Overload intelligent detection method of lift platform’s number of people under auxiliary visual

Yue PANG

（Chongqing Jianzhu College，Chongqing 400072，China）

People counting is the key of the monitoring and control system of lift platform，and the number of workers on lift platform is the very important factor to the personal safety of workers and the safe operation of it［1-2］．Lift platform has very strict requirements in the number of workers，which always be neglected．Therefore it is necessary to have an accurate accounting of workers on the platform to avoid the overload operation and to make sure the personal safety of workers and the safe operation of lifter．Manufacturers can set the“overload protection”according to the load capability and self security feature of the lifter：when the weight of workers is over the rated weight，the audio will have an alarm sound and the lifter cannot run in order to ensure the personal safety of workers［3-4］．Now the detection of overload of lifter is mainly manual work and will be influenced by human factor，which has obvious disadvantages and lowers the accuracy of people counting on the platform［5］．

1 Preprocessing method for image acquisition of lift platform

1．1 Remoteimagetransmission principleof lift platform

The image acquisition equipment of the lift will have the collected image compression first，and then compression image will be remotely transmitted to the security monitoring system［6-7］．The steps are as follows．

Suppose that the number of workers on the platform lift is N，and workers image transmission distance isl，and the initial moment of image transmission is t0，and reaches moments of image to the security monitoring system is t1，and if the number of pixels of the arbitrary one frame of image Riis M，and the gray value of it is Si，the image data compression process can be calculated through formula（1）：

The above formula can calculate the image compression coefficient and can describe the degree of image compression．

Image resolution in security monitoring system can use formula（2）to calculate：

The above formula can calculate the resolution of the image，and can have the description of image definition．

1．2 Disadvantages of long-distance image transmission

From formula（1），we can see that the image compression coefficient decreases with the increase of the distance．Through formula（2），we can conclude that the decrease of image compression coefficient will reduce the resolution of the image in the security monitoring system．Because of the long distance between the elevator and security monitoring system，image will be affected by other factories interference source in the transmission process and the clarity of image will be reduced by compression，and therefore it contains a lot of noise．The traditional denoising methods are mainly image transmission method based on neural network algorithm and image transmission method based on ant colony algorithm and so on，whose denoising effect is not ideal，which leads to the poor clarity of image［8-9］．A new denoising method of image based on discrete wavelet transform was proposed．

Fig．1 Denoising effect of traditional algorithm

1．3 Denoising of lift platform image

Due to the long distance of communication and great external interference factors in the transmission process，the transmission of images of workers on the lift platform exists a large number of random noise，which leads to that staff in security monitoring system cannot have exact statistics of the number of workers in lift．After the Image being transmitted to the security monitoring system，the expansion of it is an image sequence，which is represented by g（y）．Using the formula（3），we can calculate the transformation of the image sequence：

If the parameters in the formula satisfy k≥k0，the following formula can be obtained：

g（y），γk0，l（y）andφk，l（y）in the above formula are all functions of the discrete variables．Collect arbitrarily sample y0，Δy，y＝1，2，…，N，g（y）＝g（y0，yΔy），and set k0＝0，N＝2′，and then y＝1，2，…，N，k＝1，2，…，K and l＝1，2，…，2′-1 can be summed up．Arbitrarily collect an image，and select four pixels g（0）＝1，g（1）＝4，g（2）＝-3 and g（3）＝0，and sum up y＝1，2，3，4，k＝1，2，and substitute the above four pixels into the above formula，we can get the following formula：

Using the above formula，we can sample the image features of the workers on the sample．According to the formula below，the sample can be collected from the similar interval：

According to the formula below，we can have discrete wavelet transform：

The method of discrete wavelet transform can remove the noise from outside factor and eliminate the noise caused by external factors，thus to improve the contour articulation of the image．

Fig．2 Comparison of the denoising effect of the proposed algorithm and the traditional denoising method

2 Personnel statistics based on image features

2．1 Gauss curve fitting process of personnel head

In the process of image processing，the computer is mainly based on the contour of workers．Contour feature is the discontinuity of gray value between the background and the target image．The main features of the contour of the lift platform are：①the gray value of the background contour is continuous；②the texture features of the contour of workers and the texture of the background are different；③the gray value of the edge pixels of the workers’contour has gradient changes．

Removing the noise of image acquisition can improve image clarity and improve the contour feature of the workers then．Using Gaussian curve fitting method，we had workers image processing，a Gaussian curve by deformation is as shown in equation（8）：

Set the curve of second degree is z＝By2＋Cy＋D，and then the gray value of pixels in the image of the workers can be calculated by using the formula（9）：

In Fig．3，we set the maxima of gray scale difference value is 0 point，with the corresponding gray value is g0，and set the approaching two pixels between-1 and 1，and the two corresponding to the pixel gray value are g-1and g1，then the following formula can be used to describe the three pixel gray value：

The values of point B，C，D can be calculated with the above formulas：

With the formula（13），the space position parameters of top point can be calculated：

After the logarithm transformation of the formula，as shown in the formula（14），the spatial position parameters of worker images can be obtained：

By calculating each of the pixels of the workers’image area，we can get a clear outline of the workers’images，as shown in Fig．4．

Fig．3 Curve fitting outline of worker images

Fig．4 Gauss curve fitting processing image

2．2 People counting and position marking

After the processing of statistics and labeling of the outline，the statistical ideas used in this paper are as follows：

1）The idea of the people counting of the image of a frame lift platform is：inputting the image，marking the number and outputting the image．We set these three array which are，Inimage represents inputting the image，Markimage represents a marker image（where 0 is the background，1 is the aim），Outimage represents outputting the image（where 1 is the first goal，and 2 is the second goal，and by parity of reasoning）respectively．

2）A scan was carried out from the periphery of an image，and tracked when scanned target of 1．In the scanning process，taking the boundary points of the contour as the target point to scan and if it found area points on the surrounding，it kept them in Outimage，while if it did not find pixel whose value is 1 around，the mark is over．After the end of the tag，it will continue to scan the remaining region for the pixels whose median is1．When it scans to the new area，the value of Outimage will be increased by 1，so the target quantities can be expressed by Outimage．

3）Using the method（2）to scan the current image and end the tag．The number and position of the head of each person were marked．The results of the tag are shown in Fig．5．

Fig．5 Tag results

3 Experimental simulation results analysis

In the transmission process，the clarity of the image might be reduced and the image could contain a lot of random noise after compression．The effect of traditional denosing method is poor．Therefore，we suggested a method to clear statistic of people number on the lift platform based on discrete wavelet transform algorithm，in which the discrete wavelet transform algorithm was used to deal with the noise and eliminate the noise to provide accurate number foundation for the extraction of workers contour features．The image pixels of the workers were calculated by computer vision image technology and the clear portrait was obtained，which can realize speed statistics of the number of workers on the lift platform．

In order to verify the superiority of the algorithm proposed in this paper，a simulation experiment was needed．Experiments were carried out by simulating the lift platform．Equipment used in the tests include：the types of ag-hp x 250 of the camera produced by Matsushita，digital image acquisition card MV-1394B produced by the Microvision production models．And test configuration of the computer in this test includes：Intel Pentium Dual Core E5300 2．6 GHz CPU，2G DDR3 memory．The image size is 320*240．When the test is fixed，the camera is placed in the appropriate height，and the area of the region is similar to the lift platform，and the image is processed by the time cut of every five frame．In the experiment，the images of the transmission of the traditional algorithm were compared．The results are shown in Fig．6．

Fig．6 Experimental contrast effect chart

Through the comparison of the images that the algorithm presented in this paper for image denoising processing can avoid the disadvantages of traditional image and can realize fast and accurate statistics of the number of workers on the platform lift．To analyze the experimental data，we summarized the following table：

Table 1 Comparison between the algorithm in this paper and the traditional algorithm

From the comparison of diagram and experimental comparison chart，we can see that this algorithm is very good to solve the noise problem and can clear and accurately have the number of workers statistical on lift platform，which avoids the disadvantage of traditional algorithm，that the resolution is not high，poor accuracy and drawbacks．In the case of the time consuming and the traditional algorithm，the accuracy of the statistic is greatly improved（95．3%）．The results show that the algorithm is of higher accuracy and has strong practicability．

4 Conclusions

This paper presented a statistical method for the people number counting of lift platforms based on computer visual images．Using discrete wavelet transform to denoise the image collection and improve the image definition，using Gaussian curve to calculate contour pixels one by one，we got a clear outline，and finally marked outline and count，and can have timely and accurate statistics on the number of workers on the platform lift to timely judge if the number of workers on lift platform is overloaded in order to protect the personal safety of workers，which is of high practical value．

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