Visibility range measuring apparatus for vehicle and vehicle drive assist system

Abstract

A visibility range measuring apparatus for a vehicle includes an image capturing device, an image computing device, and a visibility range calculating device. The image capturing device captures first and second images of a road, each of which includes a target roadside object, from the vehicle at first and second image taking points, respectively, along the road at a time of driving the vehicle along the road. The image computing device computes an image feature of the captured target roadside object in the first image and an image feature of the captured target roadside object in the second image. The visibility range calculating device calculates a visibility range from the vehicle based on the image features of the captured target roadside object in the first and second images, and a distance between the first and second image taking points.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic view illustrating overall construction of a visibility range measuring apparatus for a vehicle according to an embodiment of the present invention;

FIG. 2 is a schematic view illustrating a state, where front images that fall within an image capturing range, which is set to include a roadside object while a vehicle is running, are repeatedly taken;

FIG. 3 is a block diagram showing a configuration of an image processor of the visibility range measuring apparatus;

FIG. 4A is an illustrative view showing a distant image that is taken when a roadside object is located at a large distance from a vehicle;

FIG. 4B is an illustrative view showing a near image that is taken when the roadside object, which is shown in the distant image, is located adjacent to the vehicle;

FIG. 5 is a schematic diagram that shows a relationship between a forward distance to a roadside object and edge intensity of a front image that captures the roadside object when the front image is taken from a vehicle;

FIG. 6 is a schematic diagram that shows a visibility range conversion table to calculate a visibility range from a relationship between an edge intensity difference and a travel distance of a vehicle;

FIG. 7 is a flowchart showing a flow of an operation of an image processor in the visibility range measuring apparatus;

FIG. 8 is a schematic diagram that shows a relationship between an edge intensity difference and a travel distance of a vehicle when a margin is allowed for the edge intensity difference, which corresponds to the travel distance of the vehicle, according to a first modification of the embodiment; and

FIG. 9 is a schematic diagram that shows a conversion table to calculate a visibility range from a relationship between a frequency component value difference and a travel distance of a vehicle, according to a second modification of the embodiment.

Claims

1. A visibility range measuring apparatus for a vehicle, comprising: image capturing means for capturing first and second images of a road, each of which includes a target roadside object, from the vehicle at first and second image taking points, respectively, along the road at a time of driving the vehicle along the road;image computing means for computing an image feature of the captured target roadside object in the first image and an image feature of the captured target roadside object in the second image; andvisibility range calculating means for calculating a visibility range from the vehicle based on: the image feature of the captured target roadside object in the first image;the image feature of the captured target roadside object in the second image; anda distance between the first taking point and the second image taking point on the road.

2. The visibility range measuring apparatus according to claim 1, further comprising subject image area setting means for setting a first subject image area in the first image and a second subject image area in the second image, wherein: the first subject image area and the second subject image area include the captured target roadside object and are generally homothetic to each other; andthe image computing means computes the image feature of the captured target roadside object in the first subject image area in the first image and the image feature of the captured target roadside object in the second subject image area in the second image.

3. The visibility range measuring apparatus according to claim 2, wherein: the first image taking point is located at a first distance from the target roadside object along the road;the second image taking point is located at a second distance from the target roadside object along the road, wherein the second distance is smaller than the first distance; andthe subject image area setting means sets the first subject image area in the first image first, and then sets the second subject image area in the second image based on: a position of the first subject image area in the first image; anda distance between the first image taking point and the second image taking point.

4. The visibility range measuring apparatus according to claim 2, wherein: the first image taking point is located at a first distance from the target roadside object along the road;the second image taking point is located at a second distance from the target roadside object along the road, wherein the second distance is smaller than the first distance; andthe subject image area setting means sets the second subject image area in the second image first, and then sets the first subject image area in the first image based on: a position of the second subject image area in the second image; anda distance between the first image taking point and the second image taking point.

5. The visibility range measuring apparatus according to claim 1, wherein: the image computing means computes an edge intensity of the captured target roadside object as the image feature; andthe visibility range calculating means calculates the visibility range based on an edge intensity difference between the edge intensity of the captured target roadside object in the first image and the edge intensity of the captured target roadside object in the second image.

6. The visibility range measuring apparatus according to claim 5, further comprising conversion table storing means for storing a conversion table, wherein: the visibility range is obtained by the visibility range calculating means from the conversion table, based on: the distance between the first image taking point and the second image taking point; andone of the edge intensity difference and the frequency component difference; andthe visibility range calculating means calculates the visibility range using the conversion table.

7. The visibility range measuring apparatus according to claim 1, wherein: the image computing means computes a frequency component of the captured target roadside object as the image feature; andthe visibility range calculating means calculates the visibility range based on a frequency component difference between the frequency component of the captured target roadside object in the first image and the frequency component of the captured target roadside object in the second image.

8. The visibility range measuring apparatus according to claim 7, further comprising conversion table storing means for storing a conversion table, wherein: the visibility range is obtained by the visibility range calculating means from the conversion table, based on: the distance between the first image taking point and the second image taking point; andone of the edge intensity difference and the frequency component difference; andthe visibility range calculating means calculates the visibility range using the conversion table.

9. The visibility range measuring apparatus according to claim 1, wherein the distance between the first image taking point and the second image taking point is obtained from a travel distance, which is traveled by the vehicle between the first and second image taking points.

10. The visibility range measuring apparatus according to claim 9, further comprising conversion table storing means for storing a conversion table, wherein: the visibility range is obtained by the visibility range calculating means from the conversion table, based on: the distance between the first image taking point and the second image taking point; andone of the edge intensity difference and the frequency component difference; andthe visibility range calculating means calculates the visibility range using the conversion table.

11. A vehicle drive assist system comprising: the visibility range measuring apparatus recited in claim 1; anddrive assisting means for assisting a driver of the vehicle with a drive operation of the vehicle using the visibility range, which is measured by the visibility range measuring apparatus.

12. A vehicle drive assist system comprising: the visibility range measuring apparatus recited in claim 1; andfront information providing means for providing information about a state ahead of the vehicle to a driver of the vehicle using the visibility range, which is measured by the visibility range measuring apparatus.

13. The vehicle drive assist system according to claim 12, wherein the front information providing means includes an information supply timing changing means for changing a timing, with which the information is provided to the driver of the vehicle, based on the visibility range.