CN104154999A - Compressed sensing-based multispectral imaging calculation system - Google Patents

Abstract

The invention discloses a compressed sensing-based multispectral imaging calculation system, which comprises a telescope imaging module, a digital micro reflector DMD and control module, an optical converging lens, a filter wheel, a photomultiplier tube PMT, a data acquisition module, and a multispectral image reconstruction module. According to the system, space information of a target scene is modulated according to a preset mathematical form of a modulation template, and the multispectral image of the target scene can be obtained through inversion of a subsequent data calculation method. The system has the advantages that no scanning is needed, data needed for target image reconstruction are few, detection sensitivity is high, and the structure is simple.

Description

A kind of calculating multi-optical spectrum imaging system based on compressed sensing

Technical field

The present invention relates to calculate the restructing algorithm of light spectrum image-forming technology and multispectral image, the fields such as signal processing.Be particularly related to a kind of calculating multi-optical spectrum imaging system based on compressed sensing.

Background technology

Multispectral, high light spectrum image-forming technology (referring to document 1) be take the Spectral Theory of material and is basis, relating to the fields such as Optical System Design, imaging technique, photodetection, signal processing and information excavating, spectral information transmission theory, object spectrum characteristics research, is one of current important earth observation from space technological means.Because high light spectrum image-forming technology can be obtained two-dimensional space information and the spectral information of target scene simultaneously, therefore in fields such as the detection of the detection identification of food safety detection, ground object target, metallic pollution in soil, mineral species analysis, Prediction of Flood Disaster, criminal investigation, artwork diagnosis, Military Application, be all widely used.

The imaging of traditional hyperspectral imager mainly contains two kinds of optical mechaical scanning formula, pull-broom types by grating beam splitting mode.Optical mechaical scanning formula imaging spectrometer is worked in optical mechaical scanning mode, and scanning mirror is swept to the other end from one end of swath, thereby makes the light that the ground object target of diverse location sends enter optical system imaging.Pull-broom type imaging spectrometer, in solid self-scanning mode, is used planar array detector unit to scan two-dimentional ground object target, and its space dimension pixel number is identical with the sampling unit of the given swath in ground, and spectrum dimension pixel number conforms to given spectrum channel number.Optical mechaical scanning formula imaging spectrometer is owing to having the moving component of scanning, thereby easily causes the instability of system.While wearing rail space pixel difference in optical mechaical scanning process simultaneously, obtain and will cause collection of illustrative plates post-processing difficulty very big.In addition, survey short greatly restricted quarter resolution and spectral resolution of integral time.Pull-broom type imager is due to its optical system structure, and imaging viewing field is very little, and calibration is simultaneously very difficult, and optical system is complicated, has the situation of spectrum bending.And because two kinds of imaging modes are all to adopt grating beam splitting, the use of single slit will inevitably bring the contradiction between spatial resolution and spectral resolution.

The multi-optical spectrum imaging system high light spectrum image-forming of comparing, sacrificed spectral resolution, but system architecture is very simple, at some, does not need the occasion of high spectral resolution still to have a wide range of applications.Tradition multispectral imaging adopts face battle array or linear array detector mostly, utilizes optical filter to realize multispectral imaging.If adopt linear array or single-element detector, need to spatially scan the complete picture that just can obtain target scene.With regard to current semiconductor technology, the planar array detector of visible spectral coverage is very ripe.But the production domesticization detector of infrared spectral coverage, especially mid and far infrared spectral coverage also cannot large-scale integrated.And still there is the problems such as heterogeneity in the current planar array detector of state-of-the-art infrared spectral coverage in the world.

Calculating light spectrum image-forming technology (referring to document 2) is the emerging imaging technique proposing both at home and abroad in recent years, be compared to traditional spectrum imaging system, calculate light spectrum image-forming and use special spatial light modulator as coded aperture, scenery target to be encoded, according to mathematical form modulation, seizure scenery spatial information and the spectral information imaging of set coded aperture in advance.Finally based on compressive sensing theory (referring to document 3,4,5), then obtain final multispectral image via the inverting of follow-up data computing method.Can adopt single pixel detector to obtain data.Be applied in infrared or mid and far infrared spectral coverage and there is important Research Significance.

Based on above background, the present invention proposes a kind of calculating multi-optical spectrum imaging system and figure spectrum reconstruction method based on compressed sensing.

List of references:

[1] Wang Jianyu, Shu Rong, Liu Yinnian, Ma Yanhua. imaging spectral technology introduction. Beijing: Science Press, 2011.

[2]Gehm M E,John R,Brady J D,Willett M R,Schulz J T.2008Opt.Express17 14013.

[3]Donoho D L.Compressed sensing[J].IEEE Transactions on Information Theory，2006，52(4)：1289-1306.

[4]Candès E，Romberg J，Tao T.Robust uncertainty principles：exact signal reconstruction from highly incomplete frequency information[J].IEEE Transactions on Information Theory，2006，52(2)：489-509.

[5]Candès E.Compressive sampling[C].International Congress of Mathematics，2006：1433-1452.

Summary of the invention

The object of this invention is to provide a kind of calculating multi-optical spectrum imaging system based on compressed sensing.Aspect detector, adopt single-element detector, solving domestic mid and far infrared spectral coverage detector cannot large-scale integrated and the bottleneck problem such as the non-homogeneous difference of detector self.Aspect data acquisition, based on compressive sensing theory, adopting a small amount of data is the multispectral image that restructural obtains target, and just compressed data in the process of sampling are alleviated collection, transmission, the storage pressure of big data quantity in traditional multispectral imaging.

Method of the present invention is used digital micro-mirror DMD as coded aperture, scenery target to be encoded, according to mathematical form modulation, seizure scenery spatial information and the spectral information imaging of set modulation template in advance.Finally based on compressive sensing theory, then via the inverting of follow-up data computing method, obtain the multispectral image of final goal scene.

The solution thinking that the present invention proposes is as follows:

As shown in Figure 1, the system of this invention comprises: telescope image-forming module 1, digital micro-mirror DMD and control module 2, optics plus lens 3, optical filter wheel 4, single pixel photomultiplier PMT 5, data acquisition module 6, multispectral image reconstructed module 7.It is characterized in that: the telescope focal length that telescope image-forming module 1 adopts is 304.8mm, and bore is 101.6mm; Its technical indicator of DMD that digital micro-mirror DMD and control module 2 adopt is: 1024 * 768 pixels, and pixel size is 13.69 microns; The focal length that optics plus lens 3 adopts is 40mm; Optical filter wheel 4 need to combine different optical filters according to spectral coverage; Single pixel photomultiplier PMT 5 work spectral coverages are at 300nm-900nm, and Pixel size 8mm, exports maximum dark voltage 20mv; The collection khaki quantization digit that data acquisition module 6 adopts is 16, sampling rate 250kS/s.

Workflow between each module of system is as follows:

Target scene images on digital micro-mirror DMD by telescope image-forming module 1.The spatial information of target setting scene is divided into m * n pixel, and spectral information is divided into L spectral coverage, and its figure spectrum information is expressed as φ (x, y, λ successively ₁), φ (x, y, λ ₂) ... φ (x, y, λ _l), the value of these functions equals the intensity level of the corresponding spectral coverage of specific pixel point in target scene;

Digital micro-mirror DMD and control module 2 be each loads a modulation template, thereby reaches the object of modulating target scene by the rollover states that modulation template changes upper each the little micro mirror of DMD;

DMD modulates for the first time, and making modulation template is θ ₁(m, n), concrete value is a m * n rank stochastic matrix setting in advance, and the value of matrix element is 0 or 1, and all elements are obeyed gaussian random and are distributed.Keep modulation template constant, the scene after modulation converges through optics plus lens 3, controls optical filter wheel 4, makes it allow the spectral coverage passing through to be followed successively by λ ₁, λ ₂... λ _l.After light signal coverlet pixel photomultiplier PMT 5 detections for each spectral coverage, through data acquisition module 6, gather, the voltage signal obtaining is used f successively ₁(x, y, λ ₁), f ₁(x, y, λ ₂) ... f ₁(x, y, λ _l) represent;

The like, the k time modulation of DMD, note modulation template is θ _k(m, n), with the process of modulating for the first time, gathers through data acquisition module 6, and the voltage signal obtaining is followed successively by:

f _k(x,y,λ ₁),f _k(x,y,λ ₂)...f _k(x,y,λ _L)；

Based on compressive sensing theory, method of the present invention proposes: the number of modulation template is k, the line number of observing matrix namely simultaneously, and value determines by the degree of rarefication of the needed spatial resolution of target scene reconstruction and target scene, and k is far smaller than N, and span is n is total amount of pixels of target scene, i.e. N=m * n; Because k is far smaller than N, therefore for each spectral coverage, the image of N pixel resolution of a small amount of k the signal value duplicate removal structure target scene that is equivalent to collect with data acquisition module 6.The meaning between the lines that is to say involuntaryly in the process gathering at data acquisition module 6 has compressed N-k data, thereby has alleviated collection, transmission, the storage pressure of big data quantity in traditional multispectral imaging;

Therefore, the signal that 7 pairs of data acquisition modules 6 of the multispectral image reconstructed module of system of the present invention collect is processed, and finally obtains the multispectral image of target scene; Treatment step is as follows:

1) Image Reconstruction to first spectral coverage of target scene, the signal that data acquisition module 6 is collected arranges following (1) formula of being write as:

$\left\{\begin{array}{c}{f}_1(x,y,{\mathrm{\λ}}_1)={\mathrm{\θ}}_1(m,n)\·\mathrm{\φ}(x,y,{\mathrm{\λ}}_1)+e_{11}\\ f_2(x,y{,\mathrm{\λ}}_1)={\mathrm{\θ}}_2(m,n)\·\mathrm{\φ}(x,y{,\mathrm{\λ}}_1)+e_{21}\\ .\\ .\\ .\\ f_k(x,y,{\mathrm{\λ}}_1)={\mathrm{\θ}}_k(m,n)\·\mathrm{\φ}(x,y,{\mathrm{\λ}}_1)+e_{k1}\end{array}\right.---\left(1\right)$

In above formula, e ₁₁, e ₂₁... e _k1noise for single pixel photomultiplier PMT 5;

(1) formula is expressed as to (2) formula with matrix equation:

F＝Θ·Φ+E (2)

In above formula, F is by signal f ₁(x, y, λ ₁), f ₂(x, y, λ ₁) ... f _k(x, y, λ ₁) k * 1 matrix that forms; Θ is k * N matrix, and line number k is modulation number of times, and columns N=m * n is modulation template θ _kthe several numbers of unit of (m, n), every a line of Θ is by corresponding θ _k(m, n) rearranges and forms; Φ is by φ (x, y, λ ₁) what form is N * 1 matrix; E is k * 1 noise matrix.Obviously, (2) formula is actually an ill-condition equation.Direct solution clearly has infinite a plurality of solution.But compressive sensing theory points out as long as Φ is sparse, or under the expression of certain orthogonal transformation, to have sparse property, and (2) formula that solves so will have special optimization method.The meaning of sparse property refers to and wherein comprises a large amount of data that go to zero, only has a small amount of nonzero value;

For natural scene, generally, can under the expression of some orthogonal transformations, there is sparse property.For example: Fourier transform, discrete cosine transform etc.For Φ, under discrete cosine transform, by its rarefaction representation, be following (3) formula:

For Φ, under discrete cosine transform, by its rarefaction representation, be following (3) formula:

Φ＝Ψ·α (3)

In above formula, the rarefaction representation that α is Φ, it is N * 1 matrix, degree of rarefication is: S, that is to say and in α, only contain S non-zero value; Ψ is N * N rank discrete cosine transform matrix;

So, (2) formula can be expressed as again shown in (4) formula:

F＝Θ·Φ+E＝Θ·Ψ·α+E＝T·α+E (4)

In above formula, T is k * N matrix, is referred to as sensing matrix in compressive sensing theory.(4), in formula, only having α is unknown number;

The method of Image Reconstruction solves the sparse factor alpha in (4) formula exactly.Clearly (4) formula is actually an ill-condition equation.Direct solution has infinite a plurality of solution, is therefore translated into the optimization problem as shown in the formula (5):

$\widehat{\mathrm{\α}}=\arg \min {\left|\right|\mathrm{\α}\left|\right|}_{L_1},\mathrm{st}.F=T\·\mathrm{\α}---\left(5\right)$

In above formula, L ₁represent 1 norm, for best fit approximation solution;

(5) the Optimization Solution algorithm steps of formula is as follows:

The first step: empty matrix I=[of initialization], residual matrix R=F;

Bis-Walk: each row in residual error R and T are done respectively to inner product, and find those row of inner product maximum, these row are taken out and add in matrix I;

Tri-Walk: upgrade residual error, R=F-I (I ^ti) ^-1i ^tf, wherein I ^ttransposed matrix (I for I ^ti) ^-1for (I ^ti) inverse matrix;

The 4th step: continuous sequential loop bis-Walk and the 3rd step, if residual error R meets: exit circulation, then forward the 5th step to.Wherein for all elements in matrix R, do a square then summation, r represents predefined error threshold, generally gets r<0.5;

The 5th step: the solution that final (5) formula is tried to achieve is following (6) formula:

$\widehat{\mathrm{\&alpha;}}={(I^T\&CenterDot;I)}^{-1}\&CenterDot;I^T\&CenterDot;F---\left(6\right)$

The image information of first spectral coverage of finally trying to achieve is expressed as (7) formula as follows:

$\mathrm{\&Phi;}=\mathrm{\&Psi;}\&CenterDot;\widehat{\mathrm{\&alpha;}}---\left(7\right)$

Rank, N * 1 matrix Φ in (7) formula is rearranged into the two-dimensional image that m * n rank matrix can obtain this spectral coverage target scene;

2), for the Image Reconstruction of second spectral coverage, the signal that data acquisition module 6 is collected rearranges, namely by step 1) in (1) formula write as (8) formula as follows:

$\left\{\begin{array}{c}{f}_1(x,y,{\mathrm{\&lambda;}}_2)={\mathrm{\&theta;}}_1(m,n)\&CenterDot;\mathrm{\&phi;}(x,y,{\mathrm{\&lambda;}}_2)+e_{12}\\ f_2(x,y,{\mathrm{\&lambda;}}_2)={\mathrm{\&theta;}}_2(m,n)\&CenterDot;\mathrm{\&phi;}(x,y{,\mathrm{\&lambda;}}_2)+e_{22}\\ .\\ .\\ .\\ f_k(x,y,{\mathrm{\&lambda;}}_2)={\mathrm{\&theta;}}_k(m,n)\&CenterDot;\mathrm{\&phi;}(x,y,{\mathrm{\&lambda;}}_2)+e_{k2}\end{array}\right.---\left(8\right)$

In above formula, e ₁₂, e ₂₂... e _k2noise for single pixel photomultiplier PMT (5);

In like manner, the like, for the Image Reconstruction of L spectral coverage, by step 1) in (1) formula write as (9) formula as follows:

$\left\{\begin{array}{c}{f}_1(x,y,{\mathrm{\&lambda;}}_L)={\mathrm{\&theta;}}_1(m,n)\&CenterDot;\mathrm{\&phi;}(x,y,{\mathrm{\&lambda;}}_L)+e_{1L}\\ f_2(x,y{,\mathrm{\&lambda;}}_L)={\mathrm{\&theta;}}_2(m,n)\&CenterDot;\mathrm{\&phi;}(x,y{,\mathrm{\&lambda;}}_L)+e_{2L}\\ .\\ .\\ .\\ f_k(x,y,{\mathrm{\&lambda;}}_L)={\mathrm{\&theta;}}_k(m,n)\&CenterDot;\mathrm{\&phi;}(x,y,{\mathrm{\&lambda;}}_L)+e_{\mathrm{kL}}\end{array}\right.---\left(9\right)$

In above formula, e _1L, e _2L... e _kLnoise for single pixel photomultiplier PMT (5);

So, to the 2nd Image Reconstruction to L spectral coverage, adopt with disposal route follow-up in step 1), finally can obtain the multispectral image of target scene.

The invention has the advantages that:

(1) system of the present invention adopts the figure spectrum information of DMD modulation target scene, adopts single pixel photomultiplier PMT to obtain data, and detection sensitivity is high, without any scanning, simple in structure.

(2) the present invention is based on compressive sensing theory, utilize a small amount of sampled data can restore complete multispectral image.From sampling, start just to have greatly reduced sampled data, greatly improved data acquisition, the transmission of system.Storage pressure.

Accompanying drawing explanation

Fig. 1 is a kind of calculating multi-optical spectrum imaging system and figure spectrum reconstruction method based on compressed sensing.Wherein: the 1st, telescope image-forming module; The 2nd, digital micro-mirror DMD and control module; The 3rd, optics plus lens; The 4th, optical filter wheel; The 5th, single pixel photomultiplier PMT; The 6th, data acquisition module; The 7th, multispectral image reconstructed module;

Fig. 2 is the schematic diagram of the concrete implementation system of the present invention.

Fig. 3 is the principle prototype based on Fig. 2, the multispectral image that utilizes spectrogram reconstructing method of the present invention to obtain.Wherein: A is target scene; The 1st, the image of 650nm spectral coverage after the reconstruct of target scenario A; The 2nd, the image of 540nm spectral coverage after reconstruct; The 3rd, the image of the 470nm spectral coverage obtaining after reconstruct; The 4th, use three three spectral coverage images that spectral coverage is synthetic above; The 5th, the panorama sketch of target scene.

Embodiment

Below in conjunction with Fig. 1, provide a better example of the present invention, be mainly described in further detail, but not be used for limiting scope of the present invention.

(1) first determine the basic fundamental parameter of each module of system components and parts used.Specific as follows: telescope image-forming module 1 adopts the telescope of Ai Mengte optics (Shenzhen) company limited, and selected focal length is 304.8mm, and bore is 101.6mm; The DMD that digital micro-mirror DMD and control module 2 adopt American TI Company to produce, technical indicator is 1024 * 768 pixels, and pixel size is 13.69 μ m, and control panel adopts the TI-Discovery-4100 coordinating with it; Optics plus lens 3 focal lengths are 40mm; Optical filter wheel 4 combines the optical filter of three spectral coverages as required, and spectral coverage is respectively 650nm, 540nm, 470nm; Single pixel photomultiplier PMT 5 adopts the H5784-01 product of Hamamatsu Photonics K.K company, and work spectral coverage is at 300nm-900nm, and Pixel size 8mm, exports maximum dark voltage 20mv; Data acquisition module 6 adopts the NI-USB-6211 capture card of America NI company, and technical indicator is: 16 of quantization digits, sampling rate 250kS/s.

As Fig. 2, the principle system based on Fig. 1 the system of utilizing above-mentioned given components and parts to build.

(2) telescope image-forming module 1 images in target scene on DMD.Digital micro-mirror DMD and a modulation template of control module 2 each loadings send to DMD, modulation template is that a size is 256 * 192, and obeys 0,1 matrix that gaussian random distributes, these modulation template are generated in advance, and this implements to generate 6000 templates.Yet selected DMD is 1024 * 768 pixels due to step (1), in order to allow DMD correctly identify, it is 1024 * 768 that actual loaded is chosen size to the template of DMD, exceeds 256 * 192 element and all uses " 0 " completion.By modulation, make the micro mirror of DMD in certain on off state, wherein " open " use " 1 " and represent, " passs " is with " 0 " expression (specifically make micro mirror overturn+12 ° (opening) and-12 ° (pass)).Deng micro mirror on off state stable after, can realize the modulation to target scene, the light of-12 ° of reflections of upset is dropped, the light of+12 ° of reflections of upset then enters follow-up optical system.

(3) modulation template of the every loading of DMD, is equivalent to modulation once.Every modulation+12 ° of upper micro mirror upsets in "On" state of DMD once time, make emission of light enter follow-up optical system by optical filter wheel 4, then combine the optical filter of different spectral coverage and realize the multispectral imaging to target scene.In the time of modulation each time, single pixel photomultiplier PMT 5 surveys the data of different spectral coverage, and the data of all spectral coverages of data acquisition module 6 synchronous acquisition.

(4) above-mentioned implementation step (1) (2) (3) repeats 6000 times, modulates 6000 times.Final data acquisition.Last multispectral image reconstructed module 7, by all data that collect, rearranges combination, and utilizes reconstructing method that the present invention proposes to obtain the multispectral image of target scene.For brief description, target scene is divided into 256 * 192 pixel sizes, and spectral coverage is divided into 650nm, 540nm, tri-spectral coverages of 470nm.To each spectral coverage reconstruct, need to solve 256 * 192 unknown numbers, and sampled data only has 6000, in the process that is equivalent to sample, compressed 256 * 192-6000=43152 data.

As Fig. 3, the principle prototype based on Fig. 2, utilizes the multispectral image of spectrogram reconstructing method gained of the present invention.

Claims (1)

1. the calculating multi-optical spectrum imaging system based on compressed sensing, it comprises: telescope image-forming module (1), digital micro-mirror DMD and control module (2), optics plus lens (3), optical filter wheel (4), single pixel photomultiplier PMT (5), data acquisition module (6), multispectral image reconstructed module (7); It is characterized in that:

It is 304.8mm that described telescope image-forming module (1) adopts focal length, the telescope that bore is 101.6mm;

Digital micro-mirror DMD in described digital micro-mirror DMD and control module (2) adopts 1024 * 768 pixels, and pixel size is the DMD of 13.69 μ m;

The capture card quantization digit that described data acquisition module (6) adopts is 16, sampling rate 250kS/s;

Annexation and the course of work between each module of system are as follows:

Target scene images on digital micro-mirror DMD by telescope image-forming module (1).The spatial information of target setting scene is divided into m * n pixel, and spectral information is divided into L spectral coverage, and its figure spectrum information is expressed as φ (x, y, λ successively ₁), φ (x, y, λ ₂) ... φ (x, y, λ _l), the value of these functions equals the intensity level of the corresponding spectral coverage of specific pixel point in target scene;

Digital micro-mirror DMD and control module (2) load a modulation template at every turn, and DMD modulates for the first time, and making modulation template is θ ₁(m, n), concrete value is a m * n rank stochastic matrix setting in advance, and the value of matrix element is 0 or 1, and all elements are obeyed gaussian random and are distributed.Keep modulation template constant, the scene after modulation converges through optics plus lens (3), controls optical filter wheel (4), makes it allow the spectral coverage passing through to be followed successively by λ ₁, λ ₂... λ _l; After light signal coverlet pixel photomultiplier PMT (5) detection for each spectral coverage, through data acquisition module (6), gather, the voltage signal obtaining is used f successively ₁(x, y, λ ₁), f ₁(x, y, λ ₂) ... f ₁(x, y, λ _l) represent;

The like, the k time modulation of DMD, note modulation template is θ _k(m, n), the span of k is: n=m * n wherein, S is Φ (x, y, λ _l) degree of rarefication; With the process of modulating for the first time, through data acquisition module (6), gather, the voltage signal obtaining is followed successively by:

f _k(x,y,λ ₁),f _k(x,y,λ ₂)...f _k(x,y,λ _L)；

Finally, the signal that multispectral image reconstructed module (7) collects data acquisition module (6) is processed, and finally obtains the multispectral image of target scene.