CN105321154A

CN105321154A - Image correction method capable of automatically detecting and removing grid lines

Info

Publication number: CN105321154A
Application number: CN201410337815.9A
Authority: CN
Inventors: 刘金虎; 方先成
Original assignee: Nanjing Perlove Radial Video Equipment Co Ltd
Current assignee: Nanjing Perlove Radial Video Equipment Co Ltd
Priority date: 2014-07-16
Filing date: 2014-07-16
Publication date: 2016-02-10

Abstract

The invention relates to an image correction method capable of automatically detecting and removing grid lines, and belongs to the technical field of medical instruments. The image correction method is characterized by comprising the steps of firstly carrying out detection on a region possibly containing grid lines in a Fourier image, and judging whether the region contains grid lines or not; determining horizontal starting and ending positions and vertical starting and ending positions of the grid line frequency if the region contains the grid lines; replacing values in a grid line frequency region with an average value of other high-frequency regions; and carrying out Fourier inverse transform, and returning an image with the grid lines being removed. The advantages are that whether a grid is utilized or not is not required to be specified in advance; no operation is carried out on the image under a grid-free condition, and image information is protected; an operation of grid line moving is carried out when the grid lines exist, and useful information of the image can be protected.

Description

A kind of automatic detection also removes the method for correcting image of grid line

Technical field

The invention belongs to technical field of medical instruments.

Background technology

X-ray production apparatus in use, always there is scattered ray in the ray that bulb is launched, at the thick position of shooting, such as during lumbar vertebrae, the existence of scattered ray can make picture quality significantly decline, so grid need be inserted when taking these positions, filter out the impact of scattered ray on film quality.

Grid plate outward appearance is the flat board of a thick 4-8mm, inner structure is that many eight-to-pica leads intersect arrangement and form, location is filled with easy radiotransparent material between two leads, and be bonded together, filling material can be wood, paper or aluminium flake etc., last up and down with thin aluminum sheet encapsulation, form grid plate, the parameter of grid has:

1, focal length: the vertical range of line to screen surface assembled by leads;

2, grid ratio: the ratio in leads height and leads gap;

3, grid density: the quantity of leads within the scope of unit distance.

For parallel gate, generally under equivalent material, grid density is less, and in unit distance, leads is fewer, and on image, grid line is more obvious; Grid density is larger, and on image, grid line is more not obvious; But the increase of grid density, grid price is more expensive, the cost of whole X-ray machine will increase, major part removed the method for grid line is in the past after known placement grid, zero-setting operation is carried out to fixed frequency region, but the method must limit and use grid method, otherwise very large to image contributions.

Summary of the invention

The object of the invention is to provide a kind of automatic detection and the method for correcting image removing grid line, and the image information loss removed after grid line is very little, and without the need to limiting the use of grid, facilitates medical diagnosis.

The technical solution adopted in the present invention is: it is characterized in that: first detect according to comprising grid line region in Fourier's image, judges whether to contain grid line; If there is grid line, determine the horizontal start-stop position of grid line frequency and vertical start-stop position;

Other high-frequency region mean value of value in grid line frequency field is replaced; Do Fourier inversion, return to image after grid.

Concrete bearing calibration is:

1, carry out Fourier transform to the band grid print image collected, obtain the distribution plan of image gradient, the brightness of gradient greatly then this point is strong, otherwise this brightness is weak, first we observe the energy distribution of image, if in spectrogram dark count more, so real image be smoother (because each point and neighborhood difference all little, gradient is relatively little), otherwise, if in spectrogram bright count many, so real image must be sharp-pointed, border is clearly demarcated and both sides, border pixel difference is larger, after frequency spectrum shift frequency to initial point, the frequency distribution of image take initial point as the center of circle, symmetrical, because image energy concentrates low frequency region, so spectrum energy integrated distribution is at initial point immediate vicinity, and be high-frequency information away from the part of initial point, grid line is similar to a series of border, belong to image high-frequency region, and brightness is very large, so in gradient map, can away from the gradient region significantly told in the high-frequency region of initial point corresponding to grid line.

2, set a threshold value, distinguish high-frequency region and low frequency region, according to above analysis, grid line only appears in high-frequency region, so in high-frequency region, marking this region of rectangular area T(comprising grid line frequency can be whole high-frequency region, but should get little as far as possible, optimal selection is the minimum rectangle that can comprise grid line frequency), and the brightness value in other high-frequency regions is asked an arithmetic mean, if being designated as M(T is whole high-frequency region, M is 0), simultaneously because the gradient map after Fourier transform is centrosymmetric, so only need consider high-frequency region on one side, the high-frequency region of another side only need do a centra-symmetric transformation.

3, in T, two-value is done by M, and filtering abnormity point, by this process after region be again labeled as T ~, then row statistical pixel values is pressed, by finding an obvious trough-crest-trough in row statistic curve, namely illustrating to there is grid line, orienting the position of two troughs, be designated as x1, x2 respectively, x1, x2 determine the level orientation of grid line frequency.

4, determined grid line and oriented x1, x2 (x2>x1), then in the statistical pixel values by row of T ~ inside, find an obvious trough-crest-trough, orient position y1, y2 of two troughs, y1, y2 determine the vertical orientations of grid line frequency.

5, when x1, x2, y1, y2 all determine, and value is all reasonably (such as x2>x1, y2>y1), so the value in this region is all set to M, and the region with this regional center symmetry is also all set to M.

6, Fourier inversion is done to amended gradient map, finally removed the correcting image after grid line.

Accompanying drawing explanation

Fig. 1: band 40 line grid original graph sectional drawing of the present invention;

Fig. 2: Fourier's image of the former figure of the present invention.

Fig. 3: the rectangular area T selected by the present invention.

Fig. 4: press row statistical pixel values curve in selected areas of the present invention.

Fig. 5: statistical pixel values curve by row in selected areas of the present invention.

Fig. 6: the present invention removes Fourier's image of grid line frequency.

Fig. 7: the present invention removes image sectional drawing after grid line.

Embodiment

1, gather a bright-field image (image taken during without the need to knowing whether and being and using grid), enter into grid line and detect removal module.

2, Fourier transform is done to image, obtain gradient map, determine in high-frequency region the rectangular area T that may comprise grid line information, pixels statistics is done by row after filtering in T, if by an obvious crest can be found in row statistic histogram, namely illustrate it is have grid line, continue following steps; If can not find, then illustrate that this figure is interior without grid line, directly jump out grid line and detect removal module, any operation is not done to collection figure.

3, after having determined grid line, first orient by the trough of two in row curve corresponding to crest, determine the horizontal reference position corresponding to grid line frequency field and final position, pixels statistics is done by row after filtering again in T, find out the position of two troughs, determine the vertical starting position corresponding to grid line frequency field and final position.

4, check that whether the value of four positions is reasonable, if rationally the value in grid line frequency field to be set to the mean value of other high-frequency region, and by gradient map with it centrosymmetric region be also set to the mean value of other high-frequency region, do Fourier inversion, obtain removing the image of grid lines and return.

Its advantage is: be the use of grid without the need to knowing whether in advance, can not go grid process in without grid situation, protection image information; Having in grid situation, removing grid line, improving picture quality.

Claims

1. automatically detect and remove the method for correcting image of grid line, it is characterized in that: first detect according to grid line region may be comprised in Fourier's image judge whether contain grid line; If there is grid line, determine the horizontal start-stop position of grid line frequency and vertical start-stop position; Other high-frequency region mean value of value in grid line frequency field is replaced; Do Fourier inversion, return to image after grid.