JP2014016309A - Distance measuring device and distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a distance measuring device capable of performing appropriate distance estimation despite of subject distances largely different depending on the cases.SOLUTION: A distance measuring device comprises: an imaging lens 1 that allows incident of object light from a subject; a lens array 2 on which the object light transmitted through the imaging lens 1 is made incident; an imaging element 5 that receives the light passed through the lens array 2, and outputs image information; and an arithmetic device 6 that performs estimation of a distance to the subject. The lens array 2 is formed by two-dimensionally arraying microlenses 3 variable in focal distance; the imaging element 5 has a plurality of light-receiving elements corresponding to each of the microlenses 3; and the arithmetic device 6 performs distance estimation on the basis of the image information.

Description

  The present invention relates to a distance measuring device and a distance measuring method.

It is known to estimate a subject distance from light field information acquired by a “plenoptic camera” in which a lens array is incorporated in a normal camera optical system.
That is, Patent Document 1 and Non-Patent Document 1 disclose “apparatus for measuring a subject distance by the configuration of a plenoptic camera”.
Such a distance measuring device is used for “measurement of workpiece distance” of an industrial robot.

  The devices described in these documents cannot be said to have a sufficiently wide “range of subject distance for obtaining a favorable result” because the microlenses constituting the lens array have a fixed focal length.

  Non-Patent Document 2 describes that a range of measurable subject distances is expanded by configuring a lens array with “microlenses having different focal lengths”.

  However, in this case as well, since the focal lengths of the individual microlenses constituting the lens array are fixed, there is a limit to “expansion of the measurement range” of the subject distance.

  An object of the present invention is to realize a distance measuring device and a distance measuring method capable of performing a preferable distance estimation even when subject distances are greatly different.

  The distance measuring device according to the present invention receives an image pickup lens for entering object light from a subject, a lens array for entering object light transmitted through the image pickup lens, and light passing through the lens array to obtain image information. It has an image sensor that outputs and an arithmetic unit that estimates the distance to the subject. The lens array is a two-dimensional array of microlenses that can vary the focal length, and each image sensor corresponds to each microlens. The arithmetic unit has a plurality of light receiving elements, and performs the distance estimation based on the image information.

  The distance measuring method of the present invention is a distance measuring method using the distance measuring device, wherein a macro pixel is obtained from outputs of a plurality of light receiving elements corresponding to each micro lens, and the macro pixel and surrounding macro pixels are used. A step of extracting and creating a plurality of two-dimensional images for calculating the shift amount from the configured macropixel group, a step of calculating shift amounts of the plurality of two-dimensional images extracted and created by pattern matching, According to the focal length, the imaging distance is estimated based on a predetermined relationship between the shift amount and the imaging distance.

In the distance measuring apparatus / distance measuring method of the present invention, the focal length of the microlens in the lens array can be adjusted as described above.
Therefore, even when the subject distance is greatly different, it is possible to estimate a suitable distance by setting the “focal length suitable for the subject distance”.

It is a figure for demonstrating one Embodiment of a distance measuring device. It is a figure for demonstrating extraction and formation of a two-dimensional image from a macro pixel group. It is a figure for demonstrating two two-dimensional images which have a shift amount. It is a figure which shows two examples of the relationship between the amount of shifts, and object distance. It is a figure for demonstrating the process of distance measurement. It is a figure for demonstrating another form of implementation of a distance measuring device. It is a figure for demonstrating extraction and formation of a two-dimensional image from a macro pixel group. It is a figure for demonstrating the process of another distance measurement. It is a block diagram which shows one example of a structure of an arithmetic unit.

Hereinafter, embodiments will be described.
FIG. 1 shows the configuration of the distance measuring device.

In FIG. 1, reference numeral 1 denotes an “imaging lens”, reference numeral 2 denotes a “lens array”, reference numeral 3 denotes a “microlens”, reference numeral 5 denotes an “imaging device”, and reference numeral 6 denotes an “arithmetic device”.
A “plenoptic camera” can be constructed with the configuration shown in the figure.

A subject (not shown) for distance measurement is on the left side of the imaging lens 1 in FIG. Object light from the subject enters the imaging lens 1.
Object light that has passed through the imaging lens 1 enters the lens array 2, and light that has passed through the lens array 2 enters the imaging device 5.
The lens array 2 is arranged in a predetermined position with respect to the imaging lens 1, for example, in accordance with the image side focal plane position of the imaging lens 1.
In this case, an “image of an object at infinity” is formed on the imaging lens 1 at the position of the lens array 2.

The image sensor 5 outputs “image information” according to the incident light.
The arithmetic device 6 obtains image information output from the image sensor 5 and estimates the distance of the subject.

  The arithmetic device 6 has a microcomputer such as a CPU as an arithmetic unit, and performs various arithmetic operations and controls.

The microlens 3 constituting the lens array 2 can change the focal length.
Conventionally, various lenses that can change the focal length are known.
The microlens 3 used in the lens array 2 in FIG. 1 is an “electrowetting lens that changes the focal length by changing the applied voltage”.

  The electrowetting lens can change the radius of curvature of the lens surface by changing the applied voltage applied thereto, thereby changing the focal length.

  FIG. 1A shows a case where the focal length of the microlens 3 is large, and FIG. 1B shows a case where a “small focal length” is realized by reducing the radius of curvature of the microlens 3.

  The individual microlenses 3 and the image pickup device 5 are shielded from each other by a “light-shielding wall”, and the light passing through one microlens 3 is incident on a light receiving region indicated by reference numeral 4.

The light receiving region 4 corresponding to each microlens 3 has a plurality of light receiving elements.
Hereinafter, the image information output from the image sensor 5 is referred to as a “light field image”.
Of course, the light field image is not an actual visible image, but a “collected electric signal set” output from each light receiving element of the imaging element 5.

Since there is no fear of confusion, each light receiving element in the image sensor 5 will be referred to as a “pixel” hereinafter.
The “pixel” may mean an “electric signal” output from the light receiving element.

  Hereinafter, the process of estimating the subject distance based on the light field image will be described using a simplified model.

  For the sake of simplicity, it is assumed that four pixels are allocated to the light receiving region 4 for one microlens 3 and are squarely arranged with “2 × 2 pixels” vertically and horizontally.

At this time, a “2 × 2 array” of individual electric signals of “2 × 2 pixels” constituting one light receiving region 4 is called a macro pixel.
Since there is no possibility of confusion, the macro pixel constituting the light receiving region 4 is referred to as “macro pixel 4”.

There are the same number of macropixels 4 as there are microlenses 3.
Next, a “macro pixel group” is obtained from the set of macro pixels 4, and a plurality of “two-dimensional images for shift amount calculation” are extracted and created from the macro pixel group.

The left diagram of FIG. 2 illustrates the “micropixel group” in an explanatory manner.
The macro pixel group MPG is configured by arranging nine macro pixels in a square array of “3 × 3 array”. A portion of “2 × 2 pixels” surrounded by a thick line in the figure is a macro pixel.

  The macro pixel group MPG in this figure is configured by setting a specific macro pixel at the center and surrounding it with eight macro pixels.

Next, a plurality of “two-dimensional images for shift amount calculation” are extracted and created from the macro pixel group MPG. This two-dimensional image is obtained by “rearranging the arrangement of electric signals of each pixel”.
The right diagram in FIG. 2 shows an example of rearrangement.
That is, the two-dimensional image 40A is obtained by “rearranging” the “upper left pixel” of the nine micropixels constituting the macropixel group MPG according to the arrangement of the micropixels.

  The nine arrows in the upper diagram of FIG. 2 represent “pixel arrangement rules in rearrangement”.

In this case, the electrical signals of the light receiving elements at the upper left of each macro pixel are rearranged.
Similarly, the two-dimensional image 40B is obtained by “rearranging” the “upper right pixel” of the nine micropixels constituting the macropixel group MPG according to the arrangement of the micropixels.

  The nine arrows in the lower diagram of FIG. 2 represent “pixel arrangement rules in rearrangement”.

A plurality of such two-dimensional images are created.
For example, two-dimensional images 40A and 40B shown in FIG. 2 are obtained.

  FIG. 3 illustrates “two two-dimensional images” obtained by the above rearrangement.

  In these two-dimensional images, “person” is in the foreground and “tree” is in the background, but the “diopter” is large for the foreground person and the diopter for the background tree is small.

  Therefore, it can be seen from FIG. 3 that a person with a high diopter shifts “large” and a tree with a low diopter shifts “small” during rearrangement as described above.

To supplement a little, in the example described above, the number of pixels constituting the two-dimensional image is 9 pixels, which is a “3 × 3 array”.
When the macro pixel is composed of more pixels (for example, 10 × 10 pixels), the macro pixel may be extracted and rearranged one by one from the macro pixel.
Alternatively, a “total or average value” of a plurality of pixels (for example, 2 × 2 pixels) may be calculated and rearranged.
By “rearranging the sum or average value”, the ratio of noise to signal (SN ratio) can be increased.
In FIG. 2, for the sake of simplicity, the number of macro pixel groups is as very small as nine, and the number of pixels of the reconstructed two-dimensional images 40A and 40B is nine.

  This is for simplicity of explanation, and in fact, it is meaningful as an image by increasing the number of microlenses constituting the lens array.

Next, “a method for estimating a subject distance from a plurality of two-dimensional images created by rearrangement” will be described.
“Subject distance estimation” is calculated based on shift amounts between a plurality of two-dimensional images created by rearranging from different positions of macro pixels.

As described above, the two two-dimensional images shown in FIG. 3 are two two-dimensional images reconstructed from the nine macro pixels constituting the macro pixel group MPG of FIG.
The shift direction in this case is the horizontal direction, which is a two-dimensional image according to “rearrangement of upper left pixels” and “rearrangement of upper right pixels” of each macro pixel in FIG.

In the case of “rearrangement of upper left pixel and rearrangement of lower left pixel”, there is a shift in the vertical direction, and in the case of rearrangement of upper left pixel and rearrangement of the lower right pixel, “shift diagonally”. There is.
The shift amount between these two-dimensional images is obtained by pattern matching such as block matching to obtain the “number of pixels corresponding to the shift amount”. This is converted into distance.

In the description of the two-dimensional image shown in FIG. 3, as described above, the number of macro pixels is extremely simplified to “2 × 2 pixels” in order to simplify the description.
Therefore, the two-dimensional image shown in FIG. 4 is 9 pixels according to the above description, but of course, it is actually composed of “a much larger number of pixels”.

Various pattern matching methods (algorithms) have been conventionally known, and these known methods can be appropriately used to obtain the shift amount.
As an example, the case of image processing by “template matching” will be briefly described.

  In this description, it is assumed that the number of pixels of the two-dimensional image shown in FIG. 3 is about 500 × 500 pixels, for example.

  For example, in the case of estimating the subject distance with respect to “a person as a subject” based on the two two-dimensional images in FIG. 3, the shift amount of the person portion is obtained.

  In this case, for example, an “N × M pixel template” is set in the face portion of the person in the two-dimensional image in the left diagram of FIG. The two-dimensional image in the right diagram of FIG. 4 is a “target image”.

  At this time, the pixel value (electric signal value) at the template position (i, j) is “T (i, j)”, and the pixel value of the target image superimposed on the template is “I (i, j)”. "

  At this time, either “T (i, j) and I (i, j)” is used to calculate either of the following two expressions. Needless to say, the calculation device 6 performs this calculation.

R _SSD = ΣΣ {I (i, j) −T (i, j)} ² (Formula 1)
R _SAD = ΣΣ | I (i, j) −T (i, j) | (Formula 2)
The “double sum” in these equations is taken “from i = 0 to N−1 for i” and “j = 0 to M−1 for j”.

When the template and the target image match best, the values of Equation 1 and Equation 2 are the smallest.
From the value of “i” when the value of Equation 1 or Equation 2 is minimized, the “lateral shift amount” is obtained in units of pixels.
The shift amount and the subject distance are generally in an “inverse proportion” relationship, but the specific relationship depends on the specific specification of the distance measuring device.

  Specific specifications include the focal length and numerical aperture of the imaging lens 1, the arrangement density and focal length (reference value) of the microlenses in the lens array 2, the pixel density and the number of pixels of the imaging device 5, and the like.

  The “relationship between the shift amount and the subject distance” can be experimentally obtained in advance based on the specific specification and defined as a “look-up table” or an “estimation formula”.

  In the present invention, since the focal length of the microlens can be changed, the lookup table or the estimation formula is obtained for each of the plurality of focal lengths to be changed.

  For example, considering the case where the focal length of the microlens is long and short, the “relation between the shift amount and the subject distance” obtained for each case is shown in FIG.

  In FIG. 4, a curve 50 shows the relationship between “the shift amount between two-dimensional images created by macro pixels photographed using a lens array of a micro lens having a long focal length” and the subject distance.

  A curve 51 is a relationship between “the shift amount between two-dimensional images created by macro pixels photographed using a lens array of microlenses having a short focal length” and the subject distance.

The subject distance can be estimated by the solid line 50 from the shift amount between the two-dimensional images created from the “macropixel by the lens array of the micro lens having a long focal length”.
Further, the subject distance can be estimated by the dotted line 51 from the shift amount between the two-dimensional images created from the “macropixel by the lens array of the microlens having a short focal length”.

  Curves 51 and 52 in FIG. 4 also indicate that the shift amount and the subject distance are in an “inverse proportion” relationship.

Therefore, the estimation formula generally assumes that the subject distance is “d” and the shift amount (number of pixels) is “P”.
It becomes something like this.
K is a proportionality constant in the above “inverse proportion”, and is “K1” when the focal length is long, and “K2” when the focal length is short.
d = K1 / P (3)
For short focal lengths,
d = K2 / P (4)
It becomes.

For example, if the standard subject distance is 1000 mm, K1 = 5000, and K2 = 3000, the relationship between d and P is as follows according to the estimation formula (3) when the focal length is long:
d = 1000 P = 5
d = 1111 P = 4.5
d = 1250 P = 4
d = 1429 P = 3.5
d = 1667 P = 3
And so on.

Further, according to the estimation formula (4) when the focal length is short, the relationship between d and P is as follows:
d = 1000 P = 3
d = 1200 P = 2.5
d = 1500 P = 2
d = 2000 P = 1.5
d = 3000 P = 1
And so on.

  Therefore, these values can be classified by “focal length” and stored in the lookup table, and the subject distance: d can be searched according to the obtained shift amount: P.

  Alternatively, the estimation formula (3) or (4) is selected depending on the magnitude of the focal length, and the subject distance: d can be calculated according to the obtained shift amount: P.

  Two patterns are conceivable for adjusting the focal length of the microlens when measuring the subject distance.

The first is a case where the subject distance to be measured is “known to some extent” in advance.
In this case, the measurer adjusts the “focal length of the microlens” according to the subject distance to be measured, measures the distance, and resets the “more suitable focal length” according to the result.

  Then, the distance measurement is repeated. This process can be repeated as necessary, and the accuracy of measurement improves each time it is repeated.

  The “reset of focal length” may be performed by the measurer, but may be set to a more suitable focal length by controlling the estimated subject distance by feedback.

  That is, the distance measuring device can have a function of resetting the focal length by the feedback.

  The second is a case where the subject distance is unknown. At this time, a lens array having a plurality of focal lengths is set and distance measurement is performed. As a result, the subject distance is determined.

  When measuring with higher spatial resolution, the measured subject distance is fed back, adjusted to a focal length corresponding to the subject distance, and the measurement is repeated.

  Also in this case, the distance measuring device can have a “focal length resetting function by feedback”.

The flow of processing in the first case is shown in FIG.
The approximate value of the subject distance to be measured is known.

  Step: In “S1”, the “focal length of the electrowetting lens” is controlled. With this control, a focal length suitable for the “approximately known subject distance” is set.

  Step: In S2, “line field image” is acquired as described above.

Step: In S3, “a plurality of two-dimensional images” are created from the macro pixel group.
Step: In S4, “calculate the shift amount between a plurality of two-dimensional images”.

  Step: In S5, “estimate the subject distance corresponding to the calculated shift amount”.

  Thereafter, the process from the resetting of the focal length to the estimation of the subject distance can be repeated as necessary.

The second case will be described below.
In this case, since the subject distance as the measurement target is “not known in advance”, the measurement is performed by the following method.
The microlenses 3 constituting the lens array 2 can be changed in focal length by an electrowetting lens, but the focal length can be changed in units of microlenses.

Therefore, the lens array 2 is “mixed with microlenses having different focal lengths”.
For the sake of simplicity, a description will be given of a case where “a lens having a long focal length” and “a lens having a short focal length” are mixed in a checkered pattern.

The state shown in FIG. 6A is a state at the start of measurement, and “a microlens 3 with a short focal length” and “a microlens 8 with a long focal length” are arranged in a checkered pattern.
FIG. 7 shows a macro pixel group 10 in a “3 × 3 array” of nine micro pixels centering on a macro pixel immediately below the micro lens 3 with a short focal length.
The macro pixels are surrounded by a thick line, and each macro pixel is composed of “2 × 2” light receiving elements.
The “white macropixel” is a macropixel immediately below the microlens 3 having a short focal length.
The “gray macro pixel” is a macro pixel immediately below the microlens 8 having a long focal length.
In order to estimate subject distances corresponding to the length and shortness of the focal length, the two-dimensional images 11 and 12 are created by rearranging the electrical signals of the pixels of the respective macro pixels.

The rearrangement method is indicated by arrows in the figure. Pixels at the same position (upper left in the case of FIG. 6) of each macro pixel are rearranged according to the arrangement of the macro pixels.
The “portion 13 having no electrical signal to be rearranged” can be obtained by “interpolating from the values of surrounding electrical signals”.
The rearrangement of the pixels at “positions other than the upper left” of the macro pixels is the same, and in the case of FIG. 7, the macro pixels are composed of 2 × 2 pixels.
Therefore, “four two-dimensional images” can be created from the macropixels immediately below the microlenses with a short focal length and the macropixels immediately below the microlenses with a long focal length.

The method for estimating the subject distance from the two-dimensional image created from the macro pixels photographed by the microlenses having different focal lengths is the same as described above.
That is, the subject distance for each focal length is estimated using the relationship between the shift amount corresponding to the focal length and the subject distance (preliminarily obtained as an estimation formula or a lookup table).

  As described above, microlenses having different focal lengths are simultaneously present in the same lens array, thereby enabling “preferable measurement for a wide subject distance by one photographing”.

  FIG. 8 shows the flow of processing.

Step: “Set the lens array to have a plurality of focal lengths” in S21.
That is, an array in which microlenses having a long focal length and microlenses having a short focal length are two-dimensionally mixed is set in the lens array.

Step: “Acquire light field image” in S21.
Step: In S23, “create a two-dimensional image from each macropixel group that receives light rays that have passed through microlenses having different focal lengths”.

  This portion is as described with reference to FIG.

Step: “Calculate the shift amount included in the two-dimensional image” in S24.
Step: In S25, “estimate the subject distance from the shift amount using an appropriate shift-distance relationship”.

  Step: “Subject distance: d” is obtained in S26.

  Step: In S27, “set a focal length suitable for higher-accuracy measurement of the subject distance d thus obtained”.

  FIG. 6B shows this state, and the microlenses 3 of the lens array 2 are all set to the same focal length.

  Thereafter, the “light field image” is captured at the reset focal length, the macro pixel group is obtained, and the “two-dimensional image” is created from this in step S28.

Step: “Send out the shift amount included in the two-dimensional image” in S29.
Step: In S30, “estimate subject distance based on shift amount”.

  In this way, an appropriate distance measurement can be performed even for a subject distance that is not known in advance, and a suitable distance estimation can be performed even when the subject distance differs greatly.

  In this case, the “reset of focal length” may be performed by the measurer, but it may be automatically set to a more suitable focal length by feeding back and controlling the estimated subject distance.

  FIG. 9 is a block diagram illustrating an example of the configuration of the arithmetic device.

  An image taken into the image sensor 5 from the imaging lens 1 via the lens array 2 is output as an electrical signal and converted into digital image data by the A / D converter 51.

The timing signal generator 55 generates a timing signal for operating the image sensor 5 and the A / D converter 51 based on an instruction from the CPU 56.
The image processing circuit 53 temporarily stores the image data, and performs preprocessing such as noise removal on the image data to obtain a light field image.
The ROM 59 stores “a program for causing the device to function as a distance measuring device”.
The CPU 56 executes the program stored in the ROM 59 using “RAM 57 as a work area”, thereby causing the device to function as a distance measuring device.
The processed data is recorded in the memory 58. The operation unit 60 includes a switch, a lever, a touch panel, and the like. The processing result is displayed on the LCD 52.

  The driver 61 changes the focal length of the microlenses 3 of the lens array 2 based on an instruction from the CPU 56.

  “Signal exchange” in each unit is performed via the bus 70.

1 Imaging lens
2 Lens array
3 Microlens
4 macro pixels
5 Image sensor
6 Arithmetic unit

JP 2009-229125 A

Adelson and Wang `` Single Lens Stereo with a Plenoptic Camera '', IEEE Transactions on pattern analysis and machine intelligence, vol. 14, No. 2, February 1992. Christian Perwas and Lennart Wietzke `` Single lens 3D-camera with extended depth-of-field ''

Claims (10)

An imaging lens for entering object light from a subject;
A lens array into which object light transmitted through the imaging lens is incident;
An image sensor that receives light passing through the lens array and outputs image information;
An arithmetic unit for estimating the distance to the subject,
The lens array is a two-dimensional array of microlenses that can vary the focal length,
The imaging element has a plurality of light receiving elements corresponding to each of the microlenses,
The distance measuring device, wherein the computing device performs the distance estimation based on the image information. The distance measuring device according to claim 1,
A distance measuring device characterized in that the focal length of a microlens in a lens array can be changed individually or in groups of a plurality of microlenses. The distance measuring device according to claim 1 or 2,
A distance measuring device that changes a focal length of a microlens in a lens array based on a result of distance estimation. In the distance measuring device according to any one of claims 1 to 3,
At the start of distance measurement, a microlens having a different focal length is mixed in the lens array, and after the distance measurement, the focal length of the microlens is changed according to an estimation result. In the distance measuring device according to any one of claims 1 to 4,
A distance measuring device characterized in that an electrowetting lens is used as a microlens capable of changing a focal length. In the distance measuring device according to any one of claims 1 to 5,
A computing device that performs distance estimation corresponding to the focal length extracts and creates a plurality of two-dimensional images for calculating the shift amount based on the image of the macro pixel group on the basis of the captured image of the image sensor. A function for calculating the shift amount of
A function of estimating a distance based on the calculated shift amount by referring to a lookup table predetermined for each of a plurality of focal lengths for a correspondence relationship between the shift amount and the imaging distance. apparatus. The distance measuring device according to any one of claims 1 to 6,
A computing device that performs distance estimation corresponding to the focal length extracts and creates a plurality of two-dimensional images for calculating the shift amount based on the image of the macro pixel group on the basis of the captured image of the image sensor. A function for calculating the shift amount of
A distance measuring device having a function of estimating a distance based on the calculated shift amount with reference to an estimation formula predetermined for each of a plurality of focal lengths for a correspondence relationship between the shift amount and the imaging distance . A distance measuring method using the distance measuring device according to claim 1,
A macro pixel is obtained from the output of a plurality of light receiving elements corresponding to each microlens, and a plurality of two-dimensional images for calculating the shift amount are extracted and created from a macro pixel group constituted by the macro pixel and surrounding macro pixels. And a process of
Calculating shift amounts of a plurality of two-dimensional images extracted and created by pattern matching;
A distance measuring method comprising a step of estimating an imaging distance based on a predetermined relationship between a shift amount and an imaging distance according to a focal length of the microlens. The distance measuring method according to claim 8, wherein
A distance measuring method characterized in that the focal length of a microlens is set to a desired value and image information of a subject is captured. The distance measuring method according to claim 8 or 9,
A distance measuring method, wherein the focal length of the microlens is changed based on the estimated subject distance, and image information of the subject is captured again.

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