Application of Image Brightness Measurement Technology in Road Lighting Test

Foreword

The purpose of road lighting is to create a good visual environment for various vehicle drivers and pedestrians, to ensure traffic safety, improve transportation efficiency, facilitate people's lives, reduce crime rates and beautify the environment. Road lighting design has long been based on the “illumination standard” of the road surface. Along with advances in human physiology research, it was found that the brightness of the road surface and the brightness of the light curtain caused by the stray light of the road lighting fixture at the eye can better evaluate and predict the visibility of objects on both sides of the road and the road. Since the publication of CIE No.12.2, the "Recommendations for Motor Vehicle Traffic Road Lighting" in 1977, the concept of road surface brightness has been gradually recognized and accepted by road lighting design standards, and gradually became a road directional design in the 1980s. standard. China's "Urban Road Lighting Design Standards" CJJ45-2006 also stipulates the average brightness of road lighting, total uniformity of road surface brightness, longitudinal uniformity, glare limitation, etc. according to road use functions and traffic flow.

1 Road pavement brightness detection method and instrument requirements

"Lighting Measurement Method" GB/T5700-2008 has made corresponding regulations on road surface brightness measurement methods and techniques.

1.1 Luminance meter

In road illumination measurement, when it is necessary to measure the total brightness uniformity and the longitudinal uniformity of brightness, it is preferable to use a illuminometer with a telescope head whose viewing angle in the vertical direction should be less than or equal to 2', and the angle of view in the horizontal direction should be 2'~20'.

1.2 Brightness measurement method

The height of the observation point of the luminance meter should be 1.5 m from the road surface. The longitudinal position of the observation point of the luminance meter: 60m from the first row of measurement points and 100m in the longitudinal direction (Fig. 1).

Application of Image Brightness Measurement Technology in Road Lighting Test

In the longitudinal direction of the road, when the distance between the two poles on the same side is less than or equal to 50m, 10 measuring points should normally be arranged at equal intervals between the two poles; when the spacing between the two poles is greater than 50 m, the spacing between the two measuring points should be less than The principle of equal to 5 m determines the number of points. In the horizontal direction of the road, five measuring points should be arranged in the horizontal direction of each lane. One of the points should be located on the center line of the lane. The two outermost points on both sides should be located at 1/10 of the boundary line on each side of each lane. Lane width; when the brightness uniformity is good or the accuracy of the measurement is low, 3 points can be arranged in the horizontal direction of each lane. One point should be located on the center line of each lane, and two points on both sides They should be located 1/6 lane wide from the boundary line on either side of each lane. According to the above measurement method, the measurement takes a long time, the efficiency is low, and there is no vehicle interference on the road, but in fact, there are more and more motor vehicles on the road, and sometimes the speed is fast, so there is a great safety hazard.

CCD cameras are widely used in research fields where it is desirable to simultaneously obtain an array of digital radiation values ​​with good linearity and accuracy. Cameras that use CCDs can quickly capture images and turn them into digital electronic images. Image measurement is especially suitable for targets with intensive points to be measured, and is suitable for targets whose target environment is not stable or even drastically changed. If a reasonable control method is used, by determining the value of any pixel of the camera CCD array, the brightness value of the point in the mapped environment can be determined, and the scene uniformity and contrast are obtained through correlation calculation.

As early as 2009, China Academy of Building Research completed the topic "Research on Image Brightness Measurement Technology Based on Digital Cameras", which is the three major factors affecting the camera's measurement of brightness and chromaticity parameters (optical systems, electronic systems and image processing). The algorithm) has been carefully studied. Through experimental research and computer simulation analysis, the optical system error simulation test analysis, CCD characteristic experiment, the measurement range of the camera brightness measurement is obtained. Especially through the research on the decoding technology of Canon camera RAW file, the loss of precision and data linearity caused by using jpeg compressed file as the measurement result carrier is avoided, and the test precision and the brightness of single picture can be further improved. range. These efforts have important guiding significance for the final development of image-based luminance meters with lower prices and good marketing value. Through the research of this technology, the traditional image brightness measurement technology has been greatly improved, as shown in the following table:

Application of Image Brightness Measurement Technology in Road Lighting Test

By comparison, the main performance indicators of the research results of this subject are better than the main research results at home and abroad. At the appraisal meeting of the research results, the appraisal experts agreed that the research results have reached the international advanced level.

2.1 Application of Image Brightness Measurement Technology in Road Lighting Test

After the completion of the project identification, our institute has carried out corresponding verification work on the application of image brightness measurement technology in road lighting test. In the test of road lighting projects in Sichuan Province and Guizhou Province (Figure 2), the traditional measurement method and image brightness measurement technology were compared. The test results show that the image measurement technology test results are basically consistent with the traditional measurement methods (maximum test error is 7%), and the test efficiency is greatly improved, further confirming the application value of the technology in road lighting test practice.

Application of Image Brightness Measurement Technology in Road Lighting Test

2.2 Current work

The current image luminance meter can only record the brightness information in the field of view. However, due to the distortion of the lens itself, the size and orientation of the light-emitting object cannot be accurately reflected. At present, the research on geometric correction technology of image brightness measurement, which is being carried out in our hospital, will comprehensively consider the effects of radial distortion, eccentric distortion and thin lens distortion of the camera lens to establish a mathematical model of camera distortion, so as to accurately obtain the measurement field of view. Different geometric information in . At present, the main research work has been completed, and the project identification and acceptance work will be completed in the near future. It is believed that with the development of this project, image brightness measurement technology can be better applied in the practice of road lighting in China.

3 Summary

This paper introduces the application of image brightness measurement technology in road lighting test by digital camera. Through the comparison of the results of traditional brightness test methods in related projects, the application potential of this technology in road lighting test practice is further verified. It is believed that with the in-depth development of related technology research, image brightness measurement technology will greatly promote the development and technology improvement of road lighting inspection in China, thus providing technical support for the development of road lighting in China.

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