Distance measurement apparatus, distance measurement method, and non-transitory computer-readable storage medium

1. An apparatus for distance measurement, the apparatus comprising:

a memory; and

a processor coupled to the memory and configured to

execute a measurement process that includes generating an image having a plurality of pixels, each of the plurality of pixels corresponding to a range point and representing a distance value obtained by measuring a distance to the range point based on reflected light of a pulsed laser beam for two-dimensional scanning,

execute a first process that includes extracting, from the image, a first area having a plurality of range points at which the distance value is less than or equal to a first threshold, wherein a difference between each pair of the plurality of range points included in the first area is less than or equal to a second threshold, and the first area has an area size less than or equal to a threshold size, and

execute a second process that includes

extracting an area group which has a plurality of the first areas, wherein a distance, in terms of two-dimensional coordinates in the image, between each of the plurality of the first areas and another of the plurality of the first areas is less than or equal to a third threshold, and a difference of the distance value between each pair of the plurality of the first areas is greater than a fourth threshold, and

determining the area group as a noise area when the number of the plurality of the first areas included in the area group is greater than or equal to a certain number.

2. The apparatus according to claim 1 ,

wherein the first process includes

extracting the first area by grouping range points, each of which has a distance value on the image, the distance value being less than or equal to the first threshold, with the difference between the distance values of the range points being less than or equal to the second threshold, and

extracting, among plural ones of the first area extracted, the first area the area size of which is less than or equal to the threshold size, and

wherein the second process includes

extracting the area group formed by grouping the first areas, each of which has a distance in terms of the two-dimensional coordinates in the image, the distance being less than or equal to the third threshold, with the difference between the distance values being greater than the fourth threshold, and

determining, as the noise area, an area group where the number of the first areas forming the area group is greater than or equal to a certain number.

3. The apparatus according to claim 1 ,

wherein the processor is configured to

execute a third process that includes extracting, among the first areas determined as the noise area, a second area of range points having a difference between the distance values, the difference being less than or equal to a threshold, the threshold being greater than the second threshold, and

execute a fourth process that includes determining, as a noise area, among the first areas determined as the noise area, a portion where the first areas in the second area extracted in the third process, the second area having an area less than or equal to a certain amount, overlap the area group determined as the noise area in the second process.

4. The apparatus according to claim 1 ,

wherein the processor is configured to

execute a removal process that includes removing the area group determined as the noise area from the image.

5. The apparatus according to claim 1 ,

wherein one range point in terms of the two-dimensional coordinates in the image corresponds to one or a plurality of pixels of the image.

6. The apparatus according to claim 1 ,

wherein the processor is configured to execute a generation process that includes generating an image representing each range point by pixel color in accordance with a distance value.

7. The apparatus according to claim 1 , the apparatus further comprising:

a light-transmitting circuit configured to transmit a pulsed infrared or near-infrared laser beam for two-dimensional scanning; and

a light-receiving circuit configured to detect reflected light of the laser beam and measures a distance to each range point.

8. A method, implemented by a processor circuitry, for distance measurement, the method comprising:

executing, by the processor circuitry, a measurement process that includes generating an image having a plurality of pixels, each of the plurality of pixels corresponding to a range point and representing a distance value obtained by measuring a distance to the range point based on reflected light of a pulsed laser beam for two-dimensional scanning;

executing, by the processor circuitry, a first process that includes extracting, from the image, a first area having a plurality of range points at which the distance value is less than or equal to a first threshold, wherein a difference between each pair of the plurality of range points included in the first area is less than or equal to a second threshold, and the first area has an area size less than or equal to a threshold size; and

executing, by the processor circuitry, a second process that includes

extracting an area group which has a plurality of the first areas, wherein a distance, in terms of two-dimensional coordinates in the image, between each of the plurality of the first areas and another of the plurality of the first areas is less than or equal to a third threshold, and a difference of the distance value between each pair of the plurality of the first areas is greater than a fourth threshold, and

determining the area group as a noise area when the number of the plurality of the first areas included in the area group is greater than or equal to a certain number.

9. The method according to claim 8 ,

wherein the first process includes

extracting the first area by grouping range points, each of which has a distance value on the image, the distance value being less than or equal to the first threshold, with the difference between the distance values of the range points being less than or equal to the second threshold, and

extracting, among plural ones of the first area extracted, the first area the area size of which is less than or equal to the threshold size, and

wherein the second process includes

extracting the area group formed by grouping the first areas, each of which has a distance in terms of the two-dimensional coordinates in the image, the distance being less than or equal to the third threshold, with the difference between the distance values being greater than the fourth threshold, and

determining, as the noise area, an area group where the number of the first areas forming the area group is greater than or equal to a certain number.

10. The method according to claim 8 , the method further comprising:

executing, by the processor circuitry, a third process that includes extracting, among the first areas determined as the noise area, a second area of range points having a difference between the distance values, the difference being less than or equal to a threshold, the threshold being greater than the second threshold, and

executing, by the processor circuitry, a fourth process that includes determining, as a noise area, among the first areas determined as the noise area, a portion where the first areas in the second area extracted, the second area having an area less than or equal to a certain amount, overlap the area group determined as the noise area in the determining.

11. The method according to claim 8 , the method further comprising:

executing, by the processor circuitry, a removal process that includes removing the area group determined as the noise area from the image.

12. The method according to claim 8 ,

wherein one range point in terms of the two-dimensional coordinates in the image corresponds to one or a plurality of pixels of the image.

13. The method according to claim 8 , the method further comprising:

executing, by the processor circuitry, a generation process that includes generating an image representing each range point by pixel color in accordance with a distance value.

14. A non-transitory computer-readable storage medium storing a program that causes processor circuitry to execute a distance measurement process, the distance measurement process comprising:

executing a measurement process that includes generating an image having a plurality of pixels, each of the plurality of pixels corresponding to a range point and representing a distance value obtained by measuring a distance to the range point based on reflected light of a pulsed laser beam for two-dimensional scanning;

executing a first process that includes extracting, from the image, a first area having a plurality of range points at which the distance value is less than or equal to a first threshold, wherein a difference between each pair of the plurality of range points included in the first area is less than or equal to a second threshold, and the first area has an area size less than or equal to a threshold size; and

executing a second process that includes

extracting an area group which has a plurality of the first areas, wherein a distance, in terms of two-dimensional coordinates in the image, between each of the plurality of the first areas and another of the plurality of the first areas is less than or equal to a third threshold, and a difference of the distance value between each pair of the plurality of the first areas is greater than a fourth threshold, and

determining the area group as a noise area when the number of the plurality of the first areas included in the area group is greater than or equal to a certain number.

15. The storage medium according to claim 14 ,

wherein the first process includes

extracting the first area by grouping range points, each of which has a distance value on the image, the distance value being less than or equal to the first threshold, with the difference between the distance values of the range points being less than or equal to the second threshold, and

extracting, among plural ones of the first area extracted, the first area the area size of which is less than or equal to the threshold size, and

wherein the second process includes

extracting the area group formed by grouping the first areas, each of which has a distance in terms of the two-dimensional coordinates in the image, the distance being less than or equal to the third threshold, with the difference between the distance values being greater than the fourth threshold, and

determining, as the noise area, an area group where the number of the first areas forming the area group is greater than or equal to a certain number.

16. The storage medium according to claim 14 ,

wherein the distance measurement process includes

executing a third process that includes extracting, among the first areas determined as the noise area, a second area of range points having a difference between the distance values, the difference being less than or equal to a threshold, the threshold being greater than the second threshold, and

executing a fourth process that includes determining, as a noise area, among the first areas determined as the noise area, a portion where the first areas in the second area extracted, the second area having an area less than or equal to a certain amount, overlap the area group determined as the noise area in the determining.

17. The storage medium according to claim 14 ,

wherein the distance measurement process includes

executing a removal process that includes removing the area group determined as the noise area from the image.

18. The storage medium according to claim 14 ,

wherein one range point in terms of the two-dimensional coordinates in the image corresponds to one or a plurality of pixels of the image.

19. The storage medium according to claim 14 ,

wherein the distance measurement process includes

executing a generation process that includes generating an image representing each range point by pixel color in accordance with a distance value.