Distance measurement apparatus and distance measurement method

Patent metadata

Field	Value
Publication number	US-9467616-B2
Application number	US-201414407569-A
Country	US
Kind code	B2
Filing date	Feb 26, 2014
Priority date	Apr 15, 2013
Publication date	Oct 11, 2016
Grant date	Oct 11, 2016

Abstract

A distance measurement apparatus includes: an imaging element that images an object by performing exposure and readout of electric charges sequentially for each row or column; an optical system that has a controllable in-focus position; an imaging control unit that moves the in-focus position at constant speed, and causes the imaging element to image the object sequentially while the in-focus position is being moved, to obtain blurred images; a distance measurement unit that measures a distance from a reference position in the optical system to the object using the blurred images and a point spread function dependent on object distance; and a correction unit that performs a correction process on the distance for each row or column according to a movement range of the in-focus position in which the in-focus position is moved during the exposure for each row or column when the blurred images are obtained.

First claim

The invention claimed is:

1. A distance measurement apparatus comprising:
an imaging element that includes photoelectric conversion elements arranged in rows and columns, and images an object by performing exposure and readout of electric charges sequentially for each of the rows or each of the columns;
an optical system that is for forming an image of the object on the imaging element and has an in-focus position that is controllable;
control circuitry; and
a storage device, the control circuitry being operative to:
(i) control the optical system to cause the in-focus position to move at constant speed and (ii) cause the imaging element to image the object sequentially while the in-focus position is being moved at the constant speed, to obtain a plurality of blurred images;
measure a distance from a reference position in the optical system to the object using the plurality of blurred images and a point spread function dependent on object distance; and
perform, before or after the measurement of the distance, a correction process on the distance for each of the rows or each of the columns according to a movement range of the in-focus position in which the in-focus position is moved during the exposure for the each of the rows or the each of the columns when the plurality of blurred images are obtained.

2. The distance measurement apparatus according to claim 1 ,
wherein the control circuitry is operative:
obtain, as the plurality of blurred images, at least (n+1) blurred images where n is an integer greater than or equal to 1;
when a point in time for starting exposure of the imaging element to obtain a first image which is one of the at least (n+1) blurred images that is obtained first is denoted by TS(1), a point in time for ending the exposure of the imaging element to obtain the first image is denoted by TE(1), a point in time for starting exposure of the imaging element to obtain a second image which is one of the at least (n+1) blurred images that is obtained last is denoted by TS(1+n), and a point in time for ending the exposure of the imaging element to obtain the second image is denoted by TE(1+n),
(i) cause the in-focus position to be at a first position at TS(1);
(ii) cause the in-focus position to be at a second position at TE(1+n), the second position being different from the first position;
(iii) cause the in-focus position to move at the constant speed in a period from TS(1) to TE(1) and in a period from TS(1+n) to TE(1+n);
measure the distance from the reference position to the object for each pixel in at least one of the first image or the second image using the point spread function, the first image, and the second image; and
perform the correction process according to a movement range of the in-focus position in which the in-focus position is moved during the exposure for the each of the rows or the each of the columns when the first image and the second image are obtained.

3. The distance measurement apparatus according to claim 2 ,
wherein the control circuitry is operative to cause the in-focus position to move, in the period from TS(1+n) to TE(1+n), at a speed equal to a speed at which the in-focus position moves in the period from TS(1) to TE(1).

4. The distance measurement apparatus according to claim 3 ,
wherein the control circuitry is operative to, before the obtainment of the plurality of blurred images, determine whether or not a condition that the point in time for starting the exposure of the imaging element to obtain the second image is earlier than the point in time for ending the exposure of the imaging element to obtain the first image is satisfied, and
upon determining that the condition is satisfied (i) perform a process to obtain the plurality of blurred images, (ii) perform a process to measure the distance, and (iii) perform the correction process.

5. The distance measurement apparatus according to claim 4 ,
wherein the control circuitry is operative to obtain, as the plurality of blurred images, at least (n+1) blurred images where n is an integer greater than or equal to 1, and
when a point in time for starting exposure of the imaging element to obtain a (1+x)-th image which is one of the plurality of blurred images is denoted by TS(1+x), a point in time for ending the exposure of the imaging element to obtain the (1+x)-th image is denoted by TE(1+x), a point in time for starting exposure of the imaging element to obtain a (1+x+1)-th image which is one of the plurality of blurred images is denoted by TS(1+x+1), and a point in time for ending the exposure of the imaging element to obtain the (1+x+1)-th image is denoted by TE(1+x+1) where (n−1)≧x≧0,
the control circuitry is operative to determine a sequence of points in time TE(1+x) and TS(1+x+1), and
cause the in-focus position to move at the constant speed from a third position to a fourth position in a period from TS(1+x) to TE(1+x+1) upon determining that TE(1+x)>TS(1+x+1) holds, the fourth position being different from the third position.

6. The distance measurement apparatus according to claim 5 ,
wherein upon determining that TE(1+x)<TS(1+x+1) holds,
the control circuitry is operative to:
(i) cause the in-focus position to stop at the third position in a period from TS(1+x) to TE(1+x);
(ii) cause the in-focus position to move from the third position to the fourth position in a period from TE(1+x) to TS(1+x+1); and
(iii) cause the in-focus position to stop at the fourth position in a period from TS(1+x+1) to TE(1+x+1).

7. The distance measurement apparatus according to claim 2 ,
wherein n is 1.

8. The distance measurement apparatus according to claim 2 ,
wherein n is an integer greater than or equal to 2, and
the control circuitry is operative to measure the distance using three or more blurred images as the plurality of blurred images.

9. The distance measurement apparatus according to claim 1 ,
wherein the control circuitry is operative to calculate, for each of the rows or each of the columns in the imaging element, an amount of correction for the distance measured, and
the control circuitry is operative to calculate the amount of correction for each of the rows or each of the columns in the imaging element, to approximate (i) a diameter of the point spread function corresponding to the movement range of the in-focus position in which the in-focus position is moved during the exposure for the each of the rows or the each of the columns in the imaging element and (ii) a diameter of a point spread function corresponding to a range of an in-focus position of light that has traveled a predetermined distance.

10. The distance measurement apparatus according to claim 9 ,
wherein the control circuitry is operative to, after the measurement of the distance, perform the correction process by adding or subtracting the amount of correction calculated for each of the rows or each of the columns in the imaging element to or from the distance measured.

11. The distance measurement apparatus according to claim 9 ,
wherein the control circuitry is operative to, before the measurement of the distance, perform the correction process by changing the point spread function that is to be used to calculate the distance, according to the amount of correction calculated for each of the rows or each of the columns in the imaging element, and
the control circuitry is operative to measure the distance using the point spread function that is obtained after the correction process is performed.

12. The distance measurement apparatus according to claim 1 ,
wherein the control circuitry is operative to cause a part of the imaging element including photoelectric

Assignees

• Panasonic Ip Man Co Ltd

Inventors

• Yasugi Shunsuke
• Ezawa Kozo
• Kawamura Takashi

Classifications

• G01C3/32 Primary

  by focusing the object, e.g. on a ground glass screen · CPC title

• H04N23/959 Primary

  by adjusting depth of field during image capture, e.g. maximising or setting range based on scene characteristics · CPC title

• H04N5/23212 Primary

  Electricity · mapped topic

• G02B7/36

  using image sharpness techniques {, e.g. image processing techniques for generating autofocus signals (image data processing per se G06T; in cameras having a solid state image sensor H04N23/67)} · CPC title

• H04N5/353

  Electricity · mapped topic