CN105278093A - Astronomical object imaging system - Google Patents

Abstract

The invention provides an astronomical object imaging system. According to the technical scheme of the invention, the system comprises a telescope objective lens, a wide-spectrum polarization splitting prism, a central control device, a digital miniature reflector type spatial light modulator, a first camera, a second camera, a first relay lens, a second relay lens, a third relay lens, a fourth relay lens, and a wide-spectrum quarter-wave plate. The first relay lens is located between the telescope objective lens and the wide-spectrum polarization splitting prism. The second relay lens is located between the wide-spectrum polarization splitting prism and the second camera. The third relay lens is located between the wide-spectrum polarization splitting prism and the digital miniature reflector type spatial light modulator. The fourth relay lens is located between the wide-spectrum polarization splitting prism and the first camera. The wide-spectrum quarter-wave plate is located between the wide-spectrum polarization splitting prism and the third relay lens. The first, second, third and fourth relay lens are respectively opposite to four usable surfaces of the wide-spectrum polarization splitting prism for placement. The system can achieve the clear imaging of a big-view-field astronomical object.

Description

A kind of system for astronomical target imaging

Technical field

The invention belongs to astronomical target imaging technical field, relate to a kind of astronomical target blur-free imaging method and system, relate to the method and system that a kind of out-of-focus image quality by evaluation point target realizes astronomical target blur-free imaging further.

Background technology

Method at present for astronomical target imaging mainly contains three kinds, is adaptive optics method, image deconvolution method and lucky formation method respectively.Adaptive optics method is with high costs and can only work within the scope of small field of view.Image deconvolution method is comparatively consuming time and also more limited to the improvement of image quality.The method of lucky imaging is by the long-time shooting to target, and from image sequence, filter out the excellent person of imaging superposed thus obtain the blur-free imaging of astronomical target, the method realizes simple, with low cost, is widely adopted.

For filtering out the excellent image of picture element, lucky formation method needs corresponding image quality evaluation means, common are Si Telieerbifa and shade of gray evaluation assessment, and Si Telieerbifa evaluates image quality by the encircled energy of point target in computed image.But the quality of picture quality is relevant to the intensity of atmospheric turbulence, this index of the encircled energy of point target accurately cannot describe the intensity of atmospheric turbulence, therefore for incorrect during assess image quality.Shade of gray evaluation assessment evaluates image quality by objective contour contrast in computed image, when the method is applied to the astronomical target of expansion, because comprise a lot of isoplanatic regions in image, the image quality independent variation of each isoplanatic region, the probability that view picture picture rich in detail can be caused to occur is very low, thus makes the image chosen there is the fuzzy serious problem of regional area.

The complicated mechanism of atmospheric turbulence, the light field that target can be made to send is subject to random disturbance.Traditional imaging means carries out superposition mutually by object intrusion light field and obtains imaging results, and this process does not utilize atmospheric disturbance information, cannot reconstruct real optical field distribution from image.Therefore when not utilizing guiding associated image, be directly difficult to judge whether its imaging is subject to atmospheric interference from target image, or the degree of interference is how many.

Summary of the invention

The technical matters that invention will solve is: the present invention is based on a kind of astronomical target imaging system newly, a kind of astronomical target imaging method is newly provided, the method realizes choosing of fortune image region by the uniformity coefficient of the out-of-focus image evaluating one or more independent point target, the splicing of different fortune image regions is obtained the blur-free imaging of the astronomical target of Large visual angle.

Technical scheme one of the present invention is:

A kind of astronomical target imaging system, comprise telescope objective (1), wide range polarization splitting prism (2), central control unit (3), digital micromirror part (DigitalMicroDevice, DMD) formula spatial light modulator (4), first camera (5), second camera (6), first relay lens (7), second relay lens (8), 3rd relay lens (9), 4th relay lens (10), wide spectrum quarter wave plate (11), it is characterized in that: the first relay lens (7) is positioned between telescope objective (1) and wide range polarization splitting prism (2), its position, focal plane

Overlap with telescope objective (1) position, focal plane; Second relay lens (8) is positioned between wide range polarization splitting prism (2) and second camera (6), and its position, focal plane overlaps with the light-sensitive surface position of second camera (6); 3rd relay lens (9) is positioned between wide range polarization splitting prism (2) and digital micromirror part formula spatial light modulator (4), and its position, focal plane overlaps with digital micromirror part formula spatial light modulator (4) light-sensitive surface position; 4th relay lens (10) is positioned between wide range polarization splitting prism (2) and first camera (5), stagger certain distance in the light-sensitive surface position of its position, focal plane and first camera (5), this distance is called defocusing amount, and focal plane is at the front of first camera (5) light-sensitive surface and rear.Wide spectrum quarter wave plate (11) is positioned between wide range polarization splitting prism (2) and the 3rd relay lens (9).First relay lens (7), the second relay lens (8), the 3rd relay lens (9), the 4th relay lens (10) are just put four of wide range polarization splitting prism (2) available surfaces respectively, the main shaft of four relay lenses all perpendicular to wide range polarization splitting prism (2) corresponding square surface and by the mid point of square surface.Central control unit (3) is electrically connected with first camera (5), second camera (6) and digital micromirror part formula spatial light modulator (4) respectively.

More directly perceived in order to state, hereafter first camera (5) is called out of focus camera (5), second camera (6) is called in burnt camera (6).

Technical scheme two of the present invention is:

A kind of astronomical target imaging method, the astronomical target imaging system utilizing technical scheme one to provide, specifically comprises the steps:

The first step, arranges imaging coordinate system:

The light-sensitive surface of digital micromirror part formula spatial light modulator (4) sets up UOV coordinate system, and wherein UOV coordinate origin O is positioned at the center of light-sensitive surface, and U axle and V axle are parallel to horizontal edge and the vertical edge of light-sensitive surface respectively.The light-sensitive surface of out of focus camera (5) sets up XO ₁y-coordinate system, wherein XO ₁y-coordinate system initial point O ₁be positioned at the center of light-sensitive surface, X-axis and Y-axis are parallel to horizontal edge and the vertical edge of light-sensitive surface respectively.The light-sensitive surface of burnt camera (6) sets up X ₁o ₂y ₁coordinate system, wherein X ₁o ₂y ₁coordinate origin O ₂be positioned at the center of light-sensitive surface, X ₁axle and Y ₁axle is parallel to horizontal edge and the vertical edge of light-sensitive surface respectively.

Second step, selects the independent point target being suitable for out of focus light field and evaluating.

Utilization is carried out continuous print image acquisition at burnt camera (6) and is obtained astronomical target image, if at least there are two point targets in the astronomical target image of certain width by three screenings below, then stops image acquisition:

First time screening: select the point target that brightness is enough strong.The enough strong point target of brightness refers to that in the correspondence image that this point target gathers at out of focus camera (5), pixel average gray value is greater than the threshold value of setting, and arrange threshold value according to actual conditions, usually arranging threshold value is 10.The point target number supposing to meet these screening conditions is e (e >=2).

Programmed screening: in e the point target filtered out, suppose that the distance wherein between some point targets and its point target of closing on most is d, if d meets formula one, then pass through programmed screening:

$d>24.4\frac{{\mathrm{\λ}}_{mean}\×F}{D}$ (formula one)

In formula one, F is the focal length of telescope objective (1), and D is telescope objective (1) bore, λ _meanfor the spectral radiance mean wavelength of observed object.

Suppose that point target number is f (1≤f≤e) after programmed screening.

Third time screening: in f the point target filtered out, the distance between certain point target and its point target of closing on most is d ₁if, d ₁meet formula two, then by third time screening:

$d_1>\frac{\left|Z\right|\×D}{F}$ (formula two)

Z in formula two is defocusing amount.

If be independent point target by remaining point target after above three screenings, number is M (1≤M≤f).

3rd step, controls spatial light modulator specific region and realizes reflected incident light.

The angle of inclination of the tiny mirror of adjustment digital micromirror part formula spatial light modulator (4), makes not comprise light corresponding to independent point order target area and deflects after the reflection of digital micromirror part formula spatial light modulator (4) and lose.Only has the direct plane reflection of light that pinpoint target point sends, reflected light have passed through wide range quarter wave plate due to twice, therefore polarization state there occurs 90 degree of deflections, this light produces 90 ° turning back in the direction of propagation when wide range polarization splitting prism (2) subsequently, finally enters out of focus camera (5) for imaging.

Through above-mentioned steps, the state of astronomical target imaging system has adjusted, and utilizes the astronomical target imaging system adjusted to carry out multiple image collection below and screening.

4th step, calculates the out-of-focus image evenness index that each independent point target is corresponding.

Make out of focus camera (5) and in burnt camera (6) synchronous working, suppose to acquire p width image respectively, the image sequence that out of focus camera (5) gathers is I _unfocus={ I ¹ _unfocus, I ² _unfocus... I ^p _unfocus, the image sequence gathered at burnt camera (6) is I _focus={ I ¹ _focus, I ² _focus... I ^p _focus.

For I _unfocusa wherein width out-of-focus image I in sequence ^k _unfocus(1≤k≤p), if i-th independent point target in this image on out of focus camera (5) light-sensitive surface, the coordinate of corresponding registration point is (x ⁱ, y ⁱ), independent point target corresponding to XO ₁pixel (a meeting formula four in Y-coordinate system _j, b _j) total N number of, the gray-scale value of pixel is K _j, 1≤j≤N:

${(a_j-x^i(1+\frac{Z}{F}\left)\right)}^2+{(b_j-y^i(1+\frac{Z}{F}\left)\right)}^2\≤\frac{\left|Z\right|\×D}{2F}$ (formula four)

Calculate independent point target corresponding uniformity degree of image index

$I_i^k=\underset{j=1}{\overset{N}{\Σ}}\left|K_j-\frac{\underset{j=1}{\overset{N}{\Σ}}{K}_j}{N}\right|$ (formula five)

5th step, filters out fortune image region.

For independent point target A _i(1≤i≤M), total P uniformity degree of image index suppose that the sequence number corresponding to the element that this sequence intermediate value is minimum is q (1≤q≤P).To I _focusin sequence, q frame is at burnt image, supposes the pixel (x in any one piece of image-region on burnt image ₁, y ₁if) meet formula six:

${(x_1-x_1^i)}^2+{(y_1-y_1^i)}^2\≤C$

$24.4\frac{{\mathrm{\&lambda;}}_{mean}\&times;F}{D}<C<\frac{min\left(\right(H/2-\left|x_1\right|),(W/2-\left|y_1\right|\left)\right)}{2}$ (formula six)

Then this image-region is independent point target A _ithe fortune image region that (1≤i≤M) is corresponding.In formula six, H and W is respectively physical height and the width of out of focus camera sensor, and C is that the artificial fortune image arranged selects radius.The image corresponding to other independent point target implements same operation, can obtain corresponding fortune image region equally.

6th step, implements splicing to all image-regions filtered out.

The initial pictures of the image same size setting up a width and obtain at burnt camera (6), in initial pictures, the gray-scale value of each pixel is zero, then divides the process of the following two kinds situation:

Situation one, if zero lap, the then correspondence position copying to initial pictures of above-mentioned fortune image region content between fortune image region corresponding to two different independent point targets.

Situation two, if exist overlapping between fortune image region corresponding to two different independent point targets, then uses the image split-joint method based on mutual information to be stitched together in two fortune image regions, and copies to the correspondence position of initial pictures.

The initial pictures obtained after above-mentioned process is imaging results.

The invention has the beneficial effects as follows: use a kind of brand-new independent point target light field evaluation method to replace traditional gradation of image evaluation assessment, obtain while multiple independent point target light fields simultaneously on combined with hardware, reach the object to astronomical Extended target multizone blur-free imaging.The present invention not only significantly improves the probability obtaining fortune image, and makes the target image sharpness of acquisition higher.

Accompanying drawing explanation

Fig. 1 is astronomical target imaging system principle schematic diagram provided by the invention;

Fig. 2 is concrete implementing procedure figure;

Fig. 3 is two point target out-of-focus images do not obtained in the same time in experiment;

Fig. 4 be two moment point targets that Fig. 3 is corresponding at burnt image.

Embodiment

Below with reference to Figure of description, the present invention is described in further details.

In Fig. 1, the coke ratio of the relay lens 7,8,9,10 that focal length is identical should be greater than the coke ratio of telescope objective 1.The optical band of wide range polarization splitting prism 2 can be selected according to infrared radiation characteristics (as visible light wave range or infrared band).The size of wide range polarization splitting prism 2 should meet all can be injected by the light of relay lens 1 outgoing, and relay lens 7,8,9,10 should be installed near wide range polarization splitting prism 2 as much as possible, to be lowered into the vignetting effect of picture.View data is sent at burnt camera 6 and out of focus camera 5 to central control unit 3 in figure.Central control unit 3 sends image acquisition control signal respectively by control signal alignment at burnt camera 6 and out of focus camera 5; Central control unit 3 is transmitted control signal by control signal alignment digital micromirror part formula spatial light modulator 4, controls the polarization state of spatial light modulator 4 specific region.The installation warrants of the defocusing amount of out of focus camera 5 light-sensitive surface is as follows: set atmospheric turbulence coherent length (i.e. Freid constant) as γ ₀, then defocusing amount Z should meet following formula:

$5\&times;\frac{F^2\&times;{\mathrm{\&lambda;}}_{mean}}{{\mathrm{\&gamma;}}_0^2}<\left|Z\right|<2\&times;\frac{F\&times;min(H,W)}{D}$ (formula seven)

In formula seven, Z can be positive number or negative, and positive number shows that camera is to the direction out of focus away from telescope objective 1, and negative shows that camera is to the direction out of focus near telescope objective 1.The telescope objective 1 that the present invention relates to refractor object lens for the best.The camera that the present invention relates to adopts industrial camera.The central control unit 3 that the present invention relates to adopts multi-purpose computer or special controller (realizing as adopted DSP or FPGA).

Some step of technical solution of the present invention two is explained in detail.

Second step, selects the independent point target being suitable for out of focus light field and evaluating.In this step, in the continuous working that burnt camera 6 is independent, gather multiple image, until just stop gathering image when there is the independent point target being suitable for the evaluation of out of focus light field in image.The independent point destination number selected looks atmospheric turbulence intensity and concrete astronomical target property determines.What in the second condition of this step, " target of closing on most " referred to can be point target also can be Extended target.

3rd step, controls spatial light modulator specific region and realizes reflected incident light.In the process implementing this step, be usually idle at burnt camera 6 and out of focus camera 5, they do not need to gather image.Once selected and achieve polarization state and be biased, then start working at burnt camera 6 and out of focus camera 5, carry out image acquisition in the specific region of digital micromirror part formula spatial light modulator 4.

7th step, implements splicing to all image-regions filtered out.The image split-joint method based on mutual information that this step adopts is known method and means, the idiographic flow of method and relevant introduction are in detail see document (Zhou Hu, Yang Jianguo, Li Beizhi. based on plane picture splicing and the measuring technique thereof of mutual information measure, Donghua University's journal natural science edition, the 6th phase in 2011).

In order to prove the feasibility of the inventive method, we have carried out emulation experiment.In emulation experiment, the bore of the telescope objective 1 of astronomical target imaging system is 80mm, focal length is 480mm, the diameter of the relay lens 7,8,9,10 used is 25.4mm, focal length is 50mm, out of focus camera 5 and have selected the black and white industrial camera of Thorlabs company at burnt camera 6, the two achieves the function of synchronous triggering work by signal wiring.Use the industrial computer of Tai Yanhua company production as central control unit 3 in emulation experiment.Conveniently and clearly prove experimental result, utilize system to adjust the distance the point target imaging of about 700m, the left figure of Fig. 3 and right figure is by the out-of-focus image of out of focus camera 5 two these point targets do not collected in the same time in emulation experiment.Contrast from figure and can find: when different when, because the degree of atmospheric turbulence is different, the out-of-focus image uniformity coefficient of point target is also different.Fig. 4 to obtain by Fig. 3 under the corresponding moment condition of image by the target collected at burnt camera 6 at burnt image, (left figure is to left figure, right figure is to right figure) visible in figure, when out-of-focus image uniformity coefficient is better, the corresponding image quality at burnt image is obviously better, the uniformity coefficient of above-mentioned description of test out-of-focus image reflects that image is subject to the degree of Turbulent Flow Effects, the image that in out-of-focus image, evenness index is the highest correspond to by Turbulent Flow Effects minimum at burnt image, thus explanation utilizes the uniformity coefficient index of out-of-focus image can judge the influence degree of atmospheric turbulence to imaging, and can according to this criterion filter out image quality best at burnt image.Therefore the method feasibility of this Foundation is experiment invention provides support.

Claims (2)

1. an astronomical target imaging system, comprise telescope objective (1), wide range polarization splitting prism (2), central control unit (3), digital micromirror part formula spatial light modulator (4), first camera (5), second camera (6), first relay lens (7), second relay lens (8), 3rd relay lens (9), 4th relay lens (10), wide spectrum quarter wave plate (11), it is characterized in that: the first relay lens (7) is positioned between telescope objective (1) and wide range polarization splitting prism (2), its position, focal plane overlaps with telescope objective (1) position, focal plane, second relay lens (8) is positioned between wide range polarization splitting prism (2) and second camera (6), and its position, focal plane overlaps with the light-sensitive surface position of second camera (6), 3rd relay lens (9) is positioned between wide range polarization splitting prism (2) and digital micromirror part formula spatial light modulator (4), and its position, focal plane overlaps with digital micromirror part formula spatial light modulator (4) light-sensitive surface position, 4th relay lens (10) is positioned between wide range polarization splitting prism (2) and first camera (5), stagger certain distance in the light-sensitive surface position of its position, focal plane and first camera (5), this distance is called defocusing amount, wide spectrum quarter wave plate (11) is positioned between wide range polarization splitting prism (2) and the 3rd relay lens (9), first relay lens (7), the second relay lens (8), the 3rd relay lens (9), the 4th relay lens (10) are just put four of wide range polarization splitting prism (2) available surfaces respectively, the main shaft of four relay lenses all perpendicular to wide range polarization splitting prism (2) corresponding square surface and by the mid point of square surface, central control unit (3) is electrically connected with first camera (5), second camera (6) and digital micromirror part formula spatial light modulator (4) respectively.

2. an astronomical target imaging method, the astronomical target imaging system utilizing claim 1 to provide, specifically comprises the steps:

The first step, arranges imaging coordinate system:

The light-sensitive surface of digital micromirror part formula spatial light modulator (4) sets up UOV coordinate system, and wherein UOV coordinate origin O is positioned at the center of light-sensitive surface, and U axle and V axle are parallel to horizontal edge and the vertical edge of light-sensitive surface respectively; The light-sensitive surface of out of focus camera (5) sets up XO ₁y-coordinate system, wherein XO ₁y-coordinate system initial point O ₁be positioned at the center of light-sensitive surface, X-axis and Y-axis are parallel to horizontal edge and the vertical edge of light-sensitive surface respectively; The light-sensitive surface of burnt camera (6) sets up X ₁o ₂y ₁coordinate system, wherein X ₁o ₂y ₁coordinate origin O ₂be positioned at the center of light-sensitive surface, X ₁axle and Y ₁axle is parallel to horizontal edge and the vertical edge of light-sensitive surface respectively;

Second step, select the independent point target being suitable for out of focus light field and evaluating:

Utilization is carried out continuous print image acquisition at burnt camera (6) and is obtained astronomical target image, if at least there are two point targets in the astronomical target image of certain width by three screenings below, then stops image acquisition:

First time screening: select the point target that brightness is enough strong; The enough strong point target of brightness refers to that in the correspondence image that this point target gathers at out of focus camera (5), pixel average gray value is greater than the threshold value of setting, arranges threshold value according to actual conditions; The point target number supposing to meet these screening conditions is e, e >=2;

Programmed screening: in e the point target filtered out, suppose that the distance wherein between some point targets and its point target of closing on most is d, if d meets formula one, then pass through programmed screening:

$d>24.4\frac{{\mathrm{\&lambda;}}_{mean}\&times;F}{D}$ (formula one)

In formula one, F is the focal length of telescope objective (1), and D is telescope objective (1) bore, λ _meanfor the spectral radiance mean wavelength of observed object;

Suppose that point target number is f, 1≤f≤e after programmed screening;

Third time screening: in f the point target filtered out, the distance between certain point target and its point target of closing on most is d ₁if, d ₁meet formula two, then by third time screening:

$d_1>\frac{\left|Z\right|\&times;D}{F}$ (formula two)

Z in formula two is defocusing amount;

If be independent point target by remaining point target after above three screenings, number is M, 1≤M≤f;

3rd step, controls spatial light modulator specific region and realizes reflected incident light:

The angle of inclination of the tiny mirror of adjustment digital micromirror part formula spatial light modulator (4), makes not comprise light corresponding to independent point order target area and deflects after the reflection of digital micromirror part formula spatial light modulator (4) and lose; Only has the direct plane reflection of light that pinpoint target point sends;

The astronomical target imaging system adjusted is utilized to carry out multiple image collection below and screening;

4th step, calculates the out-of-focus image evenness index that each independent point target is corresponding;

Make out of focus camera (5) and in burnt camera (6) synchronous working, suppose to acquire p width image respectively, the image sequence that out of focus camera (5) gathers is I _unfocus={ I ¹ _unfocus, I ² _unfocus... I ^p _unfocus, the image sequence gathered at burnt camera (6) is I _focus={ I ¹ _focus, I ² _focus... I ^p _focus;

For I _unfocusa wherein width out-of-focus image I in sequence ^k _unfocus, 1≤k≤p, if i-th independent point target in this image on out of focus camera (5) light-sensitive surface, the coordinate of corresponding registration point is (x ⁱ, y ⁱ), 1≤i≤M; Independent point target corresponding to XO ₁pixel (a meeting formula four in Y-coordinate system _j, b _j) total N number of, the gray-scale value of pixel is K _j, 1≤j≤N:

${(a_j-x^i(1+\frac{Z}{F}\left)\right)}^2+{(b_j-y^i(1+\frac{Z}{F}\left)\right)}^2\&le;\frac{\left|Z\right|\&times;D}{2F}$ (formula four)

Calculate independent point target corresponding uniformity degree of image index

$I_i^k=\underset{j=1}{\overset{N}{\&Sigma;}}|K_j-\frac{\underset{j=1}{\overset{N}{\&Sigma;}}{K}_j}{N}|$ (formula five)

5th step, filters out fortune image region;

For independent point target A _i, total P uniformity degree of image index ... suppose that the sequence number corresponding to the element that this sequence intermediate value is minimum is q, 1≤q≤P; To I _focusin sequence, q frame is at burnt image, supposes the pixel (x in any one piece of image-region on burnt image ₁, y ₁if) meet formula six:

${(x_1-x_1^i)}^2+{(y_1-y_1^i)}^2\&le;C$

$24.4\frac{{\mathrm{\&lambda;}}_{mean}\&times;F}{D}<C<\frac{min\left(\right(H/2-\left|x_1\right|),(W/2-|y_1\left|\right))}{2}$ (formula six)

Then this image-region is independent point target A _icorresponding fortune image region; In formula six, H and W is respectively physical height and the width of out of focus camera sensor, and C is that the artificial fortune image arranged selects radius; The image corresponding to other independent point target implements same operation, can obtain corresponding fortune image region equally;

6th step, implements splicing to all image-regions filtered out;

The initial pictures of the image same size setting up a width and obtain at burnt camera (6), in initial pictures, the gray-scale value of each pixel is zero, then divides the process of the following two kinds situation:

Situation one, if zero lap, the then correspondence position copying to initial pictures of above-mentioned fortune image region content between fortune image region corresponding to two different independent point targets;

Situation two, if exist overlapping between fortune image region corresponding to two different independent point targets, then uses the image split-joint method based on mutual information to be stitched together in two fortune image regions, and copies to the correspondence position of initial pictures;

The initial pictures obtained after above-mentioned process is imaging results.