CN105847708B - Line-scan digital camera automatic exposure method of adjustment based on image histogram analysis and system - Google Patents

Abstract

The present invention provides an automatic exposure adjustment method and system for line array cameras based on image histogram analysis, including calculating the gray histogram of the current image, normalizing the gray histogram, and obtaining the left boundary of the histogram of the current image , right boundary and peak value; calculate the camera exposure adjustment value according to the expected peak value of the grayscale histogram of the image; if the absolute value of the camera exposure adjustment value is greater than or equal to the adjustment threshold value, the new current exposure value is calculated, and the absolute value is less than the adjustment threshold value. Adjust to maintain the current exposure value, take pictures according to the current exposure value, and continue to adjust after obtaining a new image as the current image. The present invention performs histogram analysis on acquired image data, utilizes expected image quality and its histogram distribution characteristics to adjust camera exposure time, and achieves the effect of camera automatically adjusting exposure time.

Description

Method and system for automatic exposure adjustment of line scan camera based on image histogram analysis

technical field

The invention relates to the field of digital image processing, in particular to an automatic exposure adjustment method and system for a line array camera based on image histogram analysis.

Background technique

For imaging of moving targets (such as trains) in the field, taking into account the factors of movement and stitching, line array cameras are often used to take pictures. Compared with the environment of field image data collection, the supplementary light of active light sources is a necessary condition for taking pictures, but how to effectively eliminate the interference of external environment changes, such as night, sunny days, cloudy and rainy days, direct sunlight, and sports , to obtain a better image effect is a problem that must be solved. Image histogram analysis is usually used for statistical analysis of images and can be used for equalization (such as "a histogram equalization method for infrared images" (CN 104252700A), but there are few methods for reverse guidance and adjustment of camera exposure parameters.

To measure changes in external ambient light by means of photometry equipment, light intensity measurement, etc., factors such as shadow areas, external light source interference, and object movement need to be considered, as well as reflections on the imaging object itself. Currently, there is no good solution. Method. Therefore, it is necessary to provide a new camera exposure method to automatically adjust, so as to facilitate the acquisition of dynamic scene pictures with suitable brightness and clear imaging effect.

Contents of the invention

In order to solve the above problems, the present invention proposes an automatic exposure adjustment method and system for line scan cameras based on image histogram analysis. From the perspective of imaging quality analysis, external interference factors are reflected in the imaging results, and the current environment and the exposure time at the current moment to obtain high-quality images.

The technical solution of the present invention provides a method for automatically adjusting the exposure of a line-scan camera based on image histogram analysis, which is characterized in that it comprises the following steps:

Step 1, obtain the current image, calculate the grayscale histogram of the current image, normalize the grayscale histogram, and obtain the left boundary Left_Pos, right boundary Rigt_Pos and peak value of the histogram of the current image;

Step 2. Calculate the camera exposure adjustment value CExp according to the expected peak value Exp_Bright of the image gray histogram as follows,

Among them, Exp_Bright is the expected peak value of the image histogram, Left_Sec_Pos and Rigt_Sec_Pos are the secondary boundary values after removing the boundary peak value, and the correction coefficients k1 and k2 are the linear transformation coefficients of the image histogram;

Step 3. Compare the absolute value of the camera exposure adjustment value CExp with the preset adjustment threshold. If the absolute value of the camera exposure adjustment value CExp is greater than or equal to the adjustment threshold, add the camera exposure adjustment value and the current exposure value to obtain a new current exposure value, go to step 4; if the absolute value of the camera exposure adjustment value CExp is less than the adjustment threshold, no adjustment will be made, and the current exposure value will be kept, and go to step 4;

Step 4. Take pictures according to the current exposure value. After obtaining a new image as the current image, return to step 1 and continue to adjust.

Moreover, the histogram is intercepted according to the preset filtering threshold, and the left boundary Left_Pos, the right boundary Rigt_Pos and the peak value of the histogram of the current image are updated.

Moreover, the number of rows of the current image adopts a preset value m.

Also, m=1000.

Moreover, according to the preset value n, n>1, when taking pictures according to the current exposure value in step 4, it is to wait for (n-1)×m lines to be taken before extracting the latest m lines of images as the new current image, and then Go back to step 1 and continue to adjust.

The present invention also correspondingly provides an automatic exposure adjustment system for line array cameras based on image histogram analysis, including the following modules:

The first module is used to obtain the current image, calculate the gray histogram of the current image, normalize the gray histogram, and obtain the left boundary Left_Pos, the right boundary Rigt_Pos and the peak value of the histogram of the current image;

The second module is used to calculate the camera exposure adjustment value CExp according to the expected peak value Exp_Bright of the image grayscale histogram as follows,

Among them, Exp_Bright is the expected peak value of the image histogram, Left_Sec_Pos and Rigt_Sec_Pos are the secondary boundary values after removing the boundary peak value, and the correction coefficients k1 and k2 are the linear transformation coefficients of the image histogram;

The third module is used to compare the absolute value of the camera exposure adjustment value CExp with the preset adjustment threshold. If the absolute value of the camera exposure adjustment value CExp is greater than or equal to the adjustment threshold, add the camera exposure adjustment value and the current exposure value to obtain a new If the absolute value of the camera exposure adjustment value CExp is less than the adjustment threshold, no adjustment is made, the current exposure value is maintained, and the fourth module is ordered to work;

The fourth module is used to take pictures according to the current exposure value, and after obtaining a new image as the current image, order the first module to work and continue to adjust.

Moreover, the histogram is intercepted according to the preset filtering threshold, and the left boundary Left_Pos, the right boundary Rigt_Pos and the peak value of the histogram of the current image are updated.

Moreover, the number of rows of the current image adopts a preset value m.

Also, m=1000.

Moreover, according to the preset value n, n>1, when taking pictures according to the current exposure value in the fourth module, it is to wait for shooting (n-1)×m lines before extracting the latest m lines of images as the new current image, Then order the first module to work and continue to adjust.

The present invention conducts histogram analysis on the acquired image data, utilizes the change of the peak position and the change of the waveform characteristics of the histogram, and constructs the corresponding relationship between the exposure time and the peak value change, thereby using the desired image quality and its histogram distribution characteristics to expose the camera Time adjustment, so that the histogram characteristics of the obtained image data match the expected value, so as to achieve the effect of the camera automatically adjusting the exposure time.

Description of drawings

Fig. 1 is the application system architecture diagram of the embodiment of the present invention;

Fig. 2 is an image histogram obtained before adjustment according to an embodiment of the present invention.

Fig. 3 is a histogram of corresponding images acquired after adjustment according to an embodiment of the present invention.

Specific implementation method

In order to make it easier for those skilled in the art to understand and implement the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

An embodiment of the present invention provides an automatic exposure adjustment method for a line scan camera based on image histogram analysis, comprising the following steps:

Step 1, obtain the current image, calculate the grayscale histogram of the current image, normalize the grayscale histogram, and obtain the left boundary, right boundary and peak value of the histogram of the current image;

Embodiment In step 1, the grayscale histogram of the current image is normalized. In order to weaken the noise interference, the filter threshold k=0.3 of the histogram is set in the embodiment, and the histogram is intercepted to obtain the grayscale of the current image. Histogram new left boundary Left_Pos, right boundary Rigt_Pos and peak value. During specific implementation, those skilled in the art can preset filtering thresholds by themselves, and using empirical values can weaken the influence of noise.

Step 2. Calculate the camera exposure adjustment value according to the expected peak value of the image gray histogram;

In step 2, if the left boundary Left_Pos=0 or the right boundary Rigt_Pos=255, then calculate the cumulative distribution of the image between the new left and right peaks, so as to achieve histogram equalization and obtain the left of the new histogram Boundary Left_Sec_Pos, Right Boundary Rigt_Sec_Pos.

In the embodiment, the expected peak parameter Exp_Bright of the ideal image histogram is input, and the camera exposure adjustment value CExp is calculated according to the formula:

Among them, Exp_Bright is the expected peak of the image histogram, and Left_Sec_Pos and Rigt_Sec_Pos are the secondary boundary values after removing the boundary peak. Among them, the correction coefficients k1 and k2 are linear transformation coefficients of the image histogram, and those skilled in the art can preset the values by themselves during specific embodiments, for example, they can be obtained by changing the exposure time of the camera in a fixed environment to obtain the average gray value of the standard image. , the embodiment takes k1=5, k2=6.

Step 3. In order to ensure the efficiency of system adjustment, during specific implementation, those skilled in the art can preset the adjustment threshold by themselves. The larger the value, the higher the efficiency and the lower the adjustment accuracy. The smaller the value, the lower the adjustment efficiency and the adjustment accuracy. higher. The embodiment sets the adjustment threshold to 10, that is, the absolute value of the camera exposure adjustment value is greater than or equal to 10, indicating that the effect is not satisfactory. Add the camera exposure adjustment value and the current exposure value to obtain a new current exposure value, press the new current exposure value Value enters step 4 to take a photo. When a new image is obtained as the current image, it will return to step 1 and repeat step 1, step 2 and step 3 to continue adjustment; if the absolute value of the exposure adjustment value is less than 10, no adjustment is currently required. Make the camera adjustment value equal to zero, keep using the current exposure value, and go to step 4;

Step 4. According to the current exposure value, the camera normally takes pictures and acquires images.

In step 4, take photos according to the current camera exposure value, continue to take a new image as the current image, return to step 1, and continue to adjust, so as to achieve the purpose of continuously obtaining clear images. until the system stops working.

An example of the system architecture applying the technical solution of the present invention is shown in Figure 1. After capturing the image from the initial camera, the computer that executes the above process can monitor the image, adjust the camera parameters, and store it in the server. The server outputs the corresponding command to the industrial computer to control the image. Adjust the exposure value of the line scan camera. For example, it can be used for outdoor dynamic train monitoring to obtain clear images for subsequent vehicle monitoring and identification. Then, the main use environment is the outdoor environment, and the use conditions should adapt to various weather changes. In the specific implementation, a set of inverted "L"-shaped brackets can be used; an industrial camera that takes pictures vertically downward is installed on the horizontal bar of the inverted "L"-shaped bracket to take pictures of the top image, and an industrial camera that is vertical to the train running is installed on the vertical bar. Direction of the industrial camera, and add a number of supplementary light equipment, such as light source LED. After the hardware environment is deployed in place, the image collection can be carried out. After the first image is obtained by adopting the technical solution of the present invention, the exposure time is automatically adjusted according to the external environment to obtain an ideal image.

According to the characteristics of the line scan camera, during specific implementation, those skilled in the art can preset the image calculation unit by themselves, that is, the number of lines of the current image adopts the preset value m. This embodiment takes the initial 1000-line image as an image calculation unit, obtains its histogram information (as shown in Figure 2), combines the previous exposure time, obtains the exposure time adjustment value (as shown in Figure 3), and then performs the calculation on the exposure value of the camera The adjustment is also to obtain the adjusted 1000 rows of data. That is, the current image always takes m=1000 lines of image data.

During the adjustment process, the camera normally collects images. In order to avoid adjusting the exposure value too frequently, the present invention further proposes that no matter whether the new current exposure value or the original current exposure value is used to take pictures, it is not necessary to obtain a new image immediately. As the current image, the latest m-line image is extracted as the new current image after waiting for (n-1)×m lines to be captured. In the embodiment, the image performance is close to adjusting the exposure time for every n×1000 lines, wherein the n value can be set according to the required adjustment efficiency, n>1, and those skilled in the art can preset n by themselves during specific implementation. value of . In the embodiment, n=2, until the adjustment work is finished.

During specific implementation, the method provided by the present invention can realize the automatic operation process based on software technology, and can also realize the corresponding system in a modular manner.

The embodiment of the present invention also provides an automatic exposure adjustment system for line array cameras based on image histogram analysis, including the following modules:

The first module is used to obtain the current image, calculate the gray histogram of the current image, normalize the gray histogram, and obtain the left boundary Left_Pos, the right boundary Rigt_Pos and the peak value of the histogram of the current image;

The second module is used to calculate the camera exposure adjustment value CExp according to the expected peak value Exp_Bright of the image grayscale histogram as follows,

Among them, Exp_Bright is the expected peak value of the image histogram, Left_Sec_Pos and Rigt_Sec_Pos are the secondary boundary values after removing the boundary peak value, and the correction coefficients k1 and k2 are the linear transformation coefficients of the image histogram;

The third module is used to compare the absolute value of the camera exposure adjustment value CExp with the preset adjustment threshold. If the absolute value of the camera exposure adjustment value CExp is greater than or equal to the adjustment threshold, add the camera exposure adjustment value and the current exposure value to obtain a new If the absolute value of the camera exposure adjustment value CExp is less than the adjustment threshold, no adjustment is made, the current exposure value is maintained, and the fourth module is ordered to work;

The fourth module is used to take pictures according to the current exposure value, and after obtaining a new image as the current image, order the first module to work and continue to adjust.

For the specific implementation of each module, reference may be made to the corresponding steps, which will not be described in detail in the present invention.

The above descriptions are only used to illustrate the specific implementation cases of the present invention, and are not intended to limit the scope of the present invention. For example, all those skilled in the art have accomplished everything without departing from the spirit and principles indicated by the present invention. Effective changes or modifications should still be covered by the scope of the claims of the present invention.

Claims (10)

1. a kind of line-scan digital camera automatic exposure method of adjustment based on image histogram analysis, which is characterized in that including following step Suddenly：

Step 1 obtains present image, calculates the grey level histogram of present image, which is normalized, and obtains Left margin Left_Pos, right margin Rigt_Pos and the peak value of the grey level histogram of present image；

Step 2, the expectation peak E xp_Bright according to the grey level histogram of image, calculate camera exposure adjusted value CExp such as Under,

Wherein, Left_Sec_Pos and Rigt_Sec_Pos is the secondary boundary value rejected after the peak value of boundary, correction factor k1, k2 For the linear transform coefficient of the grey level histogram of image；

Step 3, the absolute value for comparing camera exposure adjusted value CExp and preset adjustment threshold value, if camera exposure adjusted value The absolute value of CExp is more than or equal to adjustment threshold value, and camera exposure adjusted value is added with current exposure value, obtains new current exposure Light value enters step 4；If the absolute value of camera exposure adjusted value CExp is less than adjustment, threshold value keeps working as without adjustment Prior exposure value, enters step 4；

Step 4 is taken pictures according to current exposure value, after obtaining new image as present image, returns to step 1, Continue to adjust.

2. the line-scan digital camera automatic exposure method of adjustment based on image histogram analysis, feature exist according to claim 1 In：According to preset filtering threshold, the grey level histogram of image is intercepted, updates a left side for the grey level histogram of present image Boundary Left_Pos, right margin Rigt_Pos and peak value.

3. the line-scan digital camera automatic exposure method of adjustment according to claim 1 or claim 2 based on image histogram analysis, feature It is：The line number of present image uses preset numerical value m.

4. the line-scan digital camera automatic exposure method of adjustment based on image histogram analysis, feature exist according to claim 3 In：M=1000.

5. the line-scan digital camera automatic exposure method of adjustment based on image histogram analysis, feature exist according to claim 3 In：According to preset numerical value n, n>1, when being taken pictures according to current exposure value in step 4, after (n-1) × m rows to be captured such as being Newest m rows image is just extracted as new present image, step 1 is then returned to, continues to adjust.

6. a kind of line-scan digital camera automatic exposure based on image histogram analysis adjusts system, which is characterized in that including with lower die Block：

First module calculates the grey level histogram of present image, normalizing is carried out to the grey level histogram for obtaining present image Change, obtains the left margin Left_Pos, right margin Rigt_Pos and peak value of the grey level histogram of present image；

Second module is used for the expectation peak E xp_Bright of the grey level histogram according to image, calculates camera exposure adjusted value CExp is as follows,

Wherein, Left_Sec_Pos and Rigt_Sec_Pos is the secondary boundary value rejected after the peak value of boundary, correction factor k1, k2 For the linear transform coefficient of the grey level histogram of image；

Third module, the absolute value for comparing camera exposure adjusted value CExp and preset adjustment threshold value, if camera exposure The absolute value of adjusted value CExp is more than or equal to adjustment threshold value, and camera exposure adjusted value is added with current exposure value, is obtained new Current exposure value, order the 4th module work；If the absolute value of camera exposure adjusted value CExp be less than adjustment threshold value, not into Row adjustment keeps current exposure value, order the 4th module work；

4th module, for being taken pictures according to current exposure value, after obtaining new image as present image, order first Module works, and continues to adjust.

7. the line-scan digital camera automatic exposure based on image histogram analysis adjusts system according to claim 6, feature exists In：According to preset filtering threshold, the grey level histogram of image is intercepted, updates a left side for the grey level histogram of present image Boundary Left_Pos, right margin Rigt_Pos and peak value.

8. the line-scan digital camera automatic exposure based on image histogram analysis described according to claim 6 or 7 adjusts system, feature It is：The line number of present image uses preset numerical value m.

9. the line-scan digital camera automatic exposure based on image histogram analysis adjusts system according to claim 8, feature exists In：M=1000.

10. the line-scan digital camera automatic exposure based on image histogram analysis adjusts system according to claim 8, feature exists In：According to preset numerical value n, n>1, (the n-1) × m to be captured such as it is when being taken pictures according to current exposure value in the 4th module Newest m rows image is just extracted after row as new present image, is then ordered the first module to work, is continued to adjust.