CN102629368A - Color image vignetting recovery method based on illumination surface modeling - Google Patents

Abstract

The invention belongs to the computer image processing field and relates to a color image vignetting recovery method based on illumination surface modeling. The method comprises the following steps: converting an original color vignetting image into an HSI space; extracting foreground and background regions of the vignetting image; using a color image decomposition technology to realize the decomposition of a structure and a texture of the original color vignetting image and acquire a color structure image, and converting the color structure image into the HSI space; in the background region of the image, selecting central points according to an uniformity principle; calculating a radial distance between any two central points; modeling all the points to be modeled and acquiring a curved surface after the modeling; taking the curved surface acquired through modeling as a vignetting function so as to acquire the color image after the vignetting recovery. The method of the invention has a good adaptability and is easy to be realized in a real project.

Description

A kind of coloured image vignetting restored method based on the illumination surface modeling

Technical field

The invention belongs to the Computer Image Processing field, relate to a kind of vignetting restored method of coloured image.

Background technology

Camera along with the increase of field angle, can will reduce through the skew ray area of beam area of photographic lens imaging when remote imaging gradually, and this can cause image bright in the middle of occurring, the phenomenon that the edge is dark, Here it is gradual halation phenomena.The existence of gradual halation phenomena can cause the image irradiation condition to change; Make the accuracy rate of target detection, image registration, image co-registration scheduling algorithm reduce greatly; Must eliminate; Vignetting restores the research content that has become fields such as remote sensing image processing, computer vision at present, has important Research Significance and actual application value.

Obtaining correct vignetting function is the key that realizes that the image vignetting restores.Traditional images vignetting restored method normally calculates the vignetting function based on relevant optics and geometric parameter, or confirms the vignetting function through related experiment in advance, lacks adaptivity, in actual engineering, is difficult to realize.Wherein, 1) traditional optical and geometric restitution method have tight theoretical foundation, can obtain vignetting function accurately, but precondition is to understand the correlation technique parameter of camera; And the relevant informations such as distance of camera and target when taking, this often is difficult to realization in actual engineering.2) need at first utilize standard video (like specific pattern on the blank sheet of paper) to experimentize based on the look-up table (LUT) and the fit method of lining by line scan,, utilize the table of comparisons again, through lining by line scan image carried out vignetting and restore to obtain the table of comparisons that influences coefficient of vignetting.This method need utilize standard video to obtain image vignetting function reference table in advance, and simultaneously each shooting all must be satisfied identical condition, this also to a great extent limit it in actual application in engineering.

Summary of the invention

In order to address the above problem; The present invention proposes a kind of coloured image vignetting restored method based on the illumination surface modeling; Its objective is to have no optics, geometric parameter information, also do not need to utilize in advance template to carry out under the condition of related experiment simultaneously, only according to the Illumination Distribution of colored vignetting image own; Utilize the method for three-dimensional modeling to obtain its vignetting function, thereby realize the automatic recovery of image gradual halation phenomena.

The coloured image vignetting restored method that the present invention proposes mainly comprises following step:

A kind of coloured image vignetting restored method based on the illumination surface modeling mainly comprises following step:

1) original color vignetting image f is transformed into the HSI space from rgb space, obtains the image f in H, S, three passages of I _H, f _S, f _IExtract the prospect and the background area of vignetting image;

2) utilize the coloured image decomposition technique, realize the decomposition of original color vignetting picture structure and texture, obtain its colored structural images f _uWith image f _uBe transformed into the HSI space, obtain I channel architecture image I _uAt I _uIn the background area of image, according to homogeneity principles of selected central point;

3) calculate any two central point p _i, p _jBetween radial distance

1≤i, j≤M, wherein || || represent Euclidean distance, M represents the central point sum;

4) calculate I channel architecture image I _uAt each central point p _iThe pixel value I at place _iAccording to formula

Calculating parameter c _i, 1≤i≤M; If certain treats that modeling point is for (x, y), the modeling point is treated in calculating, and (x is y) with each central point p _iBetween radial distance, d _i(x, y), 1≤i≤M is according to formula

Calculate the pixel value after this dot image modeling; Repeat above-mentioned steps, accomplish all are treated the modeling of modeling point, the curved surface I ' after the acquisition modeling;

5) I ' that obtains with modeling is as the vignetting function, utilizes itself and original image f _I, and normal illumination surface f _IRelation between the ' three: f _I'=f _I/ I ' recovers the original vignetting image of I passage f _INormal illumination surface f _I'; Utilize the illumination surface f after recovering _IThe original vignetting image of ' replacement I passage f _I, the original image f in H, the S Color Channel _H, f _SConstant, with image from the HIS space conversion to rgb space, the coloured image after obtaining vignetting and restoring.

The present invention is before carrying out modeling to the image illumination surface, and the method for at first utilizing coloured image to decompose extracts the structural information of original color image, realizes protecting the smothing filtering at edge, makes the image illumination surface satisfy the requirement of whole flatness; This measure can effectively reduce the conditional number of finding the solution matrix, improves the accuracy of image modeling.Through modeling is carried out on original color vignetting image illumination surface, the vignetting function of picture of can direct estimation publishing picture, and then realize the automatic recovery of image gradual halation phenomena; Because the present invention is without any need for optics, and the geometric parameter information during photograph taking, do not need to utilize template to carry out related experiment in advance yet, therefore have good adaptive property, in actual engineering, be easy to realize.

Description of drawings

Fig. 1 is the coloured image vignetting restored method theory diagram based on the illumination surface modeling.

Fig. 2 has provided coloured image modeling and vignetting recovery effect.Wherein, Fig. 2 (a) is an original color vignetting image; The structural images of Fig. 2 (b) for utilizing the coloured image decomposition technique to obtain; Fig. 2 (c) is a vignetting display foreground extracted region effect; The relevant central point of Fig. 2 (d) for choosing, wherein " o " represents the central point position; Fig. 2 (e) and Fig. 2 (f) are respectively the illumination surface three-dimensional distribution map before and after the colored vignetting structural images I component modeling; Fig. 2 (g) and Fig. 2 (h) are respectively the illumination surface energy profile before and after the colored vignetting structural images I component modeling; The vignetting recovery effect figure that Fig. 2 (i) utilizes the inventive method to obtain.

Embodiment:

As everyone knows, under identical illumination condition, the Illumination Distribution in the identical texture region should satisfy the characteristics of asymptotic variation; Yet real image is made up of different texture mostly, because the difference of reflection coefficient; Even under identical illumination condition; The illumination surface distributed of different texture also can distort, and therefore can not obtain the whole illumination patterns of image through modeling is carried out on entire image illumination surface.

It should be noted that; Nearly all natural image all is made up of prospect and background area; No matter how complicated foreground area is; But its background area is made up of single texture often, that is to say, the Illumination Distribution in most of image background regions can both satisfy the characteristics of asymptotic variation.Therefore, the present invention intends and in the background area with identical texture, chooses relevant central point, and utilizes above-mentioned central point that the integral image Illumination Distribution is carried out modeling, and then obtains the whole vignetting function of image, to realize the recovery of image gradual halation phenomena.At present existing several different methods can realize effective extraction in display foreground zone, repeats no more among the present invention.Be elaborated in the face of the present invention down.

1, coloured image decomposes

The purpose that coloured image decomposes is from original color image, to extract its structural images and texture image; The former mainly comprises the low-frequency information of image; Can realize protecting the smothing filtering at edge; The latter mainly comprises the high-frequency informations such as details of image, and promptly original image f can be decomposed into structure division u and texture part v, and the satisfied f=u+v that concerns.Coloured image decomposes can adopt several different methods; Like document [1] (referring to Luminita A.Vese; Stanley J.Osher. " Color texture modeling and color image decomposition in a variational-PDE approach; " Proceedings of the Eighth International Symposium on Symbolic and Numeric Algorithms for Scientific Computing (SYNASC ' 06); 2006, pp.103-110.) point out, from original image f, extract its structural images u; Can be regarded as a function minimization problem with fixed boundary, its energy functional minimum model can be expressed as:

$\underset{u,g1,g2}{\inf }\{\∫|\▿u|+\mathrm{\λ}\∫{|f-u-{\∂}_x{g}_1-{\∂}_x{g}_2|}^2\mathrm{dxdy}+\mathrm{\μ}[\∫{{\left(\sqrt{g_1^2+g_2^2}\right)}^p\mathrm{dxdy}]}^{\frac{1}{p}}\}---\left(1\right)$

Wherein, λ, μ, p are selected in advance correlation parameters, and the inf{} representative makes function { } reach minimum value,

Be conversion vector, u _x, u _yDistinguish the single order local derviation of representative structure image to the ranks coordinate,

The gradient of representative structure image.

With formula (1) respectively to u, g ₁, g ₂Ask local derviation, the Euler-Lagrange equation that can obtain being correlated with.Utilize alternative manner to find the solution, just can obtain structural images u.Repeat aforesaid operations at three color spaces of RGB, can realize the automatic decomposition of coloured image.

Document [2] (can be referring to Jean-Francois Aujol; Sung Ha Kang. " Color image decomposition and restoration. " Journal of Visual Communication and Image Representation; 2006; 17 (4), be to carry out picture breakdown pp:916-928.) according to the brightness and the colourity of image, be about to structural images u and be divided into colourity u _cWith brightness u _bTwo parts, and the satisfied u=u that concerns _c* u _bIn like manner, f=f is arranged _c* f _b, v=v _c* v _b, f=u+v, f wherein, v represents original image and texture image respectively; Can be according to minimum model

Find the solution structural images u, wherein

R, g, b is the RGB passage of representative image respectively,

The gradient of representative structure image; Utilize again to concern that v=f-u finds the solution texture image v, can realize the automatic decomposition of coloured image.

The method that present embodiment adopts document [1] to provide is carried out the automatic decomposition of colored vignetting image.In the present invention, the iteration initial value is made as u respectively ⁰=.f,

Wherein f is an original image, f _x, f _yDistinguish the single order local derviation of representative image to the ranks coordinate,

The gradient of representative image.Related parameter choosing is λ=0.01, μ=0.2, p=1; Inventor's research in earlier stage shows, chooses the smothing filtering that above-mentioned parameter can be realized image guarantor edge to a great extent, reduces noise and additional interference as far as possible, improves the modeling effect.

2, image illumination surface modeling

In recent years, be widely used in the three-dimensional modeling of smooth energy field such as light stream, energy distribution, electromagnetic field or smooth surface based on the method for RBF.The present invention is incorporated into image processing field with above-mentioned model, and has carried out corresponding improvement.Different with traditional light stream or energy field distribution, the illumination curved surface fluctuation of real image surface is violent, can't satisfy the requirement of whole flatness, can not utilize classic method directly image to be carried out modeling.In order to address the above problem; Before modeling is carried out on the image illumination surface; The method [1] that the present invention at first utilizes coloured image to decompose extracts the structural information of original color image, realizes protecting the smothing filtering at edge, makes the image illumination surface satisfy the requirement of whole flatness; This measure can effectively reduce the conditional number of finding the solution matrix, improves the accuracy of image modeling.

If N * N point chosen equably for modeling zone Ω in the integral image zone on Ω, remove the point in the foreground area, remaining point is designated as central point p _k, 1≤k≤M; The central point that utilization is chosen carries out modeling to imaging surface illumination, and concrete grammar can be referring to ([3] L.Ling and E.J.Kansa; " A least-squares preconditioner for radial basis functions collocation methods, " Advances in Computational Mathematics, vol.23; Pp.31-54,2005.) or ([4] Y.Duan, P.F.Tang; T.Z.Huang and S.J.Lai; " Coupling projection domain decomposition method and Kansa ' s method in elcectrostatic problems, " Computer physics Communications, vol.180; Pp.209-214,2009.) the present invention's method of adopting document [4] to provide is calculated the image function value at each point place after the modeling.With the gray level image is example, and concrete steps are following:

1) utilizes the picture breakdown technology, realize the automatic decomposition of original image structure and texture, obtain its structural images I _u, in its known region, according to homogeneity principles of selected central point;

2) calculate any two central point p _i, p _jBetween radial distance

1≤i, j≤M, wherein || || represent Euclidean distance, M represents the central point sum;

3) computation structure image I _uAt each central point p _iThe pixel value I at place _iAccording to formula

Calculating parameter c _i, 1≤i≤M;

4) calculate and to treat the modeling point (x is y) with each central point p _iBetween radial distance, d _i(x, y), 1≤i≤M is according to formula

Point after the computed image modeling (x, and the pixel value I ' that y) locates (x, y);

5) repeat above-mentioned steps, accomplish modeling, the curved surface I ' after the acquisition modeling being had a few.

3, vignetting restores

According to the vignetting model that Kang Weiss provides, vignetting image f ' (x y) can be expressed as: and f ' (x, y)=(x, y) (x, y), wherein (x y) represents original image to f to * I to f, and (x y) represents the vignetting function to I.Therefore, obtain vignetting function I (x, y) after, only need to utilize concern f (x, y)=f ' (x, y)/I (x y), can recover original image, thus the removal of realization gradual halation phenomena.

In the present invention, we only carry out modeling to the image I passage, utilize the illumination surface f after recovering _IThe original vignetting image of ' replacement I passage f _I, the original image f in H, the S Color Channel _H, f _SConstant; Utilize color of image space conversion formula again, with image from the HIS space conversion to rgb space, the coloured image after can obtaining vignetting and restoring.

From Fig. 2 (b), can find out; (a) compares with original graph 2; After the coloured image resolution process, image keep having realized under the condition at original edge level and smooth significantly, when having guaranteed image modeling to the flatness requirement of surperficial illumination; Effectively remove additional noise and interference, improved the modeling effect.

From Fig. 2 (f) and Fig. 2 (h), can find out, utilize the background area that image is carried out modeling after, the integral image illumination patterns demonstrates the trend of asymptotic variation, and consistent with traditional vignetting illumination patterns model, high in the middle of promptly, the edge is low; Therefore can be used for reflecting the illumination patterns of integral image.Can find out that from Fig. 2 (i) utilize method of the present invention, the gradual halation phenomena of image has obtained effective inhibition, has obtained gratifying result.

Claims (1)

1. coloured image vignetting restored method based on the illumination surface modeling mainly comprises following step:

1) original color vignetting image f is transformed into the HSI space from rgb space, obtains the image f in H, S, three passages of I _H, f _S, f _IExtract the prospect and the background area of vignetting image;

2) utilize the coloured image decomposition technique, realize the decomposition of original color vignetting picture structure and texture, obtain its colored structural images f _uWith image f _uBe transformed into the HSI space, obtain I channel architecture image I _uAt I _uIn the background area of image, according to homogeneity principles of selected central point;

3) calculate any two central point p _i, p _jBetween radial distance 1≤i, j≤M, wherein || || represent Euclidean distance, M represents the central point sum;

4) calculate I channel architecture image I _uAt each central point p _iThe pixel value I at place _iAccording to formula Calculating parameter c _i, 1≤i≤M; If certain treats that modeling point is for (x, y), the modeling point is treated in calculating, and (x is y) with each central point p _iBetween radial distance, d _i(x, y), 1≤i≤M is according to formula

Calculate the pixel value after this dot image modeling; Repeat above-mentioned steps, accomplish all are treated the modeling of modeling point, the curved surface I ' after the acquisition modeling;

5) I ' that obtains with modeling is as the vignetting function, utilizes itself and original image f _I, and normal illumination surface f _IRelation between the ' three: f _I'=f _I/ I ' recovers the original vignetting image of I passage f _INormal illumination surface f _I'; Utilize the illumination surface f after recovering _IThe original vignetting image of ' replacement I passage f _I, the original image f in H, the S Color Channel _H, f _SConstant, with image from the HIS space conversion to rgb space, the coloured image after obtaining vignetting and restoring.

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