CN1920881A - Image noise reducing method for Contourlet transform - Google Patents

Abstract

The invention relates to an image noise reduction method of Contourlet transformation region, wherein it comprises: translating the input image with noise; using Contourlet transformation to decompose said image at multiple sizes and directions, and in the Contourlet transformation region, using minimum Bayesian risk function to evaluate the Contourlet region factor; then processing Contourlet inverse transformation and inversed translating to obtain the noise reduced image; then repeating aforementioned steps, linearly averaging the noise reduced image, to obtain last noise reduced image. The invention can improve the quality of noise reduced image, to provide full and accurate target and background information, to be used in optical imaging, target detecting and safety detecting systems.

Description

A kind of image denoising method of Contourlet transform domain

Technical field

The present invention relates to the image denoising method of a kind of Contourlet (profile small echo) transform domain, this method adopts non-linear Bayesian (Bayes) the threshold value estimation technique to carry out noise reduction in the Contourlet transform domain, improves picture quality.In systems such as military field and non-military field such as optical imagery, target detection, security monitoring, all be widely used.

Background technology

Usually, image its obtain or transmission course in all can be subjected in various degree noise pollution, for follow-up further processing, the necessary noise reduction process of carrying out.The purpose of noise reduction is exactly to leach noise as much as possible, keeps all characteristic informations of image simultaneously to greatest extent, to improve the recovery quality of image.At present, image denoising method mainly is divided into linear filtering and nonlinear filtering two big classes.Traditional most of filtering method belongs to the former, as Wiener (Wei Na) filtering etc.And in non-linear filtering method, the most representative with collapse threshold noise-reduction method based on wavelet transformation.Because signal is through behind the wavelet transformation, signal mainly concentrates on the bigger wavelet coefficient of minority absolute amplitude, and noise then is dispersed on the less wavelet coefficient of some absolute amplitude, therefore, can utilize collapse threshold that wavelet coefficient is carried out noise reduction, reach the purpose of noise reduction.

Having benefited from wavelet transformation based on the collapse threshold noise-reduction method of wavelet transformation concentrates on main, important information in the image on the wavelet coefficient of minority.But, the two-dimentional separable wavelets conversion that is formed by tensor product by the one dimension small echo can only represent effectively that the unusual information of one dimension promptly puts unusual information, and two dimension or the unusual information of higher-dimension in the image can not be described effectively, as important informations such as line, profiles, thereby restricted the performance of wavelet de-noising method.The Contourlet conversion is as a kind of new signal analysis instrument, solved wavelet transformation and can not effectively represent the two dimension or the shortcoming of higher-dimension singularity more, can exactly the edge in the image be captured in the subband of different scale, different frequency, different directions.It not only has the multiple dimensioned characteristic of wavelet transformation, also has directivity and anisotropy that wavelet transformation does not have, therefore can be advantageously applied in the Flame Image Process that comprises image noise reduction.But these methods just select for use generic threshold value to come intercept signal simply, carry out noise reduction, and do not consider the characteristic distributions of Contourlet domain coefficient, and therefore, these algorithms are not optimum.

Summary of the invention

The objective of the invention is to deficiency at the existence of conventional images noise-reduction method, a kind of image denoising method of Contourlet transform domain has been proposed, this method adopts the non-linear Bayesian threshold value estimation technique to carry out noise reduction in the Contourlet transform domain, improves picture quality.

In order to achieve the above object, the present invention adopts following technical proposals:

A kind of image denoising method of Contourlet transform domain.It is characterized in that at first noisy image to input circulates after the translation, utilize the noisy image of Contourlet transfer pair input to carry out multiple dimensioned, multidirectional Sparse Decomposition, and estimate the Contourlet domain coefficient at the minimum Bayesian risk function of Contourlet transform domain utilization; The contrary circulation translation that next carries out Contourlet inverse transformation and corresponding translational movement obtains the noise reduction image after this translation; Repeat the step of front then, and the noise reduction image that at every turn obtains is carried out linear averaging, obtain final noise reduction image, reach the purpose of image noise reduction.

The concrete steps of above-mentioned noise-reduction method are as follows:

1. initialization setting.Make i=0, j=0 sets the maximal translation amount N on line direction and the column direction ₁And N ₂The middle LP that sets the Contourlet conversion simultaneously decomposes the direction Number of Decomposition L in number of plies K and every layer _k

2. the noisy image I of input is expert at and column direction on the translation that circulates, obtain the translation image

S _ij＝C _i，j(I)， (1)

Wherein i ∈ (0, N ₁) and j ∈ (0, N ₂) be respectively the translational movement on line direction and the column direction;

3. the translation image S to obtaining _IjCarry out multiple dimensioned, multidirectional Contourlet Sparse Decomposition, promptly

$[S_{\mathrm{lf}},S_{\mathrm{hf}}^{\left(\mathrm{1,1}\right)},\mathrm{\Λ},S_{\mathrm{hf}}^{(1,L_1)},S_{\mathrm{hf}}^{\left(\mathrm{2,1}\right)},\mathrm{\Λ},S_{\mathrm{hf}}^{(K,L_k)}]=T\left(S_{\mathrm{ij}}\right),---\left(2\right)$

Wherein T () is the Contourlet conversion.Thereby obtain a width of cloth low frequency subgraph as S _LfWith a series of high frequency subimage S with different resolution _Hf ^{(k, l)}, wherein k ∈ (1, K) and l ∈ (1, L _k) indicate that subimage is positioned at the l direction of k layer LP (the tower decomposition of Laplce);

4. to the high frequency subimage S after the Contourlet conversion _Hf ^{(k, l)}Carry out the threshold value noise reduction process, obtain the noise reduction subimage,

${S_D}_{\mathrm{hf}}^{(k,l)}=\mathrm{\Λ}(S_{\mathrm{hf}}^{(k,l)},T_B),---\left(3\right)$

Wherein, Λ () is a threshold function table, this paper select for use soft-threshold function Λ ()=sgn () max (, T _B), T _BBe threshold parameter.Choosing of threshold parameter is most important, because the Contourlet domain coefficient of image is obeyed generalized Gaussian distribution (GGD), satisfies the assumed conditions of Bayes method of estimation---and signal is obeyed generalized Gaussian distribution.Therefore, the threshold value method of estimation that this paper utilization is estimated based on Bayesian is estimated threshold parameter;

5. to all noise reduction high frequency subimage S that 4. obtain in the step _Dhf ^{(k, l)}With the low frequency subgraph that 3. obtains in the step as S _LfImplement the Contourlet inverse transformation, obtain the noise reduction image behind difference translation i and j on line direction and the column direction,

$S_{i,j}^{\mathrm{nf}}=T^{-1}(S_{\mathrm{lf}},{S_D}_{\mathrm{hf}}^{\left(\mathrm{1,1}\right)},\mathrm{\Λ},{S_D}_{\mathrm{hf}}^{(1,L_1)},{S_D}_{\mathrm{hf}}^{\left(\mathrm{2,1}\right)},\mathrm{\Λ},{S_D}_{\mathrm{hf}}^{(K,L_k)}),---\left(4\right)$

Wherein, T ^-1() is the Contourlet inverse transformation;

6. the image S that obtains in going on foot the 5th _{I, j} ^NfCarry out the reverse circulation translation of corresponding translational movement, have

$I_{i,j}^{\mathrm{nf}}=C_{-i,-j}\left(S_{i,j}^{\mathrm{nf}}\right).---\left(5\right)$

7. repeating step 2 to 6, up to i=N ₁And j=N ₂Till, stop repetition;

8. all S to obtaining _{I, j} ^Nf(i=0, Λ, N ₁J=0, Λ, N ₂) ask average, obtain the noise reduction image:

${\hat{g}}_{\mathrm{CT}}=\frac{1}{N_1{N}_2}\underset{i=0,j=0}{\overset{N_1,N_2}{\mathrm{\Σ}}}{I}_{i,j}^{\mathrm{nf}}.---\left(6\right)$

Above-mentioned adaptive threshold based on Bayesian Estimation, promptly $T_B={\mathrm{\σ}}_n^2/{\mathrm{\σ}}_x.$ Concrete estimating step is:

(a) for noise criteria difference σ _n, adopt the intermediate value of robustness to estimate,

${\widehat{\mathrm{\σ}}}_n=\frac{1}{0.6745L_K}\underset{i=1}{\overset{L_K}{\mathrm{\Σ}}}\mathrm{median}\left(\right|S_{\mathrm{hf}}^{(K,i)}\left|\right),---\left(7\right)$

S wherein _Hf ^{(K, i)}(i=1 Λ L _K) be the highest frequency coefficient;

(b) by ${\mathrm{\σ}}_y^2={\mathrm{\σ}}_x^2+{\mathrm{\σ}}_n^2,$ Have

${\widehat{\mathrm{\σ}}}_x=\sqrt{\max ({\widehat{\mathrm{\σ}}}_y^2-{\widehat{\mathrm{\σ}}}_n^2,0)},---\left(8\right)$

Wherein, ${\widehat{\mathrm{\σ}}}_y^2=\frac{1}{\mathrm{MN}}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{S}_{\mathrm{hf}}^{(k,i)}(m,n),$ S _Hf ^{(k, i)}It is the high frequency coefficient of being considered;

(c) therefore can get threshold parameter $T_B={\mathrm{\σ}}_n^2/{\mathrm{\σ}}_x.$

The inventive method has following conspicuous outstanding substantive distinguishing features and remarkable advantage compared with prior art:

The image denoising method of Contourlet transform domain provided by the invention is after at first the noisy image of importing being carried out a certain amount of circulation translation, utilize the noisy image of Contourlet transfer pair input to carry out multiple dimensioned, multidirectional Sparse Decomposition, and estimate the Contourlet domain coefficient at the minimum Bayesian risk function of Contourlet transform domain utilization, the contrary circulation translation that next carries out Contourlet inverse transformation and corresponding translational movement obtains the noise reduction image after this translation.Repeat the step of front then, and the noise reduction image that at every turn obtains is carried out linear averaging, obtain final noise reduction image, reach the purpose of image noise reduction.Concrete characteristics and advantage are:

(1) at two or higher-dimension singularity in the presentation video of the shortcoming of wavelet transformation in the most representative existing wavelet field threshold value noise-reduction method-effectively, the Contourlet conversion is applied in the image noise reduction, carry out multiple dimensioned, multi-direction decomposition, for follow-up noise reduction process provides sparse iamge description coefficient.

(2), the image denoising method of Contourlet transform domain has been proposed to the deficiency of conventional images noise reduction technology existence.

(3) because choosing of threshold parameter is most important to the method noise reduction.At this problem, Contourlet domain coefficient according to image is obeyed generalized Gaussian distribution (GGD), satisfying the assumed conditions of Bayes method of estimation---signal is obeyed generalized Gaussian distribution, and the threshold value method of estimation that the inventive method utilization is estimated based on Bayesian is estimated threshold parameter.

(4) the Contourlet territory threshold parameter that estimation obtains based on the Bayes method of estimation $T_B={\mathrm{\σ}}_n^2/{\mathrm{\σ}}_x$ Have adaptive characteristic, the variation of tracking signal effectively, thus can remove noise component effectively.

Image denoising method provided by the invention can improve the noise reduction image quality, target and background information more comprehensively and accurately is provided, reach comparatively ideal noise reduction.In systems such as military field and non-military field such as optical imagery, target detection, security monitoring, all have wide application prospects.

Description of drawings

Fig. 1 is the image denoising method block diagram of one embodiment of the invention.

Fig. 2 is Fig. 1 example noise reduction photo figure as a result.Among the figure, (a) be respectively input picture to (h) and be subjected to noise reduction result under the different noise pollution situations, noise intensity is respectively 15,20,25,30,35,40,45 and 50.(a) first width of cloth figure in (h) is the input that is subjected to noise pollution, and second width of cloth figure is the noise reduction image that adopts behind the inventive method noise reduction.

Embodiment

A preferred embodiment of the present invention is auspicious in conjunction with the accompanying drawings state as follows:

The image denoising method of this Contourlet transform domain, as shown in Figure 1.After at first the noisy image of importing being carried out a certain amount of circulation translation, utilize the noisy image of Contourlet transfer pair input to carry out multiple dimensioned, multidirectional Sparse Decomposition, and estimate the Contourlet domain coefficient at the minimum Bayesian risk function of Contourlet transform domain utilization, the contrary circulation translation that next carries out Contourlet inverse transformation and corresponding translational movement obtains the noise reduction image after this translation.Repeat the step of front then, and the noise reduction image that at every turn obtains is carried out linear averaging, obtain final noise reduction image, reach the purpose of image noise reduction.

Concrete steps are:

1. initialization setting.Make i=0, j=0 sets the maximal translation amount N on line direction and the column direction ₁And N ₂The middle LP that sets the Contourlet conversion simultaneously decomposes the direction Number of Decomposition L in number of plies K and every layer _k

2. the noisy image I of input is expert at and column direction on the translation that circulates, obtain the translation image

S _ij＝C _i，j(I)，

Wherein i ∈ (0, N ₁) and j ∈ (0, N ₂) be respectively the translational movement on line direction and the column direction;

3. the translation image S to obtaining _IjCarry out multiple dimensioned, multidirectional Contourlet Sparse Decomposition, promptly

$[S_{\mathrm{lf}},S_{\mathrm{hf}}^{\left(\mathrm{1,1}\right)},\mathrm{\Λ},S_{\mathrm{hf}}^{(1,L_1)},S_{\mathrm{hf}}^{\left(\mathrm{2,1}\right)},\mathrm{\Λ},S_{\mathrm{hf}}^{(K,L_k)}]=T\left(S_{\mathrm{ij}}\right),$

Wherein T () is the Contourlet conversion.Thereby obtain a width of cloth low frequency subgraph as S _LfWith a series of high frequency subimage S with different resolution _Hf ^{(k, l)}, wherein k ∈ (1, K) and l ∈ (1, L _k) indicate that subimage is positioned at the l direction of k layer LP (the tower decomposition of Laplce);

4. to the high frequency subimage S after the Contourlet conversion _Hf ^{(k, l)}Carry out the threshold value noise reduction process, obtain the noise reduction subimage,

${S_D}_{\mathrm{hf}}^{(k,l)}=\mathrm{\Λ}(S_{\mathrm{hf}}^{(k,l)},T_B),$

Wherein, Λ () is a threshold function table, this paper select for use soft-threshold function Λ ()=sgn () max (, T _B), T _BBe threshold parameter.Choosing of threshold parameter is most important, because the Contourlet domain coefficient of image is obeyed generalized Gaussian distribution (GGD), satisfies the assumed conditions of Bayes method of estimation---and signal is obeyed generalized Gaussian distribution.Therefore, the threshold value method of estimation that this paper utilization is estimated based on Bayesian is estimated threshold parameter.Based on the adaptive threshold of Bayesian Estimation, promptly $T_B={\mathrm{\σ}}_n^2/{\mathrm{\σ}}_x.$ Concrete estimating step is:

A. for noise criteria difference σ _n, adopt the intermediate value of robustness to estimate,

${\widehat{\mathrm{\σ}}}_n=\frac{1}{0.6745L_K}\underset{i=1}{\overset{L_K}{\mathrm{\Σ}}}\mathrm{median}\left(\right|S_{\mathrm{hf}}^{(K,i)}\left|\right),$

S wherein _Hf ^{(k, i)}(i=1 Λ L _K) be the highest frequency coefficient;

B. by ${\mathrm{\σ}}_y^2={\mathrm{\σ}}_x^2+{\mathrm{\σ}}_n^2,$ Have

${\widehat{\mathrm{\σ}}}_x=\sqrt{\max ({\widehat{\mathrm{\σ}}}_y^2-{\widehat{\mathrm{\σ}}}_n^2,0)},$

Wherein, ${\widehat{\mathrm{\σ}}}_y^2=\frac{1}{\mathrm{MN}}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{S}_{\mathrm{hf}}^{(k,i)}(m,n),$ S _Hf ^{(k, i)}It is the high frequency coefficient of being considered;

C. therefore can get threshold value $T_B={\mathrm{\σ}}_n^2/{\mathrm{\σ}}_x.$

5. to all noise reduction high frequency subimage S that 4. obtain in the step _Dhf ^{(k, l)}With the low frequency subgraph that 3. obtains in the step as S _LfImplement the Contourlet inverse transformation, obtain the noise reduction image behind difference translation i and j on line direction and the column direction,

$S_{i,j}^{\mathrm{nf}}=T^{-1}(S_{\mathrm{lf}},{S_D}_{\mathrm{hf}}^{\left(\mathrm{1,1}\right)},\mathrm{\Λ},{S_D}_{\mathrm{hf}}^{(1,L_1)},{S_D}_{\mathrm{hf}}^{\left(\mathrm{2,1}\right)},\mathrm{\Λ},{S_D}_{\mathrm{hf}}^{(K,L_k)}),$

Wherein, T ^-1() is the Contourlet inverse transformation;

6. to the image S that 5. obtains in the step _{I, j} ^NfCarry out the reverse circulation translation of corresponding translational movement, have

$I_{i,j}^{\mathrm{nf}}=C_{-i,-j}\left(S_{i,j}^{\mathrm{nf}}\right).$

7. repeating step is 2. to 6., up to i=N ₁And j=N ₂Till, stop repetition;

8. all S to obtaining _{I, j} ^Nf(i=0, Λ, N ₁J=0, Λ, N ₂) ask average, obtain the noise reduction image:

${\hat{g}}_{\mathrm{CT}}=\frac{1}{N_1{N}_2}\underset{i=0,j=0}{\overset{N_1,N_2}{\mathrm{\Σ}}}{I}_{i,j}^{\mathrm{nf}}.$

As can be seen from Figure 2, this image denoising method reduces the noise signal in the image better, has protected the material particular information in the image, has improved the quality of image.

Table 1 has provided noise-reduction method noise reduction result's of the present invention objective evaluation index.

Adopt Y-PSNR (PSNR) and least mean-square error (MSE) to weigh the quality of noise reduction image in the table, and then estimated the quality of noise-reduction method.

As can be seen from the table, no matter this image denoising method is aspect PSNR, still aspect MSE, all can obtain good noise reduction, reduces the noise signal in the image effectively, improves picture quality.

In a word, no matter be from the human eye vision effect, still from the objective evaluation index, show that all the inventive method reduces the noise signal in the image better, protected the material particular information in the image, improved the quality of image.

The noise reduction result of table 1 standard Barbara gray level image

σ n		15	20	25	30	35	40	45	50
										PSNR	Noisy image	24.69	22.20	20.34	18.81	17.59	16.50	15.60	14.79
The noise reduction image	27.10	26.24	25.40	24.53	23.67	23.27	22.80	22.37
									MSE		Noisy image	220.95	391.58	601.15	854.38	1133.12	1457.07	1793.62	2159.53
The noise reduction image	126.80	154.45	187.39	229.20	279.11	306.54	341.11	376.58

Claims (3)

1, a kind of image denoising method of Contourlet transform domain, it is characterized in that at first noisy image to input circulates after the translation, utilize the noisy image of Contourlet transfer pair input to carry out multiple dimensioned, multidirectional Sparse Decomposition, and estimate the Contourlet domain coefficient at the minimum Bayesian risk function of Contourlet transform domain utilization; Secondly, carry out the contrary circulation translation of Contourlet inverse transformation and corresponding translational movement, obtain the noise reduction image after this translation; Then, repeat the step of front, and the noise reduction image that at every turn obtains is carried out linear averaging, obtain final noise reduction image.

2, the image denoising method of Contourlet transform domain according to claim 1 is characterized in that:

1. initialization setting.Make i=0, j=0 sets the maximal translation amount N on line direction and the column direction ₁And N ₂The middle LP that sets the Contourlet conversion simultaneously decomposes the direction Number of Decomposition L in number of plies K and every layer _k

2. the noisy image I of input is expert at and column direction on the translation that circulates, obtain the translation image

S _ij＝C _i，j(I)，

Wherein i ∈ (0, N ₁) and j ∈ (0, N ₂) be respectively the translational movement on line direction and the column direction;

3. the translation image S to obtaining _IjCarry out multiple dimensioned, multidirectional Contourlet Sparse Decomposition, promptly

$[S_{\mathrm{lf}},S_{\mathrm{hf}}^{\left(\mathrm{1,1}\right)},\mathrm{\Λ},S_{\mathrm{hf}}^{(1,L_1)},S_{\mathrm{hf}}^{\left(\mathrm{2,1}\right)},\mathrm{\Λ},S_{\mathrm{hf}}^{(K,L_K)}]=T\left(S_{\mathrm{ij}}\right),$

Wherein T () is the Contourlet conversion.Thereby obtain a width of cloth low frequency subgraph as S _LfWith a series of high frequency subimage S with different resolution _Hf ^{(k, l)}, wherein k ∈ (1, K) and l ∈ (1, L _k) indicate that subimage is positioned at the l direction of k layer LP (the tower decomposition of Laplce);

4. to the high frequency subimage S after the Contourlet conversion _Hf ^{(k, l)}Carry out the threshold value noise reduction process, obtain the noise reduction subimage,

$S_{\mathrm{D\; hf}}^{(k,l)}=\mathrm{\Λ}(S_{\mathrm{hf}}^{(k,l)},T_B),$

Wherein, Λ () is a threshold function table, T _BBe threshold parameter, estimate threshold method estimation threshold parameter T with Bayesian _B

5. to all noise reduction high frequency subimage S that 4. obtain in the step _{D hf} ^{(k, l)}With the low frequency subgraph that 3. obtains in the step as S _LfImplement the Contourlet inverse transformation, obtain the noise reduction image behind difference translation i and j on line direction and the column direction,

$S_{i,j}^{\mathrm{nf}}=T^{-1}(S_{\mathrm{lf}},S_{\mathrm{D\; hf}}^{\left(\mathrm{1,1}\right)},\mathrm{\Λ},S_{\mathrm{D\; hf}}^{(1,L_1)},S_{\mathrm{D\; hf}}^{\left(\mathrm{2,1}\right)},\mathrm{\Λ},S_{\mathrm{D\; hf}}^{(K,L_K)}),$

Wherein, T ^-1() is the Contourlet inverse transformation;

6. to the image S that 5. obtains in the step _{I, j} ^NfCarry out the reverse circulation translation of corresponding translational movement, have

$I_{i,j}^{\mathrm{nf}}=C_{-i,-j}\left(S_{i,j}^{\mathrm{nf}}\right).$

7. repeating step is 2. to 6., up to i=N ₁And j=N ₂Till, stop repetition.

8. all S to obtaining _{I, j} ^Nf(i=0, Λ, N ₁J=0, Λ, N ₂) ask average, obtain the noise reduction image:

${\hat{g}}_{\mathrm{CT}}=\frac{1}{N_1{N}_2}\underset{i=0,j=0}{\overset{N_1,N_2}{\mathrm{\Σ}}}{I}_{i,j}^{\mathrm{nf}}.$

3, the image denoising method of Contourlet transform domain according to claim 1 is characterized in that described with Bayesian estimation threshold method estimation threshold parameter T _BStep be:

(a) for noise criteria difference σ _n, adopt the intermediate value of robustness to estimate,

${\widehat{\mathrm{\σ}}}_n=\frac{1}{0.6745L_K}\underset{i=1}{\overset{L_K}{\mathrm{\Σ}}}\mathrm{median}\left(\right|S_{\mathrm{hf}}^{(K,i)}\left|\right),$

S wherein _Hf ^{(K, i)}(i=1L L _k) be the highest frequency coefficient;

(b) by ${\mathrm{\σ}}_y^2={\mathrm{\σ}}_x^2+{\mathrm{\σ}}_n^2,$ Have

${\widehat{\mathrm{\σ}}}_x=\sqrt{\max ({\widehat{\mathrm{\σ}}}_y^2-{\widehat{\mathrm{\σ}}}_n^2,0)},$

Wherein, ${\widehat{\mathrm{\σ}}}_y^2=\frac{1}{\mathrm{MN}}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{S}_{\mathrm{hf}}^{(k,i)}(m,n),$ S _Hf ^{(k, i)}It is the high frequency coefficient of being considered;

(c) therefore can get threshold parameter $T_B={\mathrm{\σ}}_n^2/{\mathrm{\σ}}_x.$

Images