JP2013258602A - Image pick-up device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand the dynamic range, without reducing the spatial resolution to 1/2.SOLUTION: The image pick-up device includes an image pick-up lens for condensing light from a subject, an image sensor 10 for detecting an image signal by capturing the light condensed by the image pick-up lens, and a microlens array 9 arranged between the image sensor 10 and the image pick-up lens at an interval in the optical axis direction for the focal plane B of the image pick-up lens. The microlens array 9 includes a plurality of microlenses 9a, 9b which condense and focus the incident light, respectively, on the image pick-up surface of the image sensor 10. Two types or more of microlenses 9a, 9b having different effective diameter, focal length and transmittance are arranged in array in a direction crossing the optical axis.

Description

  The present invention relates to an imaging apparatus.

2. Description of the Related Art Conventionally, an imaging apparatus that can acquire an image with a high dynamic range using a microlens array is known (see, for example, Non-Patent Document 1).
This imaging device provides different filters to each microlens to vary the amount of light passing through each microlens, thereby obtaining an image with a large exposure amount and an image with a small exposure amount in one shot, and these images. Are combined to obtain an image with a high dynamic range.

New results on the Plenoptic 2.0 camera. Georgiev, T, Signals, Systems and Computers, 2009 Conference Record of the Forty-Third Asilomar Conference, Page1243-1247

  However, since the imaging apparatus of Non-Patent Document 1 attempts to expand the dynamic range by providing different filters to the microlenses having the same size and varying the exposure conditions, the spatial resolution is at least 1/2. There is an inconvenience that it must be lowered.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an imaging apparatus capable of expanding the dynamic range without reducing the spatial resolution to ½.

In order to achieve the above object, the present invention provides the following means.
One embodiment of the present invention includes an imaging lens that collects light from a subject, an imaging element that captures light collected by the imaging lens and detects an image signal, and the imaging element and the imaging lens. And a microlens array disposed with a gap in the optical axis direction with respect to the focal plane of the imaging lens, and the microlens array collects incident light and images the imaging element Provided is an imaging device in which two or more types of microlenses that form images on a surface and have different effective diameters, focal lengths, and transmittances are arranged in an array in a direction intersecting the optical axis To do.

  According to this aspect, the light from the subject condensed by the imaging lens forms a real image on the focal plane of the imaging lens, and then the microlens is arranged with an interval in the optical axis direction with respect to the focal plane. The light is incident on the array and is individually imaged on the imaging surface of the imaging device by each microlens constituting the microlens array. Accordingly, a plurality of images of the subject are acquired for each microlens in the image sensor.

  In this case, according to the imaging apparatus according to this aspect, since the microlens array is configured by arranging a plurality of types of microlenses having different effective diameters, the resolution is high due to the microlenses having a large effective diameter. An image can be acquired, and an image with low resolution is acquired by a microlens having a small effective diameter. Therefore, an image with high resolution can be acquired by matching the focal plane of the imaging lens with the focal plane of the microlens having a large effective diameter.

In this case, the focal plane of a microlens with a small effective diameter with a different focal length does not coincide with the focal plane of the imaging lens, so that the acquired image signal does not contribute to the improvement of resolution, but passes through microlenses with different transmittance. The dynamic range can be improved by the plurality of image signals having different exposure conditions.
Compared with a conventional imaging device in which microlenses with the same effective diameter are arranged by making the effective diameter of the microlens that does not contribute to the improvement in resolution smaller than the effective diameter of the microlens for acquiring a high-resolution image. Thus, the dynamic range can be improved without reducing the resolution to ½, that is, while suppressing the resolution.

In the above aspect, the micro lens array may include two types of micro lenses having different effective diameters and focal lengths, and the micro lens having a smaller effective diameter may have at least two types of transmittance. .
By doing so, the dynamic range can be improved only by the microlens having the smaller effective diameter, and a bright image having a high resolution can be obtained by the microlens having the larger effective diameter.

Further, in the above aspect, the microlenses having different transmittances are arranged at positions where light from a subject that has passed through the same region on their focal planes is incident on both microlenses. Also good.
By doing in this way, it is possible to photograph with the imaging element with different exposure conditions for the light passing through the same region, and the dynamic range can be improved.

Moreover, in the said aspect, the said micro lens with a larger effective diameter may have at least 2 types of polarization directions.
By doing in this way, the image signal of at least one polarization component can be reconstructed using the image signal detected by the image sensor assigned to the micro lens having the same polarization direction. As a result, for example, an image in which glare caused by reflected light is suppressed can be acquired.

  Further, in the above aspect, the first image constituting unit constituting the image signal detected by the imaging device assigned to the micro lens having the larger effective diameter and the micro lens having the smaller effective diameter A second image constructing unit constituting an image signal detected by the assigned image sensor, an image signal constructed by the first image constructing unit, and an image constructed by the second image constructing unit. You may provide the image synthetic | combination part which synthesize | combines a signal.

  By doing so, an image signal with high resolution is configured by the first image configuration unit, an image signal that improves the dynamic range is configured by the second image configuration unit, and the resolution is reduced by the image synthesis unit. It is possible to acquire an image with improved dynamic range while suppressing it.

In the above aspect, the microlens array may be formed by arranging two types of microlenses so that one type of the microlenses is sandwiched between the other types of microlenses.
By doing in this way, the dynamic range of the image with high resolution at the position of the microlens with the larger effective diameter can be improved by the image at the position of the microlens with the smaller effective diameter that sandwiches the dynamic range.

In the above aspect, the microlens array may be formed by arranging two types of microlenses so that one type of the microlenses is sandwiched by two other types of microlenses from two different directions. .
By doing so, the dynamic range of the high-resolution image at the position of the microlens with the larger effective diameter can be more reliably improved by the image at the position of the microlens with the smaller effective diameter that sandwiches the dynamic range. Can do.

Moreover, in the said aspect, you may provide the light-shielding member which shields so that the light which passed through one of the said microlenses may enter into the pixel corresponding to the said adjacent microlens.
By doing in this way, the light which passed through the adjacent microlens is shielded by the light shielding member, and it is possible to prevent the occurrence of crosstalk mixed on the image sensor.

  According to the present invention, there is an effect that the dynamic range can be expanded without reducing the spatial resolution to ½.

1 is an overall configuration diagram illustrating an imaging apparatus according to an embodiment of the present invention. It is a front view which shows an example of the micro lens array with which the imaging device of FIG. 1 was equipped. It is a longitudinal cross-sectional view which shows the DD cross section in FIG. 2 of the micro lens array of FIG. It is a block diagram which shows the detail of the reconstruction part with which the imaging device of FIG. 1 was equipped. It is a longitudinal cross-sectional view explaining the 1st modification of the micro lens array of FIG. It is a longitudinal cross-sectional view explaining the 2nd modification of the micro lens array of FIG. It is a front view explaining the 1st modification of the arrangement | sequence of the micro lens array of FIG. It is a front view explaining the 2nd modification of the arrangement | sequence of the micro lens array of FIG. It is a front view explaining the 3rd modification of the arrangement | sequence of the micro lens array of FIG. It is a front view explaining the 4th modification of the arrangement | sequence of the micro lens array of FIG. It is a front view explaining the 5th modification of the arrangement | sequence of the micro lens array of FIG. It is a front view explaining the 6th modification of the arrangement | sequence of the micro lens array of FIG. It is a front view explaining the 7th modification of the arrangement | sequence of the micro lens array of FIG.

An imaging apparatus 1 according to an embodiment of the present invention will be described below with reference to the drawings.
As illustrated in FIG. 1, the imaging apparatus 1 according to the present embodiment includes an imaging unit 2 that captures an image of a subject A, an image processing unit 3 that processes an image signal acquired by the imaging unit 2, and an imaging unit 2. A control unit 5 that controls the image processing unit 3 and the imaging control unit 4, and an I / F unit 6 that inputs an external signal to the control unit 5.

  The imaging unit 2 includes, in order from the subject A side, an imaging lens 7 disposed facing the subject A, an aperture stop 8 that determines a light beam diameter of light that has passed through the imaging lens 7, and a rear side of the imaging lens 7. A microlens array 9 disposed at a distance in the direction away from the subject A in the optical axis direction with respect to the real image B formed at the focal position, and further spaced apart in the optical axis direction with respect to the microlens array 9. And an image sensor 10 that captures light that has passed through the microlens array 9.

  An AF motor 11 is connected to the imaging lens 7. The imaging lens 7 is moved in the optical axis direction by driving the AF motor 11 in accordance with a command signal from the imaging control unit 4 so that the front focal point coincides with the subject A. In FIG. 1, the imaging lens 7 is displayed as a single lens, but actually includes a plurality of lenses arranged in the optical axis direction, and at least one lens is aligned in the optical axis direction by the AF motor 11. Can be moved to.

  An opening adjustment motor 12 is connected to the aperture stop 8. The aperture stop 8 is configured such that the opening degree is adjusted by driving the opening degree adjusting motor 12 in accordance with a command signal from the imaging control unit 4 so that the amount of incident light is adjusted. The aperture stop 8 is adjusted so that an image signal acquired by a later-described larger microlens 9a is properly exposed.

As shown in FIGS. 2 and 3, the microlens array 9 is configured by alternately arranging two types of microlenses 9a and 9b having different diameters in the diameter direction. These two types of microlenses 9a and 9b have different focal lengths and effective diameters.
In FIG. 3, reference numeral 13 denotes a light shielding member that partitions a space between the microlens array 9 and the image sensor 10 so that crosstalk does not occur on the image sensor 10.

As the larger microlens 9a, one having the same transmittance so as to achieve proper exposure is used.
Further, there are two types of microlenses 9b having different transmittances, and the microlens 9b having a high transmittance and the microlens 9b having a low transmittance (shown by hatching in the drawing) are larger. They are arranged in a positional relationship with the micro lens 9a interposed therebetween. The microlens 9b having the higher transmittance is set to a transmittance that is over with respect to the proper exposure, and the microlens 9b having the smaller transmittance is set to be under the appropriate exposure.

  By arranging in this way, the larger microlens 9a is surrounded by the smaller microlens 9b, and at the same time, the smaller microlens 9b is also surrounded by the larger microlens 9a. It has become.

As a result, one type of microlens 9a (9b) is sandwiched by the other type of microlens 9b (9a) from two directions, up, down, left, and right.
3 is a cross-sectional view taken along the line DD of FIG.
According to FIG. 3, the focal plane B of the larger micro lens 9 a coincides with the rear focal position of the imaging lens 7. On the other hand, the focal plane C of the smaller microlens 9b is arranged at a position shifted from the focal position of the imaging lens 7 toward the subject A in the optical axis direction.

Further, as shown in FIG. 3, the two microlenses 9b disposed at the positions sandwiching the larger microlens 9a are such that the light that has passed through any position on the focal plane C thereof is the two microlenses 9b. These are arranged so as to be incident on any of the above.
The image sensor 10 is, for example, an RGB primary color single-plate CCD.

  As shown in FIG. 1, the image processing unit 3 temporarily stores an A / D converter 14 that converts an image signal detected by the image sensor 10 into a digital signal, and an image signal converted into a digital signal. A buffer 15 for processing, a signal processing unit 16 for processing a single-plate image signal stored in the buffer 15 to generate a three-plate image signal, and an image signal generated by the signal processing unit 16 And a reconstruction unit 17 for reconstructing the signal.

  The signal processing unit 16 reads a single-plate image signal on the buffer 15 based on a command signal from the control unit 5, and performs three plates from the image signal of each pixel after performing known demosaicing processing and white balance processing. A state image signal is generated.

As shown in FIG. 4, the reconstruction unit 17 temporarily stores the image signal generated by the signal processing unit 16, and reconstructs the image signal based on the image signal stored in the buffer 18. An image reconstruction unit (first image configuration unit) 19 to be configured, an HDR reconstruction unit (second image configuration unit) 20 to reconstruct an image signal having a high dynamic range, and an image reconstruction unit 19 to perform reconstruction The image compositing unit 21 synthesizes the reconstructed image signal Sn and the image signal S _HDR reconstructed by the HDR reconstruction unit 20.

  More specifically, the image reconstruction unit 19 uses the image signal acquired by the pixel region of the image sensor 10 assigned to the larger microlens 9a among the image signals stored in the buffer 18. The image signal Sn is generated. In the example shown in FIG. 3, the magnification of the larger microlens 9a is 1/3, but the effective diameter is twice that of the smaller microlens 9b. The resolution of the image signal Sn is 2/3 in both vertical and horizontal directions.

On the other hand, the HDR reconstruction unit 20 uses the image signal acquired from the pixel region of the image sensor 10 allocated to the smaller microlens 9b among the image signals stored in the buffer 18, and has a dynamic range. A high image signal S _HDR is generated.

When the under and over image signals acquired from the pixel area assigned to each micro lens 9b are Su and So, and the under and over transmittances of the micro lens 9b are Tu and To, respectively, the HDR reconstruction unit The image signal S _HDR generated at 20 is
S _HDR = Su / Tu + So / To
It becomes.
In the example shown in FIG. 3, since the magnification of the smaller microlens 9b is 1/6, the resolution of the image signal is 1/6 in both vertical and horizontal directions.

In the image composition unit 21, the resolution of the image signal S _HDR output from the HDR reconstruction unit 20 is doubled vertically and horizontally using known bilinear interpolation or bicubic interpolation to obtain an image signal S _HDR ′. In addition, the obtained image signal S _HDR 'is added to the image signal Sn generated by the image reconstruction unit 19 to synthesize the image signal S.
S = Sn + S _HDR '

The operation of the imaging apparatus 1 according to the present embodiment configured as described above will be described below.
In order to perform shooting using the imaging apparatus 1 according to the present embodiment, after setting shooting conditions such as ISO sensitivity and exposure via the I / F unit 6, a shutter button (not shown) is half-pressed. Enter pre-shoot mode. Light from the subject A enters the imaging unit 2 via the imaging lens 7, forms a real image B, and then is collected by the microlens array 9 and photographed by the imaging device 10. The image signal acquired by the image sensor 10 is converted into a digital signal by the A / D converter 14 and then transferred to and stored in the buffer 15.

  The image signal stored in the buffer 15 is sent to the imaging control unit 4. The imaging control unit 4 controls the opening adjustment motor 12 of the aperture stop 8 using the luminance level in the transmitted image signal, and controls the electronic shutter speed in the imaging element 10. Further, the imaging control unit 4 controls the AF motor 11 of the imaging lens 7 to calculate a contrast value in a predetermined region from the image signal, and sets the imaging lens 7 to a predetermined focal length so that the contrast value is maximized. Set.

  In this state, the full shooting is performed by fully pressing the shutter button. The actual photographing is performed based on the focal length and the exposure condition obtained by the imaging control unit 4, and the acquired image signal is converted into a digital signal by the A / D converter 14, transferred to the buffer 15, and stored. Is done. Thereafter, the image signal in the buffer 15 is transferred to the signal processing unit 16.

  In the signal processing unit 16, a three-plate image signal of each pixel RGB is generated by performing known demosaicing processing and white balance processing on the single-plate image signal transferred from the buffer 15. . The generated image signal is transferred to the reconstruction unit 17.

  In the reconstruction unit 17, the image signal sent from the signal processing unit 16 is stored in the buffer 18. Then, the image signal acquired in the pixel region of the image sensor 10 assigned to the larger microlens 9a among the image signals stored in the buffer 18 is input to the image reconstruction unit 19, and the smaller one is input. An image signal acquired in the pixel region of the image sensor 10 assigned to the microlens 9 b is input to the HDR reconstruction unit 20.

In the image reconstruction unit 19, an image signal Sn having a relatively high resolution and a low dynamic range is reconstructed based on the input image signal. On the other hand, the HDR reconstruction unit 20 reconstructs an image signal S _HDR 'having a low resolution and a high dynamic range based on the input image signal.

In this case, since the focal plane C of the smaller microlens 9b is shifted in the optical axis direction from the rear focal position B of the imaging lens 7, it depends on the pixel area of the imaging element 10 assigned to the microlens 9b. The acquired image signal does not contain high resolution information. However, since the dynamic range information is sufficiently included, the HDR reconstruction unit 20 can reconstruct the image signal S _HDR ′ having a low resolution and a high dynamic range.

The reconstructed image signals Sn and S _HDR ′ are input to the image synthesis unit 21 and added there to output an image signal S having a relatively high resolution and a high dynamic range. it can.

In other words, according to the imaging apparatus 1 according to the present embodiment, the image signal Sn having a relatively high resolution and a low dynamic range and the image signal S _HDR 'having a low resolution and a high dynamic range are combined to obtain a relatively high resolution. An image signal S having a high dynamic range can be obtained. That is, when the exposure conditions are changed by providing different filters to microlenses having the same size as in the prior art, the resolution is reduced to ½, whereas in the imaging apparatus according to the present embodiment, According to this, there is an advantage that the image signal Sa having a high dynamic range can be obtained without reducing the resolution to 2/3 and to 1/2.

In the present embodiment, the larger microlens 9a is exemplified as having the same transmittance. However, as shown in FIG. 5, those having different polarization directions (in the drawing, the hatching direction in the microlens 9a). The difference indicates the difference in the polarization direction.) May be alternately arranged.
In this case, the light passing through each region on the imaging plane of the imaging lens 7 is configured to be incident on either of the two microlenses 9a having different polarization directions.

The image reconstruction unit 19 outputs two types of image signals Ss and Sp having different polarization directions. In the image composition unit 21, these and S _HDR ′ output from the HDR reconstruction unit 20 are respectively output. By synthesizing, the following two types of image signals S1 and S2 can be obtained.
S1 = Ss + S _HDR '
S2 = Sp + S _HDR '

By doing so, the image signal from the image reconstruction unit 19 is separated into two types of image signals Ss and Sp having different polarization directions, so the resolution becomes one third of the half of the above embodiment. When the micro lens having the same effective diameter is to be realized, the resolution is 1/4, so that there is an advantage that the dynamic range can be improved with a higher resolution.
Then, by obtaining image signals having different polarization directions in this way, it is possible to remove specific reflected light components from the image, and an image with less glare can be obtained.

  In the present embodiment, two types of microlenses 9b having different transmittances are provided as the smaller microlens 9b. Instead, as shown in FIG. 6, the larger microlens 9b is provided. The transmittance of the lens 9a may be set to appropriate exposure, and the smaller microlens 9b may be set to have a transmittance that exceeds the appropriate exposure. In this case, although the increase amount of the dynamic range is small, the resolution can be set to 1 / 2.5.

  In the present embodiment, the microlenses 9a and 9b are exemplified by the arrangement and shape as shown in FIG. 2, but instead of this, any arrangement and shape as shown in FIGS. It may be adopted.

A subject B focal plane 1 imaging device 7 imaging lens 9 microlens array 9a, 9b microlens 10 imaging element 13 light shielding member 19 image reconstruction unit (first reconstruction unit)
20 HDR reconstruction unit (second reconstruction unit)
21 Image composition part

Claims (8)

An imaging lens that collects light from the subject;
An image sensor that detects an image signal by photographing the light collected by the imaging lens;
A microlens array disposed between the image pickup element and the image pickup lens with an interval in the optical axis direction with respect to a focal plane of the image pickup lens;
The microlens array is a plurality of microlenses that collect incident light and form images on the imaging surface of the imaging device, respectively, and two or more types of microlenses having different effective diameters, focal lengths, and transmittances An image pickup apparatus formed by arraying in a direction intersecting the optical axis. The microlens array includes two types of microlenses having different effective diameters and focal lengths,
The imaging device according to claim 1, wherein the microlens having a smaller effective diameter has at least two types of transmittance.   The imaging according to claim 2, wherein the microlenses having different transmittances are arranged at positions where light from a subject that has passed through the same region on their focal planes enters both of the microlenses. apparatus.   The imaging device according to claim 2 or 3, wherein the microlens having a larger effective diameter has at least two types of polarization directions. A first image constituting unit constituting an image signal detected by the imaging element assigned to the micro lens having a larger effective diameter;
A second image constituting unit constituting an image signal detected by the imaging element assigned to the micro lens having a smaller effective diameter;
5. The image synthesizing unit according to claim 2, further comprising an image synthesizing unit that synthesizes the image signal configured by the first image configuration unit and the image signal configured by the second image configuration unit. Imaging device.   The imaging according to any one of claims 2 to 5, wherein the microlens array is formed by arranging two types of microlenses so that one type of the microlenses is sandwiched between the other types of microlenses. apparatus.   6. The microlens array according to any one of claims 2 to 5, wherein the microlens array is formed by arranging two types of microlenses so as to sandwich one type of the microlenses between the other types of microlenses from two different directions. The imaging device described in 1.   The imaging device according to claim 1, further comprising: a light shielding member that shields light that has passed through any one of the microlenses from entering a pixel corresponding to the adjacent microlens.

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