Solid object detection device and solid object detection method

1. A solid object detection device comprising:

a processor that

transforms a first photographed image and a second photographed image which are photographed by a camera at different timings in travel of a vehicle into a first overhead view image and a second overhead view image, respectively;

generates a subtracted image between the first overhead view image and the second overhead view image whose photographing positions are aligned with each other;

specifies a position of a solid object present around the vehicle based on the subtracted image; and

generates a masked subtracted image in which a region other than a solid object candidate region where the solid object appears is masked in the subtracted image is masked, wherein

the processor

specifies a position of the solid object in the subtracted image based on the masked subtracted image,

specifies a near grounding line of the solid object in the subtracted image based on a position on a horizontal axis in which a travel direction difference amount accumulation value exceeds a third threshold value in a masked difference histogram, which has a horizontal direction orthogonal to a travel direction of the vehicle as a horizontal axis and has the travel direction difference amount accumulation value resulting from accumulation of a pixel value of each pixel of the masked subtracted image along the travel direction as a vertical axis, and

specifies the position of the solid object in the subtracted image based on the near grounding line specified.

2. The solid object detection device according to claim 1 , wherein the processor

specifies a closest range to the photographing position in a range in which the travel direction difference amount accumulation value successively exceeds the third threshold value on the horizontal axis of the masked difference histogram and specifies a spot in immediate front of the range, as seen from the photographing position, as a position of the near grounding line.

3. The solid object detection device according to claim 2 , wherein processor

specifies a far grounding line of the solid object in the subtracted image based on a width of the solid object and the near grounding line.

4. The solid object detection device according to claim 3 , wherein

the processor

specifies a first region in which the solid object is positioned in the near grounding line and a second region in which the solid object is positioned in the far grounding line based on an intersection point between a radial line which extends from the photographing position in the subtracted image and includes a perpendicular direction contour line of the solid object and each of the near grounding line and the far grounding line and that specifies a solid object region in which the solid object appears in the subtracted image based on a range in which the first region and the second region overlap with each other.

5. The solid object detection device according to claim 4 , wherein

the processor

specifies a radial line whose radial line direction difference amount accumulation value is a fourth threshold value or greater in a difference histogram, which has each of plural radial lines extending from the photographing position in the subtracted image as a horizontal axis and has the radial line direction difference amount accumulation value resulting from accumulation of each pixel value of the subtracted image along the radial line as a vertical axis, as the radial line which includes the perpendicular direction contour line of the solid object.

6. The solid object detection device according to claim 4 , wherein

the processor

specifies a radial line whose radial line direction edge intensity accumulation value is a fifth threshold value or greater in an edge intensity histogram, which has each of plural radial lines extending from the photographing position in an edge image which extracts a contour component of the solid object from an image corresponding to a photographed image being photographed latest between the first overhead view image and the second overhead view image as a horizontal axis and has the radial line direction edge intensity accumulation value resulting from accumulation of each pixel value of the edge image along the radial line as a vertical axis, as the radial line which includes the perpendicular direction contour line of the solid object.

7. The solid object detection device according to claim 4 , wherein

the processor

obtains the radial line based on the subtracted image in which a region other than a region interposed between the near grounding line and the far grounding line is masked, specifies the first region based on an intersection point between the radial line and the near grounding line,

obtains the radial line based on the subtracted image in which a region other than a far region which is farther than the near grounding line when seen from the photographing position is masked, and specifies the second region based on an intersection point between the radial line and the far grounding line.

8. The solid object detection device according to claim 1 , wherein

the processor

specifies a radial line whose radial line direction edge intensity accumulation value is a second threshold value or smaller in an edge intensity histogram, which has each of plural radial lines extending from the photographing position in an edge image which extracts a contour component of the solid object from an image corresponding to a photographed image being photographed latest between the first overhead view image and the second overhead view image as a horizontal axis and has the radial line direction edge intensity accumulation value resulting from accumulation of each pixel value of the edge image along the radial line as a vertical axis, and masks a region that corresponds to the radial line in the subtracted image.

9. A solid object detection device comprising:

a processor that

transforms a first photographed image and a second photographed image which are photographed by a camera at different timings in travel of a vehicle into a first overhead view image and a second overhead view image, respectively;

generates a subtracted image between the first overhead view image and the second overhead view image whose photographing positions are aligned with each other;

specifies a position of a solid object present around the vehicle based on the subtracted image; and

generates a masked subtracted image in which a region other than a solid object candidate region where the solid object appears is masked in the subtracted image, wherein

the processor

specifies a position of the solid object in the subtracted image based on the masked subtracted image, and

specifies a radial line whose radial line direction difference amount accumulation value is a first threshold value or smaller in a difference histogram, which has each of plural radial lines extending from the photographing position in the subtracted image as a horizontal axis and has the radial line direction difference amount accumulation value resulting from accumulation of each pixel value of the subtracted image along the radial line as a vertical axis, and masks a region that corresponds to the radial line in the subtracted image.

10. A solid object detection method comprising:

a first step of transforming a first photographed image and a second photographed image which are photographed by a camera at different timings in travel of a vehicle into a first overhead view image and a second overhead view image, respectively;

a second step of generating a subtracted image between the first overhead view image and the second overhead view image whose photographing positions are aligned with each other;

a third step of generating a masked subtracted image in which a region other than a solid object candidate region where a solid object appears is masked in the subtracted image; and

a fourth step of specifying a position of the solid object in the subtracted image based on the masked subtracted image, wherein

the fourth step includes

specifying a near grounding line of the solid object in the subtracted image based on a position on a horizontal axis in which a travel direction difference amount accumulation value exceeds a third threshold value in a masked difference histogram, which has a horizontal direction orthogonal to a travel direction of the vehicle as a horizontal axis and has the travel direction difference amount accumulation value resulting from accumulation of a pixel value of each pixel of the masked subtracted image along the travel direction as a vertical axis, and

specifying the position of the solid object in the subtracted image based on the near grounding line specified.