CN110706177B - Method and system for equalizing gray level of side-scan sonar image - Google Patents
Method and system for equalizing gray level of side-scan sonar image Download PDFInfo
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Abstract
The invention discloses a method and a system for equalizing the gray level of a side-scan sonar image. The method comprises the following steps: carrying out geographic coding on the flight path data and the side-scan sonar waterfall layout to obtain a side-scan sonar image; dividing each side-scan sonar survey line image with geographic coordinates in the side-scan sonar image into a plurality of path buffer areas; the pixel points in the same path buffer area are positioned on the same side of the flight path line, and the distance between the pixel points and the flight path line is within a preset range; extracting the gray feature of each path buffer area, and carrying out gray equalization on pixel points in the path buffer areas according to the gray feature; and performing gap interpolation and image mosaic on all equalized side-scan sonar survey line images with geographic coordinates to obtain equalized side-scan sonar images. The invention performs gray scale equalization processing on the side-scan sonar image after the geocoding, can improve the side-scan sonar imaging quality, and further improves the subsequent image interpretation or automatic classification precision.
Description
Technical Field
The invention relates to the technical field of underwater landform measurement, in particular to a method and a system for equalizing the gray level of a side-scan sonar image.
Background
Side Scan Sonar (SSS) is also called "Side Scan Sonar", and is a geophysical prospecting technique for realizing imaging of submarine topography. The side scan sonar transmits a wave beam sector to the seabed in an oblique incidence mode, and seabed imaging is carried out by recording the arrival time and the intensity of echo signals.
The side scan sonar transducer continuously emits acoustic signals, records the received acoustic signals according to time sequence, and displays the received signals corresponding to each emission as a row of pixels according to a specific color mapping rule, which is called as a scanning line. The pixels are arranged line by line as the side scan sonar moves along the course, and the image thus constructed is called a "waterfall plot". As shown in fig. 1, each pixel position of the "waterfall graph" corresponds to the time when the echo arrives, and the gray level (or corresponding color) of the pixel corresponds to the intensity of the echo signal. Generally, a waterfall plot has 4 characteristic lines, namely a zero line, a sea line (when a side-scan sonar transducer side lobe is small, the sea line is not easy to appear), a sea bottom line and a scanning line.
According to the waterfall plot image obtained by the side-scan sonar, due to energy attenuation in the sound wave propagation process, the side-scan sonar image often has the situation that a near-field signal is strong and a far-field signal is weak, and the trend of the overall attenuation is generally nonlinear. The waterfall graph recorded by the side-scan sonar system does not generally contain explicit geographic coordinate information, and an original signal is gradually weakened from a zero-bit line from near to far, so that a landform image with the geographic coordinate information can be formed by preprocessing, and subsequent applications such as substrate classification are performed. The whole data processing process can be called as a preprocessing process before a complete image with space coordinate information is formed by the waterfall diagram acquired by the side scan sonar. The preprocessing of the side scan sonar image is mainly completed by adopting equipment such as a computer and a graphic workstation, some side scan sonar manufacturers provide special software for data recording and simple preprocessing, and some general software such as Triton Survey, OIC Clean sweet, Qinsy, EIVA, Caris HIPS and SIPS, HYPACKHysweet, Fledermaus and the like can also support the data preprocessing of various models of side scan sonars.
The preprocessing process of the existing side scan sonar image mainly comprises the following steps: gain equalization, skew correction, filtering and denoising, track, course and speed information extraction, geocoding, image interpolation and image mosaic. The single survey line side scan sonar image after waterfall plot processing and geocoding generally comprises a flight path line, a scanning imaging zone and an image background area. The scanning imaging bands are generally symmetrically distributed on the left side and the right side of the trajectory line, and the water bottom information is mainly presented through the image gray scale change of the area. When a plurality of scanning imaging bands are subjected to geocoding, gap difference and image mosaic, a complete side scan sonar image of a measuring area is obtained, as shown in fig. 2. As can be seen from FIG. 2, when the gray scale equalization processing result of a single survey line side scan sonar image is not good, the side scan sonar image subjected to image mosaic can show obvious splicing traces, and the imaging effect and the subsequent application based on the image are seriously influenced. Therefore, in order to obtain a side-scan sonar image with uniform signal intensity, accurately interpret a water-bottom target displayed in the image, or automatically classify the substrate, the equalization of the side-scan sonar image is required.
At present, the gray level equalization of the side scan sonar image is mainly realized at two levels. One is a gain correction method of signal layer to realize gain modulation, so as to achieve the purpose of gray level equalization after image formation. And secondly, a gray level histogram normalization method of the waterfall layout layer realizes gray level equalization by utilizing the statistical characteristics of the side scan sonar waterfall layout. The gain correction method of the signal layer is based on a physical model of sound wave propagation in water, and is the basis of gray level equalization correction, but the imaging effect is often difficult to achieve the expectation; the gray level histogram normalization method of the waterfall layout level is based on the statistical characteristics of a section of continuous measurement signals, and compared with the first method, the method has certain improvement on the image forming effect, but because each pixel of the waterfall layout does not directly contain space coordinate information, the method is only suitable for gray level correction of local images, and the side scan sonar image forming quality still needs to be improved.
Disclosure of Invention
Therefore, it is necessary to provide a method and a system for equalizing the gray scale of a side-scan sonar image, so as to improve the quality of a side-scan sonar image, and further improve the accuracy of subsequent image interpretation or automatic classification.
In order to achieve the purpose, the invention provides the following scheme:
a side scan sonar image gray level equalization method comprises the following steps:
acquiring flight path line data and a side scan sonar waterfall layout;
carrying out geographic coding on the flight path data and the side-scan sonar waterfall layout to obtain a side-scan sonar image; the side-scan sonar images comprise side-scan sonar survey line images with multiple geographical coordinates; the central line of each side-scan sonar survey line image with the geographic coordinates is a corresponding trajectory line; the navigation track line divides the side scan sonar survey line image with the geographic coordinates into a left side and a right side;
dividing each side-scan sonar survey line image with the geographic coordinates in the side-scan sonar image into a plurality of path buffer areas; the pixel points in the same path buffer area are positioned on the same side of the flight path line, and the distance between the pixel points and the flight path line is within a preset range; the preset ranges corresponding to different path buffer areas positioned on the same side of the flight path line are not overlapped; the preset ranges corresponding to any two adjacent path buffer areas form a continuous interval;
extracting the gray features of each path buffer area, and carrying out gray equalization on pixel points in the path buffer areas according to the gray features to obtain equalized side scan sonar survey line images with geographic coordinates;
and performing gap interpolation and image mosaic on all the equalized side-scan sonar survey line images with geographic coordinates to obtain equalized side-scan sonar images.
Optionally, the extracting of the grayscale characteristics of each path buffer area, and according to the grayscale characteristics, performing grayscale equalization on the pixels in the path buffer area to obtain an equalized side-scan sonar survey line image with geographic coordinates specifically includes:
counting gray values of pixel points in each path buffer area;
establishing a gray level histogram corresponding to each path buffer area according to the gray level value;
calculating the median of each gray level histogram;
and carrying out gray level equalization on the pixel points in the path buffer area according to the median to obtain an equalized side-scan sonar survey line image with geographic coordinates.
Optionally, the gray level equalization is performed on the pixel points in the path buffer area according to the median, so as to obtain an equalized side-scan sonar survey line image with geographic coordinates, specifically:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijAnd expressing the pixel value of the j th pixel point in the ith path buffer area after equalization.
Optionally, the gray level equalization is performed on the pixel points in the path buffer area according to the median, so as to obtain an equalized side-scan sonar survey line image with geographic coordinates, specifically:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijAnd expressing the pixel value of the j th pixel point in the ith path buffer area after equalization.
The invention also provides a side scan sonar image gray scale equalization system, which comprises:
the image acquisition module is used for acquiring flight path line data and a side scan sonar waterfall layout;
the geocoding module is used for geocoding the trajectory data and the side-scan sonar waterfall map to obtain a side-scan sonar image; the side-scan sonar images comprise side-scan sonar survey line images with multiple geographical coordinates; the central line of each side-scan sonar survey line image with the geographic coordinates is a corresponding trajectory line; the navigation track line divides the side scan sonar survey line image with the geographic coordinates into a left side and a right side;
the path buffer area dividing module is used for dividing each side-scan sonar survey line image with the geographic coordinates in the side-scan sonar images into a plurality of path buffer areas; the pixel points in the same path buffer area are positioned on the same side of the flight path line, and the distance between the pixel points and the flight path line is within a preset range; the preset ranges corresponding to different path buffer areas positioned on the same side of the flight path line are not overlapped; the preset ranges corresponding to any two adjacent path buffer areas form a continuous interval;
the gray level equalization module is used for extracting the gray level characteristics of each path buffer area and carrying out gray level equalization on the pixel points in the path buffer areas according to the gray level characteristics to obtain an equalized side scan sonar survey line image with geographic coordinates;
and the image mosaic module is used for carrying out gap interpolation and image mosaic on all the equalized side-scan sonar survey line images with geographic coordinates to obtain equalized side-scan sonar images.
Optionally, the gray scale equalization module specifically includes:
the gray value counting unit is used for counting the gray values of the pixel points in the path buffers;
the gray histogram establishing unit is used for establishing a gray histogram corresponding to each path buffer area according to the gray value;
a median calculating unit for calculating the median of each gray level histogram;
and the equalization unit is used for carrying out gray level equalization on the pixel points in the path buffer area according to the median to obtain an equalized side scan sonar survey line image with the geographic coordinates.
Optionally, the equalization unit includes a first equalization subunit;
the first equalization subunit specifically includes:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijAnd expressing the pixel value of the j th pixel point in the ith path buffer area after equalization.
Optionally, the equalization unit includes a second equalization subunit;
the second equalization subunit specifically includes:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijAnd expressing the pixel value of the j th pixel point in the ith path buffer area after equalization.
Compared with the prior art, the invention has the beneficial effects that:
compared with the prior art in which processing is directly performed on a waterfall plot, the method and the system for equalizing the gray scale of the side-scan sonar image provided by the invention adopt the gray scale equalization optimization processing method based on the side-scan sonar image after geographic coding, and eliminate obvious splicing traces in the image after being embedded due to uneven gray scale after splicing a plurality of survey line images, thereby improving the quality of the side-scan sonar imaging and further improving the efficiency and precision of subsequent image interpretation or automatic classification.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a side scan sonar waterfall plot;
FIG. 2 is a complete side scan sonar image of the measurement zone;
FIG. 3 is a flowchart of a method for equalizing the gray level of a side-scan sonar image according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a side scan sonar survey image with geographic coordinates before and after path buffer division according to an embodiment of the present invention;
FIG. 5 is a gray value statistical graph of pixel points in the path buffer areas on both sides of the side scan sonar survey line image with geographic coordinates according to the embodiment of the present invention;
FIG. 6 is a gray value statistical graph of pixel points in the path buffer areas on both sides of the side-scan sonar ranging image with geographic coordinates after being equalized by a ratio method according to the embodiment of the present invention;
FIG. 7 is a gray value statistical graph of pixel points in the path buffer areas on both sides of the side-scan sonar ranging image with geographic coordinates after being equalized by an absolute value method according to the embodiment of the present invention;
FIG. 8 is a comparison of the effects of several gray scale equalization methods;
FIG. 9 is a comparison graph of several gray scale equalization K-Means classification results;
fig. 10 is a schematic structural diagram of a side-scan sonar image gray scale equalization system according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 3 is a flowchart of a side-scan sonar image gray scale equalization method according to an embodiment of the present invention.
Referring to fig. 3, the method for equalizing the gray scale of the side-scan sonar image according to the embodiment includes:
step S1: and acquiring flight path data and a side-scan sonar waterfall diagram.
Step S2: and carrying out geographic coding on the flight path data and the side-scan sonar waterfall layout to obtain a side-scan sonar image.
The side-scan sonar images comprise side-scan sonar survey images with multiple geographic coordinates; the central line of each side-scan sonar survey line image with the geographic coordinates is a corresponding trajectory line; the navigation track divides the side scan sonar survey image with geographic coordinates into the left side and the right side.
The geocoding in the step is that according to the flight path data recorded during the measurement of the side scan sonar, the geographic coordinate corresponding to each pixel in the side scan sonar waterfall layout is calculated by using the existing software, and then the gray value of each pixel is mapped to the plane image with the geographic coordinate, so that the side scan sonar survey line image with a plurality of geographic coordinates is obtained. The flight path data is the centroid geographical coordinates of the side-scan sonar transducer at each moment recorded by the GPS in the measurement process. Geocoding can be implemented by using software such as Triton Survey, OIC Clean sweet, Qinsy, EIVA, Caris HIPS and SIPS, HYPACK Hysweet, Fladermaus and the like.
Step S3: dividing each side-scan sonar survey line image with geographic coordinates in the side-scan sonar image into a plurality of path buffer areas; the pixel points in the same path buffer area are positioned on the same side of the flight path line, and the distance between the pixel points and the flight path line is within a preset range; the preset ranges corresponding to different path buffer zones positioned on the same side of the flight path line are not overlapped; the preset ranges corresponding to any two adjacent path buffers form a continuous interval.
The method comprises the following steps: and dividing a path buffer area (buffer) according to the distance from each point on the side-scan sonar single-line image with the geographic coordinates to a trajectory line (sonar path). The sonar path is a sonar track recorded by a Global Positioning System (GPS) when side-scan sonar is measured, corresponds to a side-scan sonar single-line image with geographic coordinates, and is usually at the central line of the side-scan sonar single-line image with geographic coordinates, so that the sonar path can be manually drawn according to the side-scan sonar image, as shown in part (a) of FIG. 4, namely, the sonar path is represented, the scanning zone is represented, namely, an area to be subjected to gray level equalization, and the background area is represented, namely, an area not to be processed. The path buffer zone is a plurality of areas with equal width in a certain width range at two sides of the sonar path, is called as a buffer zone, and belongs to the characteristics of pixels in the same buffer zone: the distance from each pixel to the sonar path line is close. The division of the buffers follows the principle of no overlap and no gaps. Depending on the purpose of the sonar image application, it is generally recommended that the width of the buffer be 0.1-0.3 times the minimum target diameter to be identified, or 8-10 pixels wide. Based on the law of correlation between the gray level of the side-scan sonar image and the reflection distance, when the width of the buffer area is selected appropriately, the gray level of the pixel in each buffer area is approximately considered to be close to obey the same normal distribution function, while the gray levels of the pixels in two adjacent buffer areas have a certain difference and obey the normal distribution functions with different mean values and variances, as shown in part (b) of fig. 4.
Step S4: and extracting the gray features of each path buffer area, and carrying out gray equalization on the pixel points in the path buffer areas according to the gray features to obtain the equalized side-scan sonar survey line image with the geographic coordinates.
The step S4 specifically includes:
1) counting gray values of pixel points in each path buffer area; establishing a gray level histogram corresponding to each path buffer area according to the gray level value; 2) calculating the median of each gray level histogram; 3) and carrying out gray level equalization on the pixel points in the path buffer area according to the median to obtain an equalized side-scan sonar survey line image with the geographic coordinates. Fig. 5 is a gray scale value statistical graph of pixel points in path buffer areas on both sides of a side scan sonar survey line image with geographic coordinates according to an embodiment of the present invention, where part (a) of fig. 5 is a gray scale value statistical graph of pixel points in 70 path buffer areas on one side when the width of the path buffer area on one side is 8 pixels, and part (b) of fig. 5 is a gray scale value statistical graph of pixel points in 70 path buffer areas on the other side when the width of the path buffer area on the other side is 8 pixels. Referring to fig. 5, the path buffers are arranged in proximity to the flight path, the box-shaped regions represent gray scale intervals in which most of the pixels (about 90% of the number of pixels in the buffer) have gray scale values, the "+" sign represents the gray scale distribution of a few pixel values, and the few pixel values represented by the "+" sign are generally considered to be outliers due to noise. According to the statistical result, the general change trends of the gray scale values of the scanning imaging bands on the left side and the right side are basically consistent, and the rule that the average value and the variance of the gray scale values in the buffer band are gradually reduced the farther the distance from the flight path line is presented. In the figure, the sum of the widths of the generated buffer areas is slightly larger than the width of the whole scan imaging band, so that after the buffer area reaches the 53 th bar, the gray median of the pixels in the image is 0, which indicates that the buffer area generated later exceeds the scan imaging band range and reaches the background area of the image.
Gray level equalization is carried out on pixel points in the path buffer area according to the median in the step 3), and the equalized side-scan sonar survey line image with the geographic coordinates is obtained, so that the gray level of each sonar image can be adaptively equalized (the left side and the right side do not need to be distinguished), and the deviation caused by unreasonable parameter setting when the TVG function is manually set is avoided. Specifically, two methods can be adopted for implementation.
A ratio method is adopted, and specifically comprises the following steps:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijIndicating the pixel value of the jth pixel point in the ith path buffer，Xi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of a side-scan sonar survey image with geographic coordinates, e.g., 256 gray scales for a side-scan sonar survey image, HmaxCan take 256, HijExpressing the pixel value of the j pixel point in the ith path buffer area after equalization due to XijAlways non-negative, and therefore has HijIs more than or equal to 0. Fig. 6 is a gray value statistical graph of pixel points in the path buffer areas on both sides of the side scan sonar ranging image with geographic coordinates after being equalized by a ratio method in the embodiment of the present invention. Referring to fig. 6, the gray scale equalization by the ratio method corresponds to the linear stretching of the histogram, and gradually adjusts the pixel gray scales in the corresponding regions to a predetermined range, so that the average and variance of the pixel gray scales in each buffer area on both the left side (part (a) of fig. 6) and the right side (part (b) of fig. 6) are substantially uniform, and the normal distribution characteristics of the pixel gray scale values in each buffer area can be maintained.
Secondly, an absolute value method is adopted, and the method specifically comprises the following steps:
Step S5: and performing gap interpolation and image mosaic on all equalized side-scan sonar survey line images with geographic coordinates to obtain equalized side-scan sonar images.
In this step, "gap interpolation" and "image mosaic" operations can be performed using existing software tools. The gap interpolation is to fill up the vacant pixel gray value in the middle area uncovered by a plurality of side scan sonar scanning ranges by adopting a data interpolation algorithm (such as a nearest neighbor method, a spline interpolation method, a geographical weighting method and the like) so as to ensure the integrity of the whole scanning range. And image mosaic is to superpose the image positions of the equalized side-scan sonar survey images with geographic coordinates to obtain a complete side-scan sonar image of the whole area.
As an alternative embodiment, after the side-scan sonar waterfall graph is acquired in step S1, the side-scan sonar waterfall graph is further preprocessed, where the preprocessing includes gain equalization, slant correction, and filtering elimination. Specifically, software such as Triton Survey, OIC Clean Sweep, Qinsy, EIVA, Caris HIPS and SIPS, HYPACKHysweep, Fledermaus and the like can be used for preprocessing the side scan sonar waterfall diagram. After the pretreatment is finished, the operations of steps S2-S5 are performed on the basis of the pretreatment.
The effectiveness of the above-described side-scan sonar image gray scale equalization method is verified below.
The side-scan sonar image gray scale equalization method of the embodiment is a gray scale equalization optimization processing method of a side-scan sonar image after geographic coding, and can eliminate obvious splicing traces in an image after being embedded due to uneven gray scales after splicing of a plurality of survey line images, so that the side-scan sonar imaging quality is improved, and the subsequent image interpretation or automatic classification efficiency and precision are improved. The effect is exemplified as follows:
selecting 6 side scan sonar scanning survey line data of an experimental area in the east China sea to perform gray level equalization treatment, wherein the original image scanning area contains uniform sandy substrate, a small amount of gravel, reef and other targets, and comparing the two methods with images generated by Triton Isis software manual TVG correction and automatic TVG correction.
(1) And (5) visual effect. As shown in fig. 8, the gray level equalization by the ratio method (part (c) of fig. 8) and the absolute value method (part (d) of fig. 8) proposed by the present invention has a significant effect in eliminating the gray level non-uniformity of each scan band, and is better than the method of manually setting TVG parameters (part (a) of fig. 8), and a complete image with uniform and consistent overall gray level is obtained; the method is superior to the automatic TVG correction effect (part (b) of fig. 8)) in terms of information retention of the target, clear target edge information is displayed, and relative difference between the target and background gray values is maintained, so that manual identification of the underwater target is facilitated. Compared with the gray level equalization effect of the absolute value method, the gray level equalization method has the advantages that the image with more uniform gray level can be obtained by the specific value method, and the visual effect of the image is improved.
(2) And (5) classifying effect. 4 groups of results shown in FIG. 9 are classified based on image gray scale by using the K-means unsupervised classification function of the ENVI 5.0 software, and the results are shown in FIG. 9. The images processed based on the ratio method (part (c) of fig. 9) and the absolute value method (part (d) of fig. 9) provided by the invention significantly weaken the influence of the uneven gray scale of the scanning band on the classification of the substrate (part (a) of fig. 9 and part (b) of fig. 9), and the classification results corresponding to the ratio method and the absolute value method show that the absolute value method highlights the details of the submarine target in the image and is more beneficial to the classification and identification of the target in the image.
The invention also provides a side-scan sonar image gray scale equalization system, and fig. 10 is a schematic structural diagram of the side-scan sonar image gray scale equalization system according to the embodiment of the invention. Referring to fig. 10, the side-scan sonar image gray-scale equalization system includes:
and the image acquisition module 101 is used for acquiring flight path line data and a side scan sonar waterfall layout.
The geocoding module 102 is used for geocoding the trajectory data and the side-scan sonar waterfall map to obtain a side-scan sonar image; the side-scan sonar images comprise side-scan sonar survey images with multiple geographic coordinates; the central line of each side-scan sonar survey line image with the geographic coordinates is a corresponding trajectory line; the navigation track divides the side scan sonar survey image with geographic coordinates into the left side and the right side.
The path buffer area dividing module 103 is used for dividing each side-scan sonar survey line image with geographic coordinates in the side-scan sonar image into a plurality of path buffer areas; the pixel points in the same path buffer area are positioned on the same side of the flight path line, and the distance between the pixel points and the flight path line is within a preset range; the preset ranges corresponding to different path buffer zones positioned on the same side of the flight path line are not overlapped; the preset ranges corresponding to any two adjacent path buffers form a continuous interval.
And the gray level equalization module 104 is configured to extract gray level features of each path buffer area, and perform gray level equalization on the pixel points in the path buffer areas according to the gray level features to obtain an equalized side scan sonar survey line image with geographic coordinates.
And the image mosaic module 105 is used for performing gap interpolation and image mosaic on all the equalized side-scan sonar survey line images with geographic coordinates to obtain equalized side-scan sonar images.
As an optional implementation manner, the gray scale equalization module 104 specifically includes:
and the gray value counting unit is used for counting the gray values of the pixel points in the path buffers.
And the gray histogram establishing unit is used for establishing a gray histogram corresponding to each path buffer area according to the gray value.
And the median calculating unit is used for calculating the median of each gray level histogram.
And the equalization unit is used for carrying out gray level equalization on the pixel points in the path buffer area according to the median to obtain an equalized side-scan sonar survey line image with geographic coordinates.
As an alternative embodiment, the equalization unit includes a first equalization subunit; the first equalization subunit specifically includes:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijAnd expressing the pixel value of the j th pixel point in the ith path buffer area after equalization.
As an alternative embodiment, the equalization unit comprises a second equalization subunit; the second equalization subunit specifically includes:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijAnd expressing the pixel value of the j th pixel point in the ith path buffer area after equalization.
For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (2)
1. A side scan sonar image gray level equalization method is characterized by comprising the following steps:
acquiring flight path line data and a side scan sonar waterfall layout;
carrying out geographic coding on the flight path data and the side-scan sonar waterfall layout to obtain a side-scan sonar image; the side-scan sonar images comprise side-scan sonar survey line images with multiple geographical coordinates; the central line of each side-scan sonar survey line image with the geographic coordinates is a corresponding trajectory line; the navigation track line divides the side scan sonar survey line image with the geographic coordinates into a left side and a right side;
dividing each side-scan sonar survey line image with the geographic coordinates in the side-scan sonar image into a plurality of path buffer areas; the pixel points in the same path buffer area are positioned on the same side of the flight path line, and the distance between the pixel points and the flight path line is within a preset range; the preset ranges corresponding to different path buffer areas positioned on the same side of the flight path line are not overlapped; the preset ranges corresponding to any two adjacent path buffer areas form a continuous interval;
extracting the gray features of each path buffer area, and carrying out gray equalization on pixel points in the path buffer areas according to the gray features to obtain equalized side scan sonar survey line images with geographic coordinates;
performing gap interpolation and image mosaic on all the equalized side-scan sonar survey line images with geographic coordinates to obtain equalized side-scan sonar images;
the method comprises the following steps of extracting the gray features of each path buffer area, carrying out gray equalization on pixel points in the path buffer areas according to the gray features, and obtaining equalized side-scan sonar survey line images with geographic coordinates, and specifically comprises the following steps:
counting gray values of pixel points in each path buffer area;
establishing a gray level histogram corresponding to each path buffer area according to the gray level value;
calculating the median of each gray level histogram;
carrying out gray level equalization on the pixel points in the path buffer area according to the median to obtain an equalized side-scan sonar survey line image with geographic coordinates;
the method comprises the following steps of carrying out gray level equalization on pixel points in a path buffer area according to the median to obtain an equalized side-scan sonar survey line image with geographic coordinates, and specifically comprises the following steps:
wherein i represents the number of the path buffer, and j represents the pairNumber of pixels in the response path buffer, XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijExpressing the pixel value of the j pixel point in the ith path buffer area after equalization;
or, the gray level equalization is performed on the pixel points in the path buffer area according to the median, so as to obtain an equalized side-scan sonar survey line image with geographic coordinates, specifically:
2. a side scan sonar image gray scale equalization system is characterized by comprising:
the image acquisition module is used for acquiring flight path line data and a side scan sonar waterfall layout;
the geocoding module is used for geocoding the trajectory data and the side-scan sonar waterfall map to obtain a side-scan sonar image; the side-scan sonar images comprise side-scan sonar survey line images with multiple geographical coordinates; the central line of each side-scan sonar survey line image with the geographic coordinates is a corresponding trajectory line; the navigation track line divides the side scan sonar survey line image with the geographic coordinates into a left side and a right side;
the path buffer area dividing module is used for dividing each side-scan sonar survey line image with the geographic coordinates in the side-scan sonar images into a plurality of path buffer areas; the pixel points in the same path buffer area are positioned on the same side of the flight path line, and the distance between the pixel points and the flight path line is within a preset range; the preset ranges corresponding to different path buffer areas positioned on the same side of the flight path line are not overlapped; the preset ranges corresponding to any two adjacent path buffer areas form a continuous interval;
the gray level equalization module is used for extracting the gray level characteristics of each path buffer area and carrying out gray level equalization on the pixel points in the path buffer areas according to the gray level characteristics to obtain an equalized side scan sonar survey line image with geographic coordinates;
the image mosaic module is used for carrying out gap interpolation and image mosaic on all the equalized side-scan sonar survey line images with geographic coordinates to obtain equalized side-scan sonar images;
the gray scale equalization module specifically comprises:
the gray value counting unit is used for counting the gray values of the pixel points in the path buffers;
the gray histogram establishing unit is used for establishing a gray histogram corresponding to each path buffer area according to the gray value;
a median calculating unit for calculating the median of each gray level histogram;
the equalization unit is used for carrying out gray level equalization on the pixel points in the path buffer area according to the median to obtain an equalized side scan sonar survey line image with geographic coordinates;
the equalization unit comprises a first equalization subunit;
the first equalization subunit specifically includes:
wherein i represents the number of the path buffer, j represents the number of the pixel point in the corresponding path buffer, and XijRepresents the pixel value, X, of the jth pixel point in the ith path bufferi,medianRepresenting the median of the gray values of all the pixels in the ith path buffer, HmaxRepresenting the maximum value of the gray scale of the side-scan sonar survey image with geographic coordinates, HijExpressing the pixel value of the j pixel point in the ith path buffer area after equalization;
or, the equalization unit comprises a second equalization subunit;
the second equalization subunit specifically includes:
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