CN102937593A - Ceramic radome crack automatic detection method - Google Patents

Abstract

The invention relates to a ceramic radome crack automatic detection method. The method is characterized in that the detection is carried out with a transmission image processing method. The method comprises the specific steps that: (1) a radome transmission image is obtained; (2) the image is subjected to gray scale and contrast enhancement processing, such that a crack area is underlined; (3) a binarization treatment is carried out; (4) a median filtering noise removing treatment is carried out; (5) a crack framework abstraction treatment is carried out; and (6) a crack length statistic treatment is carried out. With the treatment process, ceramic radome tiny cracks can be detected. According to the invention, with the radome crack transmission image processing method, radome crack automatic detection is realized.

Description

Ceramic radome crackle automatic testing method

Technical field

The present invention relates to a kind of ceramic radome crackle automatic testing method, belong to technical field of nondestructive testing.

Background technology

Thin-walled ceramic radome production is by often there being crack defect, but in current thin-walled ceramic radome product detects, detection to crackle is just undertaken by the method for manual observation, and it is large that this measuring method detects error, can't guarantee the detection quality of product.

Summary of the invention

The purpose of this invention is to provide a kind ofly can overcome above-mentioned defect, detect accurately, ceramic radome crackle automatic testing method that efficiency is high.Its technical scheme is:

A kind of ceramic radome crackle automatic testing method, is characterized in that adopting the transmission image disposal route to detect, and concrete steps are: 1) the antenna house transmission image obtains; 2) gradation of image contrast enhancement processing, outstanding slit region; 3) binary conversion treatment; 4) medium filtering is removed noise processed; 5) the key extraction process of crackle; 6) each Crack length of statistical treatment, obtain the length value of each Crack.

Described ceramic radome crackle automatic testing method, in step 1), arrange light source in ceramic radome inside, at the outside ccd video camera that adopts of ceramic radome, automatically carries out image acquisition, obtains the gray scale transmission image of ceramic radome different parts.

Described ceramic radome crackle automatic testing method, step 2) in, for crack defect district and non-defect area contrast are increased, outstanding crack defect district, need to carry out contrast enhancement processing, and contrast enhancement processing is the gray-scale value according to each pixel in certain rule pointwise modification image, thereby change gradation of image dynamic range and contrast, if original image is f (x, y), the image after processing is g (x, y), contrast increases and can be expressed as:

g(x,y)＝T[f(x,y)]

In formula, T means the variation of the image corresponding pixel points grey scale mapping after original image and processing.

Described ceramic radome crackle automatic testing method, in step 3), detection for the ease of crack defect, crackle gray level and non-defect area gray level strictly need to be distinguished, binary conversion treatment is exactly that the gray level image that contrast is strengthened arranges a gray threshold S, the gray-scale value of each pixel on image and gray threshold are compared, and image is converted into the bianry image that only contains two gray levels the most at last:

$g(x,y)=\left\{\begin{array}{cc}255& f(x,y)\&GreaterEqual;S\\ 0& f(x,y)<S\end{array}\right.$

Wherein f (x, y) is original image, and g (x, y) is bianry image, and gray level " 255 " is non-defect area, and gray level " 0 " is the crack defect district, and gray threshold S adopts the iteration threshold method to try to achieve.

Described ceramic radome crackle automatic testing method, in step 4), in order to remove the noise in binary image, need to be removed noise processed, the medium filtering Denoising disposal is the nonlinear smoothing method that suppresses noise, effective impulse noise mitigation, good keep the edge information simultaneously, for given n number { a ₁, a ₂..., a _n, by their ordered arrangement by size, when n is odd number, the number that is positioned at centre position is called the intermediate value of this n number, and when n is even number, the mean value that is positioned at centre position two numbers is called the intermediate value of this n number, is designated as med[a ₁, a ₂..., a _n], to set the pixel neighborhood of a point in medium filtering, to this neighborhood, be all rank-ordered pixels in moving window, the gray-scale value by its gray scale intermediate value as processed pixel, array [x (i, j)] _{M * N}Through window, be A _nMedium filtering after, the output of pixel (i, j) is designated as:

$y(i,j)=\underset{A_n(i,j)}{\mathrm{med}}\left[x(i,j)\right]$

In formula, A _n(i, j) means the neighborhood of point (i, j), and it contains n pixel.

Described ceramic radome crackle automatic testing method, in step 5), the key extraction of crackle is to carry out corrosion treatment on the Width of crackle, until crack width only has a pixel unit, it has kept the topological property of crackle, and the process that the set A skeleton is turned to S (A) can be expressed as:

$S\left(A\right)=\underset{k=0}{\overset{K}{\mathrm{\&cup;}}}{S}_k\left(A\right)$

And

In formula, B is structural element,

Continuous k the corrosion of expression to A.K is the number of times that A is etched into the front last iteration of empty set.

Described ceramic radome crackle automatic testing method, in step 6), for every Crack crack length statistics wherein, be that the crackle that the backbone has been changed is traveled through since an end, after the whole crackle of traversal, the length of crackle has just come out, wherein the statistics of length comprises two kinds of situations, it between pixel, is the upper and lower, left and right four direction of mode arranged side by side, distance between this pixel arranged side by side is 1 pixel, vergence direction has upper left, lower-left, upper right, bottom right four direction, and the distance between vergence direction is like this

Individual pixel will, according to the connected mode between pixel, be calculated respectively distance when measuring.

Compared with prior art, its advantage is in the present invention: adopted image to process automatic testing method the crackle of ceramic radome is detected, measurement result is more accurate, objective.

Embodiment

Inside at ceramic radome arranges light source, then, at the outside transmission image that adopts ccd video camera automatically to gather the antenna house different parts of antenna house, the gray level image gathered is processed according to following steps:

Step 1): for the crack defect district in the gray level image that makes to collect and the increase of non-defect area contrast and outstanding crack defect district, need to carry out contrast enhancement processing, adopt piecewise linearity to change and is processed, transformation for mula is:

$g(x,y)=\left\{\begin{array}{cc}\frac{c}{a}\&times;f(x,y)& [0,a)\\ \frac{d-c}{b-a}\&times;(f(x,y)-a)+c& [a,b]\\ \frac{255-d}{255-b}\&times;(f(x,y)-b)+d& (b,255]\end{array}\right.$

Wherein f (x, y) means the gray level image collected, and g (x, y) means the image that contrast strengthens, and waypoint is elected as according to the grey value profile situation of the image obtained: a=70, b=170, c=30, d=110.

Step 2): step 1) is processed to the gray level image obtained a gray threshold is set, the gray-scale value of all pixels on image and gray threshold are compared, and when gray-scale value is more than or equal to gray threshold, this pixel grey scale becomes " 255 ", otherwise gray scale becomes " 0 ", process formula as follows:

$g(x,y)=\left\{\begin{array}{cc}255& f(x,y)\&GreaterEqual;S\\ 0& f(x,y)<S\end{array}\right.$

Image before f (x, y) means to process, the bianry image after g (x, y) means to process, S means the gray threshold of setting, and wherein the selection of gray threshold S adopts process of iteration to obtain, and implementation step is as follows:

(1) obtain maximum gray scale and the minimum gradation value of image, be designated as respectively ZMax and ZMin, making initial threshold is S _K=(Zmax+Zmin)/2;

(2) according to threshold value S _KImage is divided into to the 1st family and the 2nd family, obtains respectively both average gray value Z1 and Z2.

(3) obtain new threshold value S _K+1=(Z1+Z2)/2.

(4) if specify a minimal value ε, have | S _K+1-S _K|<ε, if the value of approaching meets the demands substantially, gained is threshold value, S _K+1Be last iteration result, otherwise make S _K=S _K+1, re-execute top computation process, until meet the error requirements condition, wherein minimal value ε is taken as 10.

Step 3): to step 2) binary image obtained is removed noise processed, adopts median filter to carry out 4 filtering to image and removes noise.

Step 4): after step 3) is removed noise, in order accurately to obtain the length of crackle, first will carry out key extraction process, crackle is carried out to the key image that 5 corrosion treatments have obtained crackle afterwards.

Step 5): after the crackle backboneization, crackle is carried out to the length statistics, employing is from an end of crackle, traveling through successively the backbone of whole crackle, thereby obtain the length of crackle, is wherein that distance between pixel has two kinds of situations in length statistics, it between pixel, is the upper and lower, left and right four direction of mode arranged side by side, distance between this pixel arranged side by side is 1 pixel, and vergence direction has upper left, lower-left, upper right, bottom right four direction, and the distance between vergence direction is like this Individual pixel will be calculated respectively distance according to the connected mode between pixel when measuring, and the length of the crackle of measurement is 25.32.

Evidence: crackle physical length value is 24.83, and measuring length is 25.32, and its relative error is calculated as: $\mathrm{\&delta;}=\frac{|25.32-24.83|}{24.83}\&times;100\%=1.97\%,$ Error is controlled in 5%.

Claims (7)

1. a ceramic radome crackle automatic testing method, is characterized in that adopting the transmission image disposal route to detect, and concrete steps are: 1) the antenna house transmission image obtains; 2) gradation of image contrast enhancement processing, outstanding slit region; 3) binary conversion treatment; 4) medium filtering is removed noise processed; 5) the key extraction process of crackle; 6) each Crack length of statistical treatment, obtain the length value of each Crack.

2. ceramic radome crackle automatic testing method as claimed in claim 1, it is characterized in that: in step 1), in ceramic radome inside, light source is set, automatically carry out image acquisition at the outside ccd video camera that adopts of ceramic radome, obtain the gray scale transmission image of the whole different parts of ceramic radome.

3. ceramic radome crackle automatic testing method as claimed in claim 1, it is characterized in that: step 2) in, the gray-scale value of each pixel in the pointwise modification image, thus gradation of image dynamic range and contrast changed, if image is f (x, y), the image after processing is g (x, y), contrast increases and can be expressed as g (x, y)=T[f (x, y)], wherein T means the variation of input picture and output image corresponding pixel points grey scale mapping.

4. ceramic radome crackle automatic testing method as claimed in claim 1, it is characterized in that: in step 3), gray threshold S of image setting that gray scale is strengthened, gray threshold S adopts the iteration threshold method to try to achieve, then allow gray-scale value and the gray threshold S of each pixel on image compare, image is converted into the bianry image that only contains two gray levels the most at last:

$g(x,y)=\left\{\begin{array}{cc}255& f(x,y)\&GreaterEqual;S\\ 0& f(x,y)<S\end{array}\right.$

Wherein f (x, y) is original image, and g (x, y) is bianry image, and gray level " 255 " is non-defect area, and gray level " 0 " is the crack defect district.

5. ceramic radome crackle automatic testing method as claimed in claim 1, is characterized in that: in step 4), for given n number { a ₁, a ₂..., a _n, by their ordered arrangement by size, when n is odd number, the number that is positioned at centre position is called the intermediate value of this n number, and when n is even number, the mean value that is positioned at centre position two numbers is called the intermediate value of this n number, is designated as med[a ₁, a ₂..., a _n], to set the pixel neighborhood of a point in medium filtering, to this neighborhood, be all rank-ordered pixels in moving window, the gray-scale value by its gray scale intermediate value as processed pixel, array [x (i, j)] _{M * N}Through window, be A _nMedium filtering after, the output of pixel (i, j) is designated as:

In formula, A _n(i, j) means the neighborhood of point (i, j), and it contains n pixel.

6. ceramic radome crackle automatic testing method as claimed in claim 1, it is characterized in that: in step 5), the key extraction of crackle is to carry out corrosion treatment on the Width of crackle, until crack width only has a pixel unit, it has kept the topological property of crackle, and the process that the set A skeleton is turned to S (A) can be expressed as: And

In formula, B is structural element,

Continuous k the corrosion of expression to A, k is the number of times that A is etched into the front last iteration of empty set.

7. ceramic radome crackle automatic testing method as claimed in claim 1, it is characterized in that: in step 6), for every Crack length statistics wherein, be that the crackle that the backbone has been changed is traveled through since an end, after traversal whole piece crackle, the length of crackle has just come out, wherein the statistics of length comprises two kinds of situations, it between pixel, is the upper and lower, left and right four direction of mode arranged side by side, distance between this pixel arranged side by side is 1 pixel, vergence direction has upper left, lower-left, upper right, bottom right four direction, and the distance between vergence direction is like this

Individual pixel will, according to the connected mode between pixel, be calculated respectively distance when measuring.