5), the optical system may include three polarization filters having different polarization directions which are provided at a pupil position.

According to this aspect, three polarization filters having different polarization directions are provided at the pupil position.

(7) In the imaging device according to any one of (1) to (6), the optical regions of the optical system may have different focal lengths.

According to this aspect, the optical regions of the optical system have different focal lengths.

(8) In the imaging device according to any one of (1) to (6), the optical regions of the optical system may focus on objects at different distances.

According to this aspect, the optical regions of the optical system focus on the objects at different distances.

(9) In the imaging device according to any one of (1) to (6), the optical regions of the optical system may transmit light in different wavelength bands.

According to this aspect, the optical regions of the optical system transmit light in different wavelength bands.

(10) In the imaging device according to any one of (1) to (6), the optical regions of the optical system may have parallax therebetween.

According to this aspect, the optical regions of the optical system have parallax therebetween.

(11) In the imaging device according to any one of (1) to (6), at least two of the optical regions of the optical system may have parallax.

According to this aspect, at least two of the three optical regions of the optical system have parallax. For example, the two optical regions are set to the same focal length and have horizontal parallax.

(12) In the imaging device according to any one of (1) to (11), the imaging element may include a polarization element that is provided in each of the pixels.

According to this aspect, the polarization element is comprised in each pixel.

(13) In the imaging device according to (12), in the imaging element, the polarization element may be provided between a photodiode and a microlens which constitute each of the pixels.

According to this aspect, the polarization element is provided between the photodiode and the microlens constituting each pixel.

According to the invention, it is possible to independently acquire three high-quality images with one imaging element.

