WO2014106301A1

WO2014106301A1 - Method and apapratus for a single control multi-source active image acquisition system

Info

Publication number: WO2014106301A1
Application number: PCT/CA2014/050002
Authority: WO
Inventors: Abdorreza Heidari
Original assignee: Plurapix, Inc.
Priority date: 2013-01-03
Filing date: 2014-01-03
Publication date: 2014-07-10

Abstract

There is provided a method of image acquisition comprising setting signal shaping parameters for transmission of light via a processor, illuminating an object with the light based on the signal shaping parameters, retrieving measurements resulting from illuminating the object via the processor, and reconstructing an image of the object based on the measurements via the processor; wherein the method is performed using a single control.

Description

METHOD AND APAPRATUS FOR A SINGLE CONTROL

MULTI-SOURCE ACTIVE IMAGE ACQUISITION SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of United States Provisional Application No.

61/748,617 filed January 3, 2013 which is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The disclosure is generally directed at image acquisition and more specifically at a novel method and apparatus for a single control multi-source active image acquisition system.

BACKGROUND TO THE DISCLOSURE

Image acquisition has been studied for many years and there have been many

improvements over the years, however, there are still numerous struggles with this technology. The current challenges of imaging systems include achieving higher signal-to-noise ratios (SNRs) and higher resolutions at given levels of source power and for a given detector quality, over a short acquisition time.

Image acquisition time is frequently encountered as a disabling factor in various current imaging modalities. In conventional imaging systems, these problems are usually addressed by upgrading the hardware being used within the system; by using sources with higher power; using more sensitive detectors, or by using a more sophisticated and complicated imaging apparatus setup. However, this approach may not always be possible or feasible. The desired technology may not be available, or not applicable due to the conditions in which the image is being acquired. Also, the use of upgraded hardware will typically result in a more expensive system.

Therefore, there is provided a novel method and apparatus for a single control multi- source active image acquisition system.

SUMMARY OF THE DISCLOSURE

In this disclosure, a novel method and apparatus for a single control multi-source active image acquisition system is disclosed which employs advanced computational and processing techniques. In one embodiment, the method and apparatus reduces the hardware complexity of the image acquisition system and may increase the imaging quality compared to conventional methods. Furthermore, using the method and apparatus of the disclosure pushes some of the procedures of the imaging setup to the software side, such as calibration of the system which may be done faster and easier than by conventional hardware calibration.

An advantage of the method and apparatus of the disclosure is that the same hardware setup may be customized for different application requirements. Furthermore, using

coding/modulation schemes within the method and apparatus of the disclosure allows the system to acquire more resolvable information from the object in a shorter time. Also by employing advanced demodulation/decoding techniques, higher signal to noise ratios may be achieved.

DESCRIPTION OF THE FIGURES

Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

Figure la is a schematic diagram of an embodiment of apparatus for a single control image acquisition system;

Figure lb is a schematic diagram of another embodiment of apparatus for a single control image acquisition system

Figure 2 is a schematic diagram of a further embodiment of a single control image acquisition system;

Figure 3 is a schematic diagram of a further embodiment of a single control image acquisition system;

Figure 4 is a diagram of binary codes for use with some single control image acquisition systems;

Figure 5 is a flowchart outlining a method of single control image acquisition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosure is directed at a method and apparatus for a multi-source single control active image acquisition system for acquiring images of three-dimensional (3D) objects. In one embodiment, the method and apparatus include coding/modulation and decoding/demodulation techniques to assist in obtaining measurements of light which are then used to reconstruct the image of the object. In operation, data or signals may be generated and used to synchronize the components of the setup, where a) explicit wired or wireless connections are used, or b) implicit connections are used, where the sync data/signals are generated locally by using carrier recovery and tracking methods under a single control.

Turning to Figure la, a schematic diagram of an embodiment of a single control imaging acquisition system is shown. In the current figure, the system 10 is used to capture and then reproduce a 3D image of an object 12. The system 10 comprises a set of light sources 14

(numbered from 1 to M where M is any predetermined number) which are connected to or associated with a set of signal shaping apparatus 16 (also numbered 1 to M) and a set of transmitters 18 (numbered 1 to M). Although shown in a 1 : 1 : 1 relationship between the light sources 14, the signal shaping apparatus 16 and the transmitters 18, the relationship may be in different ratios as would be understood. The transmission of light may be via terahertz, millimeter-waves, infrared or visible lights.

A processor (not shown), such as within a computer 21, is in communication with each of the set of signal shaping apparatus 16 to provide instructions as to how to shape the signal, light or waveform from its associated source 14 for transmission of that shaped waveform towards the object 12 by its associated transmitter 18. This will be described in more detail below.

The system 10 further comprises an apparatus 22 for reception, detection or both of the light after it has interacted with the object 12 and an apparatus for processing and reconstructing 24 which creates an image of the 3D object. In one embodiment, the apparatus for processing and reconstructing 24 is integrated with the processor such that it is part of the computer 21. The computer 21 may further include a display 26 which is used to display the image of the 3D object. The apparatus 22 may communicate with the apparatus for processing 24 via a data acquisition system (DAQ) 28.

Each of the components may be connected either directly or indirectly with each other via a bus which is used to synchronize the data being transmitted. The processor is used to control operation of the system therefore allowing for single control of the entire image acquisition system. The processor may be integrated with the system 10 or may be located remotely but in wireless or wired communication with the system 10.

Although the parts are shown separately in Figure la, it will be understood that a single source 14, a single signal shaping apparatus 16 and a single transmitter 18 may be combined to form a single element 13 such as shown in the system 10 of Figure lb. The system 10 further includes apparatus 22 for detecting the interacted light, a processor 20 including apparatus for reconstructing an image 24 and a display 26. The system 10 may further include a DAQ (not shown).

In the preferred embodiment, the transmitters 18 are located spatially to shine waveforms at the object 12 from different positions and angles, preferably i) on distinct points on a spatial linear grid; ii) on distinct points on a spatial 2D surface grid or iii) on distinct points in a 3D space grid although other orientations may be contemplated.

Turning to Figure 2, another embodiment of a single control system for image acquisition is shown. As with the embodiment of Figure 1, the system 10 is used to assist in obtaining an image of an object 12. In Figure 2, the system 10 includes a set of sources 14, which may be seen as light or signal sources or a combination of both which are capable of transmitting waveforms and a set of transmitters 18 for shining the waveforms towards the object 12. In Figure 2, each signal shaping apparatus 16 may be seen as a coding/modulation apparatus 30.

Also, the system 10 further includes a set of receivers/detectors 22. Each of the set of receivers/detectors 22 is associated with a decoding/demodulation apparatus 32. There is preferably an image reconstruction apparatus 24 which is integrated with the processor 20 that communicates with the set of decoding/demodulation apparatus 32 via a multiplexer 31. As will be understood, the transformation of a signal from analog to digital may be performed either within the processor 20 or the decoding/demodulation apparatus 32.

Turning to Figure 3, yet a further embodiment of a system for image acquisition is shown. The system 10 includes a single source 14 in which its individual channels may be separated via a divider 34 wherein, in one embodiment, individual time slots are divided into separate waveform paths. The waveforms resulting from these divided paths are then transmitted to a set of associated switches 36 (which with the divider 34 may be seen as signal shaping apparatus 16) and then transmitted to a set of transmitters 18 so that the waveforms can be shone at the object. In the current embodiment, the processor 20 controls the set of switches 36 to turn them on or off depending on signal shaping parameters which may be either input from a user or pre-stored with the processor 20. In other words, some of the waveforms may not be transmitted towards the object 12 if their switch 36 is turned off by the processor 20 based on the signal shaping parameters. The system 10 may further include a compressive sensing approach such as those known in the art. Such compressive sensing approaches include, but are not limited to those described in Donoho, "Compressed Sensing," IEEE Transactions on Information Theory, vol. 52, no. 4, pp. 1289-1306, 2006., J. Romberg, "Imaging via compressive sampling," IEEE Signal Processing Magazine, vol. 25, no. 2, pp. 14-20, 2008, or Xu, Zhimin, et al. "Sparse reconstruction of complex signals in compressed sensing terahertz imaging. "Signal Recovery and Synthesis. Optical Society of America, 2009.

The system 10 further includes a detector 22 along with a processing and reconstruction apparatus 24 which may be integrated with the processor 20. Although not shown in this figure, the system 10 may further include a display for displaying the image after it has been constructed or a transmitter (not shown) to send the data or reconstructed image to another location or both.

Turning to Figure 5, a flowchart outlining a method of 3D image acquisition is shown. The method may be used in, but not limited to, stand-off scanning, body scanning or microscopy applications. Firstly, the image acquisition system or apparatus 10 is calibrated 100 as necessary. In one embodiment, the calibration is performed in order to prepare the apparatus for use in a selected operation mode, such as, but not limited to, reflection, transmission or total reflection (ATR). In another aspect of calibration, the sources may be tested to confirm that they are emitting the expected waveform. In yet further embodiments of calibration, the imaging acquisition apparatus may be calibrated by a) conventional calibration of the components and the hardware setup, b) characterization of signal shaping parameters by modelling or computer simulation, c) imaging a known object to extract the unknown system parameters using deconvolution algorithms, d) software calibration by evaluating reconstructed image quality or e) frequent or occasional fine-tuning, by tracking the apparatus parameters.

After calibrating the apparatus, signal shaping parameters may be determined and set 102. Based on input from a user or based on pre-set stored instructions, the processor communicates with the signal shaping apparatus to alter the waveform from the source or sources.

For instance, in the embodiment of Figure 2, the signal shaping apparatus, seen as the coding/modulation apparatus, codes or modulates the signal or light, typically being transmitted in the form of waveforms, from the source(s) before they are transmitted by the associated transmitter. In one example, the coding scheme used may be binary or non-binary, which shapes the amplitude of the source signal as follows:

where m = 0, 1, . . . , M - 1 is the source index, S_m(t) is the signal, C_m(t) is the coding waveform, and X_mft) is the signal to be transmitted.

In the embodiment of Figure 3, at each time slot, the waveform is multiplexed to a subset of M paths from the single source to the multiple transmitters based on whether specific switches (acting as a part of the signal shaping apparatus) are turned on or off.

In another embodiment, the number of time slots is determined and then for each time slot, a set of weighting parameters are created or selected which are to be applied to the light to be transmitted towards the object. The weighting parameters may be selected from a sensing matrix.

In another embodiment, if the signal shaping apparatus is performing a modulation on the waveform, the modulation scheme can be performed using amplitude modulation, frequency modulation or phase modulation. The modulation parameters for each source may be picked to maintain a minimum resolubility among the signals and their spurious images. In amplitude modulation, for example, the frequencies can be calculated as f„ =fo + nAf, where fo is the initial frequency, Δ is the frequency distinction, and « = 0, 1, . . . , N - 1 where N is the number of frequencies required. Alternatively, the modulation parameters for each source may be picked to facilitate the generation of the modulating local oscillators from a base frequency, e.g., by using a frequency synthesizer.

In the case of amplitude modulation, the modulated signal S'_m(t) may be created in a manner such as follows: S'_m(t)=S_m(t) cos(F_m(t)+ θ(0), where frequencies F_m,m=0..M-l are a permutation of the frequencies and F_n,n=0.. M-l, and θ(0) is a constant number.

In yet a further embodiment, such as with the embodiment of Figure 2, a

modulation/coding scheme may be applied to each source such as i) to optimize the desired received or interacted light signals compared to the interference signals by, for example, using an orthogonal set of binary codes (such as the sample set of four such codes shown in Figure 4, ii) to optimize the desired received signals in the presence of noise, e.g., by using signal shaping methods in time domain or frequency domain, or iii) to facilitate the synthesis of the encoders by, for example, binary codes that can be implemented by using a network of on-off switches on the path of the signal. In an embodiment, for use with the apparatus of Figure 3, an algorithm may be included which associates the waveforms in individual time slots with specific transmitters.

After the signal has been shaped, the object is illuminated 104 via the transmission of the shaped waveform or waveforms via the set of transmitters. The transmitted light interacts with the object in such a manner which includes, but is not limited to, reflection off the object, transmission through the object or scattering. The resulting light, or interacted light is then received or detected 106 by the receiving apparatus in the form of measurements. The measurement or measurements that are received are then translated into digital signals 108 via a data acquisition process and then stored or transmitted to the processor.

For instance, in the embodiment of Figure 2, the interacted light that is received at the different receivers, either coherently or incoherently, is then demodulated or decoded in order to produce the measurements so that the digital signals may be calculated. The demodulation and/or decoding of the signals may effectively resolve several parallel imaging channels which results in shorter acquisition times. In the embodiment of Figure 3, the interacted light is detected and then measurements are produced and then transmitted as digital signals by the DAQ to the processor or apparatus for reconstruction 24.

In another embodiment, such as for the system of Figure 3, the received signals are recombined to remove the effect of weighting coefficients via linear algebra calculations whereby the linear algebra calculations may include matrix inversion or a least squares algorithm.

In some embodiments, a superposition of the waveforms is detected, coherently or incoherently.

If the interacted waveform is received coherently, the measurements are directed at amplitude and/or phase of the interacted waveform that is received. If the interacted waveform is received incoherently, the measurements are directed at an intensity of the interacted waveform received. These measurements may then be translated into digital signal for the apparatus for reconstruction 24.

After receiving the digital signals, a 3D image based on the measurements is

reconstructed 110. The image reconstruction may be performed in various ways such as, but not limited to, a) extraction of the depth information, e.g., by using the time of arrival method, b) reconstruction of 3D images of the object, e.g., from the multiple view images acquired, c) reconstruction of a higher resolution image by using the geometrical information from the imaging setup, and using several lower resolution images acquired from the proposed system, or d) reconstruction of images showing spectral information as the fourth dimension. Also by using advanced signal processing techniques, including image fusion techniques such as super- resolution methods, the image resolution can be improved, and/or higher signal to noise ratios are achieved which decreases the required power level of the source(s) or the required sensitivity of the detector(s) used in the imaging system.

If the embodiment being used is one where an algorithm associates the time slot waveforms and the transmitters, the reconstruction of the image may also use this information to produce an image of the object when enough measurements are available. To minimize the number of required measurements or digital signals, a known compressive sensing approach may be employed such as disclosed above with respect to Figure 3. Furthermore, the image reconstruction may benefit from using compressive sensing recovery techniques.

The apparatus may then be re-calibrated 112 based on the measurements received, the digital signals produced, on the reconstructed image or by any means as described earlier in 100.

The apparatus may then be shut down if the user is finished with image acquisition or the method may be re-engaged by inputting new signal shaping parameters or by selecting the same signal shaping parameters and returning to 102.

An advantage of the current system is that the apparatus can work off-line, on-line, or for live (video) imaging.

The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.

Claims

What is Claimed is:

1. A method of image acquisition comprising:

setting signal shaping parameters for transmission of light via a processor;

illuminating an object with the light based on the signal shaping parameters;

retrieving measurements resulting from illuminating the object via the processor; and reconstructing an image of the object based on the measurements via the processor wherein the method is performed using a single control element.

2. The method of Claim 1 further comprising, before setting signal shaping parameters, determining calibration parameters for the signal shaping parameters.

3. The method of Claim 2 further comprising:

fine-tuning the calibration parameters based on the measurements.

4. The method of Claim 1 wherein retrieving measurements comprises:

receiving light resulting from interaction with illuminating the object; and translating received light into measurements

5. The method of Claim 4 wherein the light is received coherently or incoherently.

6. The method of Claim 5 wherein setting signal shaping parameters comprises:

selecting a waveform; and

coding or modulating the waveform to serve as light for illuminating the object.

7. The method of Claim 6 wherein reconstructing an image comprises:

demodulating or decoding the measurements into parallel imaging channels; and processing the image channels to producing the image.

8. The method of Claim 1 wherein setting signal shaping parameters comprises:

determining number of sources of light; and for each time slot, applying a set of weighting parameters to the light to be transmitted towards the object.

9. The method of Claim 8 further comprising:

for each time slot, dividing light into an arbitrary number of separate paths to be transmitted toward the object.

10. The method of Claim 8 wherein for each time slot, the weighting parameters are selected from a sensing matrix.

11. The method of Claim 8 further comprising:

recombining the received signals and collectively removing the effect of the weighting coefficients via linear algebra calculations.

12. The method of Claim 11 wherein the linear algebra calculations are matrix inversion or a least squares algorithm.

13. The method of Claim 8 further comprising:

reconstructing an image from the received signals using compressive sensing recovery techniques.

14. The method of Claim 1 wherein illuminating the object comprises:

transmitting light via terahertz, millimeter-waves, infrared or visible lights.

15. Apparatus for acquiring an image of an object comprising:

a set of transmitters for transmitting light signals towards the object;

a set of receivers for determining measurements based on received interacted light from the object; and

a single processor for controlling parameters of the light being transmitted towards the object, developing a set of data based on the measurements from the received interacted light and developing the image of the object based on the set of data.

16. The apparatus of Claim 15 wherein the set of transmitters are coded or modulated light sources.

17. The apparatus of Claim 15 wherein the processor comprises a data acquisition system (DAQ) for translating the measurements to the set of data.

18. The apparatus of Claim 17 wherein the set of data is used by the processor to develop the image.