Headlight tester beam axis calculation system

Abstract

To provide an optical axis calculation system of a headlight tester, which can achieve both of noise reduction and application of an algorithm using a luminance gradient.SOLUTION: An optical axis calculation system includes an optical axis camera 5 capable of performing imaging with multiple exposure. A synthetic luminance value of each pixel is calculated from each one of images (the image of a light distribution pattern radiated to a screen 4) acquired by imaging with multiple exposure by the optical axis camera 5, thereby to set cut-off lines where the maximum value and the minimum value of a curve to be obtained by differentiating twice an edge point on a synthetic image acquired based on the synthetic luminance value as elbow points. Thus, both of noise reduction and application of an algorithm using a luminance gradient are achieved.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical axis calculation system for a headlight tester, and more particularly to an improvement for obtaining high optical axis calculation accuracy. [Background technology]

[0002] Conventionally, headlamps of vehicles have been tested with a headlight tester to determine whether their light distribution pattern (specifically, the light distribution pattern of a low beam headlight for passing other vehicles) is within the standard range set by vehicle safety standards.

[0003] In the test of the light distribution pattern by the headlight tester, as disclosed in Patent Document 1, for example, the vehicle and the headlight tester are faced to each other, the light distribution pattern irradiated from the headlights onto the screen is photographed by a camera or the like, the photographed image is processed to obtain an elbow point of the cutoff line (also called a clear boundary line), and it is inspected whether the elbow point is in a position within a predetermined standard range (for example, the deviation amount of the elbow point when irradiating a predetermined distance ahead is within a predetermined range). As is well known, this elbow point is the intersection point of the horizontal cutoff line (horizontal cutoff line set on the oncoming vehicle side) and the oblique cutoff line (oblique cutoff line set on the own vehicle side (road shoulder side)) in the light distribution pattern. In order to improve the calculation accuracy of the optical axis (the irradiation direction of the light irradiated from the headlights), it is necessary that this elbow point be obtained stably. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-79359 A Summary of the Invention [Problem to be solved by the invention]

[0005] High accuracy is required for calculating the optical axis of the light distribution pattern, but noise exists for each pixel in an image of a light distribution pattern captured by a camera, etc. For this reason, even a small change in the amount of light from the lamp causes the brightness value to change, particularly near the edge (the point where the amount of change in brightness value in the y direction (up and down direction) in the light distribution pattern is maximum), making the cutoff line unstable and causing the elbow point to flicker on the image. In such a situation, the elbow point cannot be obtained stably, and therefore high accuracy in calculating the optical axis cannot be obtained.

[0006] Although the noise can be reduced by increasing the exposure of the camera, in this case, the luminance of the entire image increases, which makes it easier for the luminance to reach the upper limit of the gradation, preventing the application of an algorithm using a luminance gradient (an algorithm that determines the maximum position of the amount of change in luminance value as an edge). For this reason, in the conventional technology, it was difficult to reduce noise and apply an algorithm using a luminance gradient at the same time.

[0007] The present invention has been made in consideration of the above points, and an object of the present invention is to provide an optical axis calculation system for a headlight tester that is capable of achieving both noise reduction and the application of an algorithm that uses a luminance gradient. [Means for solving the problem]

[0008] The solution of the present invention for achieving the above object is based on an optical axis calculation system for a headlight tester that calculates the optical axis of a vehicle headlamp. The optical axis calculation system for the headlight tester includes an image capturing means capable of capturing images with multiple exposures, a composite brightness value calculation unit that calculates a composite brightness value of each pixel from each image acquired by capturing images with multiple exposures with the image capturing means, and an optical axis calculation unit that calculates the optical axis of the headlamp based on the composite brightness value calculated by the composite brightness value calculation unit. The optical axis calculation unit is configured to sequentially perform an edge calculation operation for extracting an area in which an elbow point, which is an intersection point between a horizontal cutoff line and an oblique cutoff line in a light distribution pattern, is estimated to exist from a synthetic image created from the synthetic luminance value for each pixel, and detecting a position where an amount of change in the synthetic luminance value becomes large when an area near the cutoff line in the vertical direction is scanned for the extracted image; a differentiation operation for performing a second differentiation operation on a line recognized as an edge by the edge calculation operation; and a cutoff line setting operation for performing a straight-line approximation process based on a maximum point and a minimum point in a curve obtained by the differentiation operation to obtain a first horizontal cutoff line extending horizontally to one side of a position corresponding to the maximum point and a second horizontal cutoff line extending horizontally to the other side of a position corresponding to the minimum point, and to obtain an oblique cutoff line connecting the maximum point and the minimum point, and to determine an intersection point between the first horizontal cutoff line and the oblique cutoff line and an intersection point between the second horizontal cutoff line and the oblique cutoff line as the elbow point, respectively. It is characterized by:

[0009] Due to this specification, the composite luminance value calculated from each image acquired by multiple exposure photography by the photography means is obtained as a value in which noise that existed in each image with different exposures is reduced by canceling each other out. Also, since the luminance value is calculated by combining multiple images, information on the luminance value with infinite gradation is obtained. Therefore, the cutoff line of the light distribution pattern on the image obtained according to this composite luminance value can be obtained as a stable one, and the adjustment point of the optical axis (e.g., elbow point) can be obtained stably, and high optical axis calculation accuracy can be obtained. Effect of the Invention

[0010] In the present invention, a composite luminance value of each pixel is calculated from each image captured by multiple exposure photography using a photography means, and the optical axis of the headlamp is calculated based on the composite luminance value, which makes it possible to achieve both noise reduction and application of an algorithm using a luminance gradient. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of an optical axis calculation system. [Diagram 2] FIG. 2 is a control block diagram of the optical axis calculation system. [Diagram 3] 1A and 1B are diagrams showing an example of each image acquired by multiple exposure shooting and an example of a composite image of the images; [Figure 4] FIG. 2 is a diagram showing an example of the luminance value for each exposure in one pixel of each image acquired by multiple exposure shooting. [Diagram 5] 11A and 11B are diagrams for explaining a data narrowing-down operation in the composite luminance value calculation process. [Figure 6] 11A and 11B are diagrams for explaining a linear model creation operation in the composite luminance value calculation process. [Figure 7] 11A and 11B are diagrams for explaining a reference exposure calculation operation in the composite brightness value calculation process. [Figure 8]11A and 11B are diagrams for explaining an edge calculation operation of a composite image in the optical axis calculation process. [Figure 9] 13A to 13C are diagrams for explaining a differential operation for an edge of a composite image in the optical axis calculation process. [Figure 10] 11A to 11C are diagrams for explaining a cutoff line setting operation in the optical axis calculation process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] -Outline of the optical axis calculation system- 1 is a schematic diagram showing a schematic configuration of an optical axis calculation system 1 of a headlight tester according to this embodiment. Although not shown, this optical axis calculation system 1 is supported by a support pillar erected on a dolly of the headlight tester. The dolly is free to move in the horizontal direction (for example, horizontal movement on a rail). In addition, the optical axis calculation system 1 is free to move in the vertical direction relative to the support pillar (up and down movement by a lifting mechanism). This allows the optical axis calculation system 1 to be directly faced to the headlamp HL of the vehicle to be tested.

[0014] The optical axis calculation system 1 has a configuration in which a Fresnel lens 3, a screen 4, and an optical axis camera (imaging means) 5 are housed in a casing 2, and a facing camera 6 is mounted on the top of the casing 2.

[0015] The Fresnel lens 3 is disposed on the front surface of the casing 2 (the surface facing the vehicle headlamp HL) and has a central optical axis extending horizontally. The Fresnel lens 3 collects the light (illuminated light) irradiated from the vehicle headlamp HL and transmits it toward the inside of the casing 2 (toward the screen 4).

[0016] The screen 4 receives the irradiated light collected by the Fresnel lens 3. As a result, the light distribution pattern of the light irradiated from the headlamp HL of the vehicle is projected onto the screen 4. In this light distribution pattern, a large difference in brightness occurs at the boundary between the part where the light hits and becomes bright and the part where the light does not hit and becomes dark, and a cutoff line occurs. As described above, this cutoff line is composed of a horizontal cutoff line and an oblique cutoff line. The horizontal cutoff line is set on the oncoming vehicle side and extends horizontally at a predetermined height position so as not to dazzle the driver of the oncoming vehicle. The oblique cutoff line is set on the vehicle side (shoulder side) and extends upward toward the shoulder side to increase the visibility of pedestrians walking on the shoulder. The intersection point of these horizontal cutoff lines and oblique cutoff lines is called an elbow point, and in testing the light distribution pattern with a headlight tester, it is inspected whether this elbow point is located within a predetermined standard range (for example, the amount of deviation of the elbow point when irradiating a predetermined distance ahead is within a predetermined range). In addition, there are cases where a horizontal cutoff line is set on the road shoulder side of the diagonal cutoff line.

[0017] The optical axis camera 5 is composed of, for example, a CCD (Charge Coupled Device) camera or a CMOS (Complementary Metal Oxide Semiconductor) camera, and is disposed on the rear side of the screen 4 so that its optical axis coincides with the optical axis of the Fresnel lens 3. The optical axis camera 5 is capable of multiple exposure photography, and is capable of photographing the light distribution pattern of the irradiated light projected onto the screen 4 while changing the exposure in multiple steps (for example, 15 steps). The number of multiple exposure steps is not limited to the above. Exposure adjustment parameters for realizing this multiple exposure include the shutter speed, the aperture value of the photographing lens, and the ISO sensitivity value.

[0018] The facing camera 6 is used to face the optical axis calculation system 1 (more specifically, the Fresnel lens 3 and the optical axis camera 5) to the headlamp HL of the vehicle, and is used to determine whether the headlamp HL is facing forward by photographing a vehicle stopped in front of the optical axis calculation system 1. In other words, the optical axis calculation by the headlight tester is performed in a state where it is determined that the headlamp HL is facing forward based on the image photographed by the facing camera 6. Note that, instead of the facing camera 6, a known facing laser sight or the like can be applied.

[0019] -Control system configuration of the optical axis calculation system- Next, the configuration of the control system of the optical axis calculation system 1 will be described. Fig. 2 is a control block diagram of the optical axis calculation system 1. The control system of the optical axis calculation system 1 includes, as a hardware configuration, a processor such as a CPU (Central Processing Unit), a ROM (Read-Only Memory) that stores a control program, a RAM (Random-Access Memory) that temporarily stores data, and an input / output port. These hardware components may be built into the optical axis camera 5, or may be configured as a control unit separate from the optical axis camera 5.

[0020] The control system of the optical axis calculation system 1 has a function of calculating a composite luminance value of each pixel from each image acquired by multiple exposure shooting using the optical axis camera 5, and calculating the optical axis of the headlamp HL (the irradiation direction of the light emitted from the headlamp HL) based on the calculated composite luminance value. FIG. 3 is a diagram showing an example of each image acquired by multiple exposure shooting and an image of the composite image. FIGS. 3(a)-(b) show examples of each image captured with different exposures. Although only two images are shown here, images corresponding to the number of stages of multiple exposure will be captured. For example, 15 images with different exposures will be captured. FIG. 3(c) shows an example of a composite image created based on these images (each image with different exposures).

[0021] In order to realize the above-mentioned function of calculating the composite brightness value, the control system of the optical axis calculation system 1 includes, as functional units realized by the control program, an image receiving unit 71, a composite brightness value calculation unit 72, and an optical axis calculation unit 73, as shown in FIG. 2.

[0022] The image receiving unit 71 acquires data of each image (image data by exposure) taken with different exposures for the same test object (light distribution pattern of the light irradiated by the headlamp HL) by the optical axis camera 5. The data of these images is temporarily stored in the RAM.

[0023] The composite luminance value calculation unit 72 uses the data of each image to calculate a composite luminance value by utilizing the change in luminance value in response to the change in exposure for each pixel on the image.

[0024] The following describes the composite brightness value calculation process performed by composite brightness value calculation unit 72. In this composite brightness value calculation process, a data narrowing down operation, a linear model creation operation, and a reference exposure calculation operation are performed in this order.

[0025] First, when the composite luminance value calculation process starts, data of the luminance value corresponding to the exposure at each pixel in each image acquired by multiple exposure shooting is acquired. This is because when shooting is performed with a certain exposure, the luminance value of each pixel on the shot image is acquired, and the exposure and the luminance value are acquired as information associated with each pixel. Therefore, when shooting with all exposures is completed, information associated with the number of exposures and the luminance value corresponding to the product of the number of exposures and the number of pixels in the image is acquired. FIG. 4 is a diagram showing an example of the luminance value (vertical axis) for each exposure (horizontal axis) in one pixel of each image acquired by multiple exposure shooting. As shown in FIG. 4, most of the luminance values ​​increase as the exposure increases. Note that in FIG. 4, due to the influence of disturbances, etc., there is data in which the luminance value appears small even when the exposure increases.

[0026] Fig. 5 is a diagram for explaining the data narrowing down operation. This data narrowing down operation is to eliminate data from the data shown in Fig. 4 in which the luminance value for the exposure may not be appropriately obtained due to the influence of disturbances or the like. In Fig. 5, data in the range where the exposure is equal to or less than a predetermined value ex1 and equal to or more than a predetermined value ex2 (data in the ranges shaded in Fig. 5) are eliminated, so that only information with high reliability in the relationship between the exposure and the luminance value remains. The predetermined values ​​ex1 and ex2 can be set arbitrarily.

[0027] Fig. 6 is a diagram for explaining the linear model creation operation. For the data (data showing the relationship between exposure and luminance value) narrowed down by the above-mentioned data narrowing down operation, a linear model "y = ax + b" is obtained by the least squares method. The coefficient a here represents the slope of the linear model, and indicates the rate of increase in luminance value with respect to increase in exposure.

[0028] For example, the region above the cutoff line (the region above the region near the cutoff line) is a region that is darkened by no light, so the luminance value hardly increases even if the exposure is increased. For this reason, the pixels in this region are obtained as having a small slope (coefficient a) in the linear model. Also, the region below the cutoff line (the region below the region near the cutoff line; for example, a hot zone with the maximum luminance value and its surrounding region) is a region that is brightened by light, so in this case too, the increase in luminance value is small even if the exposure is increased. For this reason, the pixels in this region are obtained as having a small slope in the linear model. On the other hand, in the region near the cutoff line, the luminance value increases significantly as the exposure is increased. For this reason, the pixels in this region are obtained as having a large slope in the linear model.

[0029] 7 is a diagram for explaining the reference exposure calculation operation. In this reference exposure calculation operation, an exposure corresponding to a preset reference value Y0 of the brightness value is calculated as a reference exposure X0 for the data (linear model data) obtained in the linear model creation operation. This reference value Y0 of the brightness value can be set arbitrarily.

[0030] After the reference exposure X0 is calculated for each pixel in this way, the reciprocal (1 / X0) is calculated and set as the composite luminance value corresponding to each pixel. In other words, the set of reference exposures X0 calculated for each pixel (X0∈R + ) is set as the composite brightness value v (v=1 / X0).

[0031] As described above, in the region above the cutoff line and the region below the cutoff line, the slope of the linear model is small, so the reference exposure X0 calculated for these pixels is relatively large, and the composite luminance value (1 / X0), which is the reciprocal of the reference exposure X0, is obtained as a small value. On the other hand, in the region near the cutoff line, the slope of the linear model is large, so the reference exposure X0 calculated for these pixels is relatively small, and the composite luminance value (1 / X0), which is the reciprocal of the reference exposure X0, is obtained as a large value. As a result, when the region near the cutoff line is scanned in the vertical direction, there is a position where the change in the luminance value (composite luminance value) is large, and by recognizing this position as the edge of the light distribution pattern, the edge can be stably obtained.

[0032] Next, a description will be given of the optical axis calculation process performed by the optical axis calculation unit 73. In this optical axis calculation process, a composite image is created from the composite luminance value for each pixel calculated by the composite luminance value calculation unit 72, and an edge calculation operation for calculating edges on this composite image, a differentiation operation for the edges of the composite image, and a cutoff line setting operation for setting a cutoff line are sequentially performed.

[0033] In the edge calculation operation, a predetermined area (an area where an elbow point is estimated to exist) is cut out from the composite image, and the area near the cutoff line in the cut-out image is scanned in the vertical direction as described above to detect the position where the change in luminance value (composite luminance value) becomes large. The line ED in Fig. 8 represents the edge set by this edge calculation operation.

[0034] In the differentiation operation, a second differentiation operation is performed on the line ED recognized as an edge by the edge calculation operation. FIG. 9 is a diagram (a diagram showing an enlarged portion of an image) for explaining this differentiation operation. The dashed-dotted line in FIG. 9 is an example of a curve obtained when a first differentiation operation is performed on the line ED recognized as an edge. The dashed-two-dotted line in FIG. 9 is an example of a curve obtained when a second differentiation operation is performed on the line ED recognized as an edge. The curve obtained by this second differentiation operation has a local maximum point (maximum point) P1 and a local minimum point (minimum point) P2.

[0035] In the cutoff line setting operation, as shown in FIG. 10(a), a cutoff line is set by performing a linear approximation process with a BOX based on the maximum point P1 and the minimum point P2 in the curve obtained by the second differentiation operation. As shown in FIG. 10(b), a first horizontal line (horizontal cutoff line) CL1 extending horizontally to the left of the position corresponding to the maximum point P1 and a second horizontal line CL2 extending horizontally to the right of the position corresponding to the minimum point P2 are obtained as the cutoff line. In this case, the second horizontal line CL2 is located a predetermined distance above the first horizontal line CL1 on the image. Then, a diagonal line (diagonal cutoff line) CL3 connecting the maximum point P1 and the minimum point P2 is obtained by the linear approximation process with the BOX. Then, an intersection point EL1 between the first horizontal line CL1 and the diagonal line CL3 and an intersection point EL2 between the second horizontal line CL2 and the diagonal line CL3 are obtained as elbow points. As described above, in the area near the cutoff line, a stable edge is obtained based on the composite luminance value, so that the cutoff line of the light distribution pattern on the image can also be obtained stably, the elbow points EL1 and EL2 can be obtained stably, and high optical axis calculation accuracy can be achieved.

[0036] In addition, when determining whether or not the elbow point is located within a predetermined standard range during an actual test (a test of a light distribution pattern using a headlight tester), the elbow point used in the test differs depending on the destination of the vehicle. For example, in Japan, etc., it is determined whether or not the intersection (elbow point) EL1 between the first horizontal line CL1 and the diagonal line CL3 is located within the standard range, and in the United States, etc., it is determined whether or not the intersection (elbow point) EL2 between the second horizontal line CL2 and the diagonal line CL3 is located within the standard range.

[0037] In addition, in a destination where the road is driven on the left side, the first horizontal line CL1 is located on the right side (oncoming vehicle side) as viewed from the vehicle side, and the diagonal line CL3 and the second horizontal line CL2 are located on the left side (shoulder side). In this embodiment, the optical axis camera 5 is disposed on the rear side of the screen 4, so that the first horizontal line CL1 is located on the left side, and the diagonal line CL3 and the second horizontal line CL2 are located on the right side, as shown in Figs. 8 and 10, in the acquired image. In contrast, in a destination where the road is driven on the right side, the first horizontal line CL1 is located on the left side (oncoming vehicle side) as viewed from the vehicle side, and the diagonal line CL3 and the second horizontal line CL2 are located on the right side (shoulder side). In this embodiment, the image acquired by the optical axis camera 5 is inverted left to right, so that the first horizontal line CL1 is located on the left side, and the diagonal line CL3 and the second horizontal line CL2 are located on the right side, as in the above-mentioned case (in the case of a destination where the road is driven on the left side). This makes it possible for the same optical axis calculation system 1 to be used equally in destinations where traffic is on the left and in destinations where traffic is on the right, thereby increasing the versatility of the optical axis calculation system 1.

[0038] -Effects of the embodiment- As described above, in this embodiment, the composite luminance value of each pixel is calculated from each image acquired by multiple exposure photography using the optical axis camera 5, and the elbow points EL1 and EL2 of the light distribution pattern of the headlamp HL are calculated based on the calculated composite luminance value. Therefore, the composite luminance value is obtained as a value in which noises that existed in each image with different exposures are canceled out by each other, and the noises are reduced. In addition, since the luminance value is calculated by combining multiple images, information on the luminance value with infinite gradation is obtained. Therefore, the cutoff line of the light distribution pattern on the image obtained according to this composite luminance value can be obtained as a stable one, and the adjustment point (elbow point) of the optical axis can be obtained stably, and high optical axis calculation accuracy can be obtained. In the conventional technology, when noise is reduced by increasing the exposure of the camera, the luminance easily reaches the upper gradation limit due to the increase in the luminance of the entire image, which prevents the application of an algorithm using a luminance gradient. However, in this embodiment, there is no need to use a means such as increasing the exposure of the camera to reduce noise, and therefore it is possible to achieve both noise reduction and application of an algorithm using a luminance gradient.

[0039] -Other embodiments- The present invention is not limited to the above-described embodiment, and all modifications and applications within the scope of the claims and equivalents thereto are possible.

[0040] For example, in the above embodiment, the light distribution pattern projected on the screen 4 is photographed by the optical axis camera 5 from the rear side of the screen 4. However, the present invention is not limited to this, and can also be applied to an optical axis calculation system for a headlight tester in which the light emitted from a headlamp is split by a half mirror and the split light is photographed by the optical axis camera. [Industrial Applicability]

[0041] The present invention is applicable to an optical axis calculation system for a headlight tester that can achieve both noise reduction and application of an algorithm using a luminance gradient. [Explanation of symbols]

[0042] 1. Optical axis calculation system 5. Optical axis camera (photography means) 72 Composite brightness value calculation unit 73 Optical axis calculation unit

Claims

[Claim 1] A headlight tester optical axis calculation system for calculating an optical axis of a headlamp of a vehicle, comprising: A photographing means capable of photographing with multiple exposures; a composite luminance value calculation unit that calculates a composite luminance value of each pixel from each image acquired by multiple exposure photography using the photography means; an optical axis calculation unit that calculates an optical axis of the headlamp based on the composite luminance value calculated by the composite luminance value calculation unit, The optical axis calculation unit an edge calculation operation of extracting an area where an elbow point, which is an intersection point between a horizontal cutoff line and an oblique cutoff line in a light distribution pattern, is estimated to exist from a composite image created from the composite luminance value for each pixel, and detecting a position where an amount of change in the composite luminance value becomes large when an area near the cutoff line is scanned in a vertical direction from the extracted image; a differentiation operation for performing a second differentiation operation on the line recognized as an edge by the edge calculation operation; a cutoff line setting operation for obtaining an intersection point between the first horizontal cutoff line and the oblique cutoff line and an intersection point between the second horizontal cutoff line and the oblique cutoff line as the elbow point, by performing straight-line approximation processing based on the maximum points and minimum points in the curve obtained by the differentiation operation, thereby obtaining a first horizontal cutoff line extending horizontally to one side of a position corresponding to the maximum point and a second horizontal cutoff line extending horizontally to the other side of the position corresponding to the minimum point, and also obtaining an oblique cutoff line connecting the maximum point and the minimum point, and

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