JP2015087267A - Object detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an object detection device capable of stably extracting a synchronous detection region regardless of an intensity variation of disturbance light.SOLUTION: An object detection device includes: a luminance detection part 7 for detecting a luminance value of each pixel in the irradiation range of a light projection part 1 from an image-capture image of an imaging part 2; and an offset circuit 22 for setting a luminance output characteristic representing a relationship between an optical input and a luminance output in a region between a low region and a high region of the luminance output value for an optical input of the imaging part 2 on coordinates with an optical input and the luminance output as coordinate axes, and for changing a position of an optical input axial direction while maintaining an inclination of the luminance output characteristic in accordance with the luminance value of each pixel in the irradiation range.

Description

  The present invention relates to an object detection device.

  Japanese Patent Application Laid-Open No. 2004-133826 irradiates intensity-modulated irradiation light within an imaging range of an image sensor such as a CCD, and changes luminance in synchronization with intensity modulation of irradiation light from a captured image obtained by imaging the reflected light. A technique for extracting a synchronous detection region to be detected and detecting an object within an imaging range based on the synchronous detection region is disclosed.

JP 2008-128792 JP

However, in the above prior art, when the disturbance light such as sunlight changes from a weak situation to a strong situation, imaging is performed by adjusting the lens aperture value and the exposure time in order to suppress saturation of the output signal of the captured image. When the luminance output with respect to the light input of the element is reduced, the sensitivity resolution with respect to the irradiation light is lowered, so that there is a problem that the extraction of the synchronous detection region becomes unstable.
An object of the present invention is to provide an object detection apparatus that can stably extract a synchronous detection region regardless of changes in the intensity of disturbance light.

  In the present invention, the luminance representing the relationship between the light input and the luminance output in the region between the region where the luminance output value with respect to the light input of the imaging means is low and the region on the coordinates having the light input and the luminance output as the coordinate axes. The output characteristic is set, and the position in the light input axis direction is changed while maintaining the inclination of the luminance output characteristic according to the luminance of each pixel in the irradiation range of the light projecting means.

  Therefore, since the sensitivity resolution with respect to the irradiation light is kept constant, the synchronous detection region can be stably extracted regardless of the intensity change of the disturbance light.

It is a block diagram which shows the structure of the object detection apparatus of Example 1. FIG. 3 is a flowchart illustrating a flow of object detection processing by the object detection device according to the first embodiment. It is a figure which shows the change of the sensitivity resolution of an image pick-up element by the strength of disturbance light. It is a figure which shows the change of the luminance output characteristic of an image pick-up element at the time of adjusting the aperture value and exposure time of a lens according to the strength of disturbance light. In Example 1, it is a figure which shows the state which offset the luminance output characteristic with respect to the light input of an image pick-up element in the optical input-axis positive direction according to the luminance value in the irradiation area | region of the light projection part 1. FIG.

[Example 1]
FIG. 1 is a block diagram illustrating a configuration of the object detection apparatus according to the first embodiment. The object detection apparatus according to the first embodiment is mounted on a vehicle and detects an object in front of the vehicle.
The light projecting unit (light projecting means) 1 is, for example, a headlight provided with a projector headlight or a reflector, and irradiates irradiation light having a light distribution characteristic that forms a light emitting region in the horizontal direction toward the front of the vehicle. As the light source of the light projecting unit 1, visible light, infrared light, or ultraviolet light can be used.

The imaging unit (imaging means) 2 includes a camera 21, an offset circuit 22, and an AD converter 23.
The camera 21 includes an image sensor such as a CCD image sensor or a CMOS image sensor. The camera 21 captures an image of the front of the vehicle and, in addition, receives the reflected light of the irradiation light emitted by the light projecting unit 1.
The offset circuit (luminance output characteristic changing means) 22 gives a DC offset amount corresponding to an offset control signal (luminance output offset value) described later to the analog signal output from the camera 21.
The AD converter 23 converts the analog signal output from the offset circuit 22 into a digital signal.

  A modulation control unit (light projection control means, exposure control means) 3 outputs a trigger signal for imaging timing by the camera 21 and a control signal for exposure time (shutter time), and performs PWM control of the irradiation light of the light projection unit 1 The trigger signal of the timing of turning on and off the light is output. It also outputs the carrier wave (carrier frequency) signal used in PWM control.

  The synchronous detection processing unit (synchronous detection processing means) 4 sequentially stores the digital signal output from the AD converter 23, that is, the captured image of the camera 21, and stores all the pixels in the stored image (or the processing region in the image). In the case of restriction, all the pixels in the image processing area) are subjected to synchronous detection of the modulation signal included in the irradiation light output from the modulation control unit 3, so that only pixels whose luminance changes in synchronization with the irradiation light intensity are detected. The extracted synchronous detection area image is output.

The detection image edge detection unit 5 detects the position of the upper edge portion of the irradiated light from the synchronous detection region image extracted by the synchronous detection processing unit 4, and outputs the vertical position information in the image.
The object detection unit (object detection means) 6 uses the vertical position information of the upper edge detected by the detection image edge detection unit 5, and the angle and layout formed by the irradiation direction of the irradiation light upper edge and the visual axis of the camera 21 Based on the above, by calculating the distance to the object irradiated with the irradiation light based on the principle of triangulation, the determination of the three-dimensional object in the imaging range and the determination of the object are performed, and the detection result is output.

  The luminance detection unit (luminance detection means) 7 calculates the average value of the luminance output value and the standard deviation σ from the pixel output in the image region (irradiation region) where the irradiation light of the light projecting unit 1 is observed, and the irradiation region The DC offset amount of the offset circuit 22 using the conversion table recorded in the sensitivity characteristic storage unit 8 in advance so that the luminance value of the average luminance output of −3σ becomes the minimum luminance output output from the imaging unit 2. Is generated and output to the offset circuit 22. The conversion table is set so that the DC offset amount increases as the average value of the luminance output values increases.

  In the first embodiment, a region between a region where the luminance output value with respect to the light input of the image sensor is low and a region on the two-dimensional coordinate having the light input of the image sensor of the camera 21 as the horizontal axis and the luminance output as the vertical axis. The luminance output characteristic that represents the relationship between the light input and the luminance output in the camera is set, and the gradient of the luminance output characteristic provides sufficient sensitivity resolution for the irradiated light. The modulation control unit 3 sets default values for the lens aperture value and the exposure time so that the inclination can be extracted. Hereinafter, the luminance output characteristic at this time is referred to as a predetermined luminance output characteristic.

[Object detection processing]
FIG. 2 is a flowchart illustrating a flow of object detection processing by the object detection apparatus according to the first embodiment.
In step S1, the imaging unit 2 captures and acquires an image ahead of the vehicle.
In step S2, the luminance detection unit 7 calculates the average value of the luminance output values and the standard deviation σ from the pixel output of the irradiation region.
In step S3, the luminance detection unit 7 determines whether or not the luminance value of the average luminance value −3σ of the luminance output in the irradiation region is the minimum luminance output output from the imaging unit 2, and if YES, step S5 If NO, proceed to step S4.

In step S4, the luminance detection unit 7 generates an offset control signal such that the luminance value of the average luminance value −3σ of the luminance output in the irradiation region becomes the minimum luminance output output from the imaging unit 2, and the offset circuit 22 Then, offset control is performed to give a DC offset amount corresponding to the offset control signal to the analog signal output from the camera 21.
In step S5, the modulation control unit 3 determines whether or not the luminance value of the luminance output within the irradiation region + 3σ is less than or equal to the maximum luminance output output from the imaging unit 2, and if YES, the step Proceed to S7. If NO, proceed to Step S6.

In step S6, the modulation control unit 3 adjusts the exposure time of the camera 21 so that the luminance value of the average value of luminance output in the irradiation region + 3σ does not exceed the maximum luminance output output from the imaging unit 2.
In step S7, the synchronous detection processing unit 4 performs synchronous detection processing for extracting a synchronous detection region from the captured image.
In step S8, the detection image edge detection unit 5 detects the position of the upper edge portion of the irradiation light from the synchronous detection region image, and outputs the vertical position information.
In step S9, the object detection unit 6 performs object determination from the vertical position information of the upper edge.

Next, the operation will be described.
FIG. 3 plots the luminance output with respect to the light input of the image sensor of the camera on two-dimensional coordinates with the light input as the horizontal axis and the luminance output as the vertical axis. Usually, in an image sensor such as a CCD image sensor or a CMOS image sensor, a region where the luminance output continuously changes with respect to light input is a region where the luminance output value with respect to light input is low (region 1 in FIG. 3) and a region where the luminance output value is high (see FIG. 3). 3 area 3) and an area between them (area 2 in FIG. 3). In regions where the luminance output value is low and high, the amount of change in luminance output with respect to the amount of change in light input is small, and in the region between them, the amount of change in luminance output with respect to light input is large. Here, the relationship between the light input and the luminance output in the region between the region where the luminance output value is low and the region where the luminance output value is high is defined as a luminance output characteristic, and the characteristic is a straight line having a large slope. Here, when the disturbance light is weak, the fluctuation range of the luminance output with respect to the intensity modulation width of the irradiation light is large. Therefore, by setting the luminance output characteristic as shown in FIG. 3, the synchronous detection region is stabilized from the captured image. Can be extracted with high accuracy. However, since the intensity modulation width of the irradiation light is constant regardless of the intensity of the disturbance light, when the disturbance light is strong, the fluctuation range of the luminance output with respect to the intensity modulation width of the irradiation light becomes small.

  In the case of FIG. 3, when the disturbance light is strong, the output signal of the image sensor does not fall within the range of the luminance output characteristics and is saturated, so in practice, the aperture value of the lens is increased as shown in FIG. It is necessary to avoid saturation of the output signal by shortening the exposure time so that the maximum luminance output of the image sensor does not exceed the maximum value of the luminance output characteristics. However, when the disturbance light is strong, the method of reducing the slope (gain) of the luminance output characteristics by adjusting the aperture value and exposure time of the lens is accompanied by a decrease in sensitivity resolution with respect to the irradiated light, so the detection of the synchronous detection region is unstable. It becomes.

  On the other hand, in the first embodiment, the luminance detection unit 7 generates an offset control signal corresponding to the luminance value in the irradiation region of the light projecting unit 1, and the offset circuit 22 converts the analog signal output from the camera 21 into an analog signal. On the other hand, a DC offset amount corresponding to the offset control signal is given. The luminance detection unit 7 generates an offset control signal such that the DC offset amount increases as the average luminance value of the irradiation region increases. As a result, as shown in FIG. 5, the luminance output characteristics of the image sensor (camera 21) are offset in the positive direction of the light input axis as the disturbance light is stronger. At this time, since the inclination of the luminance output characteristic is maintained as the inclination of the predetermined luminance output characteristic, a decrease in sensitivity resolution with respect to the irradiation light can be avoided. That is, in the first embodiment, the synchronous detection region can be stably extracted regardless of the intensity change of the disturbance light by offsetting the position in the light input axis direction while maintaining the inclination of the luminance output characteristic.

  In the first embodiment, the luminance output characteristic of the image sensor is adjusted so that the luminance value of the average value −3σ of the luminance output in the irradiation area of the light projecting unit 1 becomes the minimum luminance output output from the imaging unit 2. Offset in direction. That is, the DC offset amount is set so that the minimum luminance value of the average value −3σ of the luminance output in the irradiation area of the light projecting unit 1 becomes the minimum value of the luminance output characteristics. Thereby, since the luminance output characteristic of the image sensor with respect to the irradiation light at the minimum intensity becomes linear, it is possible to set an efficient luminance sensitivity.

  In the first embodiment, the offset circuit 22 applies a DC offset amount corresponding to the luminance output offset value to the analog signal output from the camera 21. That is, since the offset is performed in the area of the analog signal before being converted into the digital signal by the A-D converter 23, the sensitivity range can be adjusted without reducing the resolution of the digital signal output from the A-D converter 23.

  In the first embodiment, the exposure time of the camera 21 is adjusted so that the luminance value of the average value + 3σ of the luminance output in the irradiation area of the light projecting unit 1 does not exceed the maximum luminance output output from the imaging unit 2. That is, the exposure time is set so that the maximum luminance value of the luminance output in the irradiation area of the light projecting unit 1 does not exceed the maximum value of the luminance output characteristics. That is, the gradient (gain) of the luminance output characteristic is adjusted only when the offset cannot be dealt with only by the luminance output characteristic offset (when the output signal is saturated). As a result, the synchronous detection region can be extracted efficiently while preventing saturation of the output signal.

In Example 1, the following effects are exhibited.
(1) The imaging unit 2 that captures an image, the light projecting unit 1 that irradiates intensity-modulated irradiation light within the imaging range of the image capturing unit 2 in synchronization with the exposure time of the image capturing unit 2, and the light projecting unit 1 The modulation control unit 3 that controls the emission intensity of the irradiation light, and the synchronous detection processing unit 4 that extracts a synchronous detection region whose luminance varies in synchronization with the intensity modulation of the irradiation light of the light projecting unit 1 from the captured image of the imaging unit 2 And an object detection unit 6 that detects an object within the imaging range from the synchronous detection region, and detects a luminance value of each pixel in the irradiation range of the light projecting unit 1 from the captured image of the imaging unit 2 The relationship between the light input and the luminance output in the region between the region where the luminance output value for the light input of the imaging unit 2 is low and the region on the coordinates with the light input and the luminance output as the coordinate axes is the luminance detection unit 7. The brightness output characteristics to be expressed are set, and the slope of the brightness output characteristics is maintained according to the brightness value of each pixel in the irradiation range. An offset circuit 22 to change the position of the optical input axis, comprising a.
Therefore, the synchronous detection region can be extracted stably regardless of the intensity change of the disturbance light.

(2) The offset circuit 22 offsets the luminance output characteristic of the imaging unit 2 in the positive direction of the optical input axis based on an offset control signal that increases as the luminance value of the irradiation range increases.
Therefore, the synchronous detection region can be extracted stably regardless of the intensity change of the disturbance light.

(3) The offset circuit 22 calculates the average luminance value and the standard deviation σ of the imaging range where the irradiation light of the light projecting unit 1 is observed, and the minimum luminance value of the average value −3σ is the minimum value of the luminance output characteristics. Thus, the luminance output characteristic of the imaging unit 2 is offset in the positive direction of the optical input axis.
Therefore, efficient luminance sensitivity can be set.

(4) The offset circuit 22 gives a DC offset amount corresponding to the offset control signal to the analog signal output from the imaging unit 2.
Therefore, the sensitivity range can be adjusted without reducing the resolution of the digital signal actually output from the imaging unit 2.

(5) A modulation control unit 3 that controls the exposure time of the imaging unit 2 is provided, and the modulation control unit 3 is configured such that the maximum luminance value of the imaging region where the irradiation light of the light projecting unit 1 is observed is the highest luminance output characteristic. Set the exposure time so as not to exceed.
Therefore, the synchronous detection region can be extracted efficiently while preventing saturation of the output signal of the image sensor.

(Other examples)
As mentioned above, although the form for implementing this invention was demonstrated based on the Example, the concrete structure of this invention is not limited to an Example, The design change of the range which does not deviate from the summary of invention And the like are included in the present invention.
For example, in the embodiment, the object detection device mounted on a vehicle is illustrated as an example of the present invention. However, the present invention is not limited to this, and for example, railways, ships, other mobile objects, industrial robots, security robots, nursing robots, The present invention can also be applied to devices that control the operation of robots, industrial devices, etc., and devices that measure the position of a stationary object or a moving object, and the same effects as in the embodiments can be obtained.

1 Emitter (emitter means)
2 Imaging unit (imaging means)
3 Modulation control unit (light projection control means, exposure control means)
4 Synchronous detection processing unit (Synchronous detection processing means)
6 Object detection unit (object detection means)
7 Luminance detection unit (luminance detection means)
22 Offset circuit (luminance output characteristic changing means)

Claims (5)

An imaging means for capturing an image;
A light projecting unit that irradiates intensity-modulated irradiation light within an imaging range of the imaging unit in synchronization with an exposure time of the imaging unit;
Projection control means for controlling the emission intensity of the irradiation light of the projection means;
Synchronous detection processing means for extracting a synchronous detection region whose luminance varies in synchronization with intensity modulation of irradiation light of the light projecting means, from a captured image of the imaging means;
Object detection means for detecting an object within the imaging range from the synchronous detection region;
In an object detection apparatus having
A luminance detecting means for detecting the luminance of each pixel in the irradiation range of the light projecting means from a captured image of the imaging means;
A luminance output characteristic representing the relationship between the light input and the luminance output in a region between a region where the luminance output value with respect to the light input of the imaging means is low and a region on the coordinate having the light input and the luminance output as coordinate axes. A luminance output characteristic changing unit configured to change the position of the light input axis direction while maintaining the inclination of the luminance output characteristic according to the luminance of each pixel in the irradiation range;
An object detection apparatus comprising: The object detection apparatus according to claim 1,
The luminance output characteristic changing unit offsets the luminance output characteristic of the imaging unit in the positive direction of the light input axis based on a luminance output offset that increases as the luminance of the irradiation range increases. The object detection device according to claim 2,
The luminance output characteristic changing unit calculates an average luminance and a standard deviation σ of an imaging range where the irradiation light of the light projecting unit is observed, so that a minimum luminance of an average value −3σ becomes a minimum of the luminance output characteristic. An object detection apparatus that offsets the luminance output characteristic of the imaging means in the positive direction of the light input axis. In the object detection device according to claim 2 or 3,
The luminance output characteristic changing unit adds an amount of direct current offset corresponding to the luminance output offset to the analog signal output from the imaging unit. In the object detection device according to any one of claims 1 to 4,
Exposure control means for controlling the exposure time of the imaging means;
The object detection apparatus, wherein the exposure control means sets an exposure time so that a maximum luminance of an imaging region where the irradiation light of the light projecting means is observed does not exceed a maximum of the luminance output characteristics.

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