CN104156908A - High time resolution frequency domain transient imaging method - Google Patents

Abstract

The invention discloses a high time resolution frequency domain transient imaging method. The high time resolution frequency domain transient imaging method includes the following steps: (1) collecting an image set Ix,y(f,phi) on a monitored object through a modulation imaging system; (2) extracting a fundamental wave image and a harmonic wave image Inx,y(nf) from the image set Ix,y(f,phi) with the frequency f; (3) conducting amplitude and phase correction on the fundamental wave image and the harmonic wave image Inx,y(nf); (4) forming a frequency spectrum image set Ipx,y(f) through the fundamental wave image and the harmonic wave image Inx,y(nf) which are corrected already, and conducting Fourier transformation along the frequency f of the frequency spectrum image set to obtain a transient image ix,y(t). According to the high time resolution frequency domain transient imaging method, higher harmonic components are extracted from collected image data with the limited working frequency, information with the higher frequency is obtained, and the time resolution of the transient image is accordingly improved.

Description

The frequency domain transient state formation method of high time resolution

Technical field

The present invention relates to optics and computer vision field, particularly a kind of frequency domain transient state formation method of high time resolution.

Background technology

For general imaging system, the light velocity can be thought infinitely-greatly, and therefore traditional images record is the photoresponse of the object under the stable condition of illumination.But the light transient response of object has comprised more information.The technology of the information of the light transient response of acquisition target is called transient state imaging.A kind of method of transient state imaging is to adopt superfast camera, and needs ultra-short pulse source.This method belongs to time domain acquisition scheme, and its temporal resolution depends on the image taking speed of camera.Shortcoming for adopted hypervelocity imaging system system and light source very expensive, and gatherer process complexity is very consuming time.Another kind method is to adopt modulation imaging system, required system is identical with TOF (flight time) depth camera principle, difference is that depth camera adopts the pulse of fixed frequency to carry out imaging, and transient state imaging modulation imaging system used need to be carried out respectively imaging by multiple frequencies.This method belongs to frequency domain acquisition scheme, and the data that imaging system gathers in each frequency of operation are exactly the frequency spectrum in this frequency of transient images, by Fourier transform and relevant denoise algorithm or adopt optimization method can solve transient images.The temporal resolution of frequency domain transient state imaging depends primarily on the frequency of operation of modulation imaging system.Due to the restriction of hardware system, modulation imaging system can only be operated in limited frequency range, and this has limited the temporal resolution of the transient images obtaining.

Summary of the invention

To the object of the invention is to be modulated into the limited lower technological deficiency of temporal resolution that causes transient images of frequency range as system works in order overcoming in prior art, to have invented a kind of frequency domain transient state formation method of high time resolution.

For solving the problems of the technologies described above, the invention provides a kind of frequency domain transient state formation method of high time resolution, the method comprises the following steps: 1) by modulation imaging system, measurand is gathered to a picture group image set I _x,y(f, φ); 2) the described image set I that is f from frequency _x,yin (f, φ), extract first-harmonic image and harmonic wave image I ⁿ _x,y(nf); 3) to described first-harmonic image and described harmonic wave figure I ⁿ _x,y(nf) as the correction of carrying out amplitude and phase place; 4) by described first-harmonic image and described harmonic image I after proofreading and correct ⁿ _x,y(nf) composition spectrogram image set I ^p _x,y(f), then do Fourier transform along the frequency f of described spectrogram image set and obtain transient images i _x,y(t).

In technique scheme, step 1) described in modulate imaging system and at least comprise a signal generator, a light source and an imaging system.

In technique scheme, step 1) described in by modulation imaging system, measurand is gathered to the image set I that a class frequency is f _x,ythe step of (f, φ) is: a) described in described signal generator control, light source is with frequency f transmit square waves signal, and the shutter of controlling described imaging system is with same frequency imaging; B) image that the phase differential that gathers the control signal of the control signal of described light source and the shutter of described imaging system obtains while being φ and the image that obtains of φ-90 ° form described image set $I_{x,y}(f,\mathrm{\φ})=I_{x,y}^r(f,\mathrm{\φ})+j{I}_{x,y}^i(f,\mathrm{\φ}),$ Wherein j is imaginary symbols.

In technique scheme, step 1) described in modulate imaging system select Selecting phasing that frequency range from low to high selects frequency of operation uniformly-spaced and from 0 to 2 π uniformly-spaced phase place measurand is gathered to image.

In technique scheme, step 2) in the image set I that is f from described frequency _x,yin (f, φ), extract first-harmonic image and harmonic wave image I ⁿ _x,y(nf) step is:

${I^n}_{x,y}\left(\mathrm{nf}\right)=\frac{2}{K}\underset{k=0}{\overset{K}{\mathrm{\Σ}}}{I}_{x,y}(f,k{\mathrm{\φ}}_s)\cos \left(\frac{2\mathrm{\πnk}}{K}\right).$

In technique scheme, step 3) in to described first-harmonic image and described harmonic wave figure I ⁿ _x,y(nf) as before carrying out the correction of amplitude and phase place, first described modulation imaging system is demarcated, the steps include:

A) choose the diffuse reflector of a surface uniform, before being placed on described modulation imaging system;

B) described diffuse reflector is carried out to data acquisition, obtain one group of image C _x,y(f, φ);

C) adopt parameterized model $C_{x,y}(f,\mathrm{\φ})=\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}{A}^n\left(\mathrm{nf}\right)\exp \{-j[\mathrm{n\φ}-{\mathrm{\φ}}_0^n\left(\mathrm{nf}\right)\left]\right\}$ Matching obtains parameter A ⁿ(nf) and

In technique scheme, step 4) by described first-harmonic image and described harmonic image I after proofreading and correct ⁿ _x,y(nf) composition spectrogram image set I ^p _x,y(f), in step, if a Frequency point has multiple image, retain the image of first-harmonic image or minimum subharmonic; If a Frequency point does not have image, supply the image of this Frequency point with amplitude linear interpolation and linear interpolation of phase.

The present invention has following beneficial effect: the frequency domain transient state formation method of high time resolution of the present invention, from the view data of the limited frequency of operation that collects, extract higher harmonic components, obtain the information of higher frequency, thereby improve the temporal resolution of transient images.

Below by drawings and Examples, technical scheme of the present invention is described in further detail.

Brief description of the drawings

Accompanying drawing is used to provide a further understanding of the present invention, and forms a part for instructions, for explaining the present invention, is not construed as limiting the invention together with embodiments of the present invention.In the accompanying drawings:

Fig. 1 is that the present invention is modulated into picture system schematic;

Fig. 2 is the frequency domain transient state formation method process flow diagram of high time resolution of the present invention.

Embodiment

Below in conjunction with accompanying drawing, a specific embodiment of the present invention is described in detail, but is to be understood that protection scope of the present invention is not subject to the restriction of embodiment.

Unless separately there is other clearly to represent, otherwise in whole instructions and claims, term " comprises " or its conversion was stated being understood to include as " comprising " or " including " etc. element or ingredient, and do not get rid of other element or other ingredient.

As shown in Figure 1, the invention provides a kind of modulation imaging system, this system at least comprises: a signal generator, a light source and an imaging system;

As shown in Figure 2, for utilizing the frequency domain transient state formation method process flow diagram of the above-mentioned high time resolution that is modulated into picture System Implementation, the method comprises the following steps:

Step S100: measurand is gathered to a picture group image set I by modulation imaging system _x,y(f, φ), wherein, f is frequency of operation, φ is adjustable phase;

More specifically, first signal generator control light source is with frequency f transmit square waves signal, and the shutter of controlling imaging system is with same frequency imaging; If gather the image obtaining when the phase differential of the control signal of the control signal of light source and the shutter of imaging system is φ if the image obtaining while gathering the phase differential of the control signal of the control signal of light source and the shutter of imaging system and be φ-90 ° therefore the image set, collecting is j is imaginary symbols; Wherein, to select frequency range from low to high to select uniformly-spaced frequency of operation (be frequency of operation f=nf to this modulation imaging system _s, f ∈ [f _l, f _h], wherein n is positive integer, f _sfor frequency interval, f _l, f _hbe respectively minimum and the maximum modulating frequency of modulation imaging system) and the Selecting phasing of from 0 to 2 π uniformly-spaced phase place (be φ=m φ _s, φ _sfor phase intervals, m=0,1 ..., K, K=2 π/φ _s) measurand is gathered to image.

Step S102: the described image set I that is f from frequency _x,yin (f, φ), extract first-harmonic image and harmonic wave image I ⁿ _x,y(nf), wherein n is positive integer;

Wherein, the image set I that is f from frequency _x,yin (f, φ), extract first-harmonic image and harmonic wave image I ⁿ _x,y(nf) concrete grammar step is:

${I^n}_{x,y}\left(\mathrm{nf}\right)=\frac{2}{K}\underset{k=0}{\overset{K}{\mathrm{\Σ}}}{I}_{x,y}(f,k{\mathrm{\φ}}_s)\cos \left(\frac{2\mathrm{\πnk}}{K}\right).$

Step S104: to first-harmonic image and harmonic wave figure I ⁿ _x,y(nf) as the correction of carrying out amplitude and phase place;

Before proofreading and correct, first demarcate (for a modulation imaging system, demarcate and only need to carry out once) to being modulated into as system, obtain the first-harmonic of light signal and the amplitude A of harmonic wave under each frequency of operation ⁿand phase shift (nf) then by I ⁿ _x,y(nf) divided by the step of demarcating is:

1) choose the diffuse reflector of a surface uniform, before being placed on modulation imaging system;

2) diffuse reflector is carried out to data acquisition, obtain one group of image C _x,y(f, φ);

3) adopt following parameterized model matching to obtain parameter A ⁿ(nf) and

$C_{x,y}(f,\mathrm{\φ})=\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}{A}^n\left(\mathrm{nf}\right)\exp \{-j[\mathrm{n\φ}-{\mathrm{\φ}}_0^n\left(\mathrm{nf}\right)\left]\right\}.$

Step S106: by first-harmonic image and harmonic wave image I after proofreading and correct ⁿ _x,y(nf) composition spectrogram image set I ^p _x,y(f), then do Fourier transform along the frequency f of spectrogram image set and obtain transient images i _x,y(t);

By proofread and correct after first-harmonic image and harmonic wave image I ⁿ _x,y(nf) composition spectrogram image set I ^p _x,y(f), in process, if a Frequency point has multiple image, retain the image of first-harmonic image or minimum subharmonic; If a Frequency point does not have image, supply the image of this Frequency point with amplitude linear interpolation and linear interpolation of phase, finally obtaining frequency interval is f _sspectrogram image set I ^p _x,y(f).

The frequency domain transient state formation method of high time resolution of the present invention extracts higher harmonic components from the view data of the limited frequency of operation that collects, obtains the information of higher frequency, thereby improves the temporal resolution of transient images.

The frequency domain transient state formation method of embodiment of the present invention high time resolution is carried out to instance analysis below, be specially the example that an object is carried out to transient state imaging, step is as follows:

Step 200: the frequency of operation 5MHz～165MHz of modulation imaging system is set, interval f _s=1MHz, phase place 0～π, interval φ _s=pi/2 00, collects one group of image I _x,y(f, φ).

Step 202: the image set I that is f for frequency _x,y(f, φ), extracts first-harmonic image and harmonic image;

${I^n}_{x,y}\left(\mathrm{nf}\right)=\frac{2}{K}\underset{k=0}{\overset{K}{\mathrm{\Σ}}}{I}_{x,y}(f,k{\mathrm{\φ}}_s)\cos \left(\frac{2\mathrm{\πnk}}{K}\right).$

Because higher hamonic wave amplitude is less, only select 3 subharmonic, the maximal value of n is 3.

Step 204: with calibrating parameters to first-harmonic image and harmonic wave correct image;

${I^n}_{x,y}\left(\mathrm{nf}\right)={I^n}_{x,y}\left(\mathrm{nf}\right)/\left\{A^n\left(\mathrm{nf}\right)\exp \right[{\mathrm{\φ}}_0^n\left(\mathrm{nf}\right)\left]\right\}.$

Step 206: with proofread and correct after first-harmonic image become spectrogram image set I with harmonic wave image sets ^p _x,y(f), frequency interval is f _s=1MHz.Wherein 5～165MHz frequency range adopts first-harmonic image, and 166～330MHz frequency range adopts second harmonic image, and 331～495MHz frequency range adopts third harmonic image.Non-existent image in 0～5MHz frequency range and 166～495MHz frequency range, supplies by amplitude linear interpolation and linear interpolation of phase.

Step 208: reconstruct transient images i _x,y(t)=FFT[I ^p _x,y(f)].

Finally it should be noted that: above embodiment is only in order to illustrate the present invention and unrestricted technical scheme described in the invention; Therefore, although this instructions has been described in detail the present invention with reference to each above-mentioned embodiment,, those of ordinary skill in the art should be appreciated that still and can modify or be equal to replacement the present invention; And all do not depart from technical scheme and the improvement thereof of the spirit and scope of the present invention, it all should be encompassed in claim scope of the present invention.

Claims (7)

1. a frequency domain transient state formation method for high time resolution, is characterized in that, comprises the following steps:

1) by modulation imaging system, measurand is gathered to a picture group image set I _x,y(f, φ);

2) the described image set I that is f from frequency _x,yin (f, φ), extract first-harmonic image and harmonic wave image I ⁿ _x,y(nf);

3) to described first-harmonic image and described harmonic image I ⁿ _x,y(nf) carry out the correction of amplitude and phase place;

4) by described first-harmonic image and described harmonic image I after proofreading and correct ⁿ _x,y(nf) composition spectrogram image set I ^p _x,y(f), then do Fourier transform along the frequency f of described spectrogram image set and obtain transient images i _x,y(t).

2. the frequency domain transient state formation method of high time resolution according to claim 1, is characterized in that step 1) described in modulate imaging system and at least comprise a signal generator, a light source and an imaging system.

3. the frequency domain transient state formation method of high time resolution according to claim 2, is characterized in that step 1) described in by modulation imaging system measurand is gathered to a picture group image set I _x,ythe step of (f, φ) is:

A) described in described signal generator control, light source is with frequency f transmit square waves signal, and the shutter of controlling described imaging system is with same frequency imaging;

B) image that the phase differential that gathers the control signal of the control signal of described light source and the shutter of described imaging system obtains while being φ and the image that obtains of φ-90 ° form described image set $I_{x,y}(f,\mathrm{\φ})=I_{x,y}^r(f,\mathrm{\φ})+j{I}_{x,y}^i(f,\mathrm{\φ}),$ Wherein j is imaginary symbols.

4. the frequency domain transient state formation method of high time resolution according to claim 1, it is characterized in that step 1) described in modulate imaging system select Selecting phasing that frequency range from low to high selects frequency of operation uniformly-spaced and from 0 to 2 π uniformly-spaced phase place measurand is gathered to image.

5. the frequency domain transient state formation method of high time resolution according to claim 1, is characterized in that step 2) in the image set I that is f from described frequency _x,yin (f, φ), extract first-harmonic image and nth harmonic image I ⁿ _x,y(nf) step is:

${I^n}_{x,y}\left(\mathrm{nf}\right)=\frac{2}{K}\underset{k=0}{\overset{K}{\mathrm{\Σ}}}{I}_{x,y}(f,k{\mathrm{\φ}}_s)\cos \left(\frac{2\mathrm{\πnk}}{K}\right).$

6. according to the frequency domain transient state formation method of the high time resolution described in claim 1-5 any one, it is characterized in that step 3) in to described first-harmonic image and described harmonic image I ⁿ _x,y(nf) before carrying out the correction of amplitude and phase place, first described modulation imaging system is demarcated, the steps include:

A) choose the diffuse reflector of a surface uniform, before being placed on described modulation imaging system;

B) described diffuse reflector is carried out to data acquisition, obtain one group of image C _x,y(f, φ);

C) adopt parameterized model $C_{x,y}(f,\mathrm{\φ})=\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}{A}^n\left(\mathrm{nf}\right)\exp \{-j[\mathrm{n\φ}-{\mathrm{\φ}}_0^n\left(\mathrm{nf}\right)\left]\right\}$ Matching obtains parameter A ⁿ(nf) and

7. the frequency domain transient state formation method of high time resolution according to claim 1, is characterized in that step 4) by described first-harmonic image and described harmonic image I after proofreading and correct ⁿ _x,y(nf) composition spectrogram image set I ^p _x,y(f), in step, if a Frequency point has multiple image, retain the image of first-harmonic image or minimum subharmonic; If a Frequency point does not have image, supply the image of this Frequency point with amplitude linear interpolation and linear interpolation of phase.