A light field imaging system and a light field acquisition method in the terahertz band

Abstract

The present invention discloses an optical field imaging system and an optical field acquisition method in the terahertz band, which include at least one imaging module, at least one light source module, a positioning and adjustment module, and a control and processing module. The imaging module is used to convert the spatial information of the imaging target in the scene into a projected two-dimensional image; the positioning and adjustment module is used to control the position and attitude of the imaging module in space, and the camera optical characteristics including but not limited to the aperture of the diaphragm and the distance between the focal plane and the lens group; the positioning and adjustment module of the optical imaging system is used to achieve precise positioning of the imaging module, realize detailed quantitative exploration and measurement of the complex spatial complex refractive index distribution inside the object, and the application range of the optical field imaging system of the present application is wider than that of relatively simple imaging systems.

Description

Technical Field

[0001] The present invention relates to the fields of computational imaging and terahertz imaging technology, and particularly relates to a light field imaging system and a light field acquisition method in the terahertz band. Background Art

[0002] Light field imaging is a new emerging computational imaging method.

[0003] The definition of light field is "the distribution of light flux in space"; in the field of imaging applications, for the light field in space, we usually describe it in the form of a plenoptic function.

[0004] According to the visual perception mode of the human eye to light, the light field in space can be represented by a seven-dimensional plenoptic function where x, y, z represent the three-dimensional coordinates of any point in space, represents the propagation direction of the light ray, λ represents the wavelength of the light ray, and t represents time. In the case of recording a transient light field with a specific wavelength, λ and t are fixed and unchanged, and the plenoptic function can be simplified to five-dimensional And in the case of ignoring attenuation, the intensity of the "light ray" can be regarded as unchanged along the propagation direction of the light ray and independent of the distance from the observer, and the plenoptic function can be simplified to four-dimensional That is, the set of each "light ray" can be represented by a four-dimensional function representation.

[0005] By introducing new dimensional information, light field imaging technology has greatly broken through the limitations of traditional cameras in imaging ability and imaging flexibility. Compared with the traditional two-dimensional integral imaging method, light field imaging can achieve many imaging applications that the former cannot achieve by extracting and fusing redundant dimensional information in the four-dimensional light field; compared with the more information-rich coherent imaging method, light field imaging does not depend on a harsh laboratory environment, a strict coherent light source and a cumbersome system setup, and only requires relatively simple and integrated equipment to achieve a similar level of information richness.

[0006] Through the post-processing of the four-dimensional light field, the two-dimensional slice reconstruction and reproduction of the four-dimensional light field (i.e., refocusing enhancement, all-in-focus image synthesis, view interpolation), depth estimation, three-dimensional scene measurement and reproduction based on depth estimation, signal-to-noise ratio improvement and super-resolution imaging based on equivalent large aperture synthesis, etc. can be realized.

[0007] Terahertz waves are electromagnetic waves with wavelengths ranging from 3000μm to 30μm and frequencies ranging from 0.1THz to 10THz. Since terahertz waves have good penetrability for dielectrics (such as wood, paper, ceramics, plastics, composite materials, etc.); and because of their low photon energy (0.4 - 41meV), far lower than the ionization threshold, they also have good non-destructiveness for the vast majority of detected objects. Therefore, terahertz band imaging technology is widely used in fields that require perspective imaging and non-destructive testing, such as cultural relic archaeology, biomedicine, industrial inspection, security inspection, etc.

[0008] The imaging targets applying terahertz imaging technology mostly have complex spatial complex refractive index distributions in the terahertz band, that is, spatial refractive index distributions and spatial absorption rate distributions. These distributions are closely related to the attributes of the imaging target such as its shape, state, and properties, and thus are also the main quantitative exploration and measurement targets of terahertz imaging.

[0009] Currently, the imaging methods for objects in the terahertz band mainly include two categories: coherent and non-coherent. Among them, coherent methods include Synthetic Aperture Radar, Computed Tomography, Time-Domain Spectroscopy, etc. Most of them remain in the laboratory stage due to reasons such as large and complex equipment, dependence on laboratory environment, insufficient maturity of component technologies and data processing algorithms; non-coherent methods are mostly traditional integral imaging systems composed of catadioptric optical systems and energy detectors including bolometers, Schottky diodes, CMOS-micro-nano mechanical structures, CMOS-antenna structures, and SiGe heterojunction diodes. Their information richness is much lower than that of coherent imaging methods, and they cannot achieve detailed quantitative exploration and measurement of the complex spatial complex refractive index distribution inside the object. Summary of the Invention

[0010] Aiming at the problems in the above background technology, an important object of the present invention is to provide an optical field imaging system.

[0011] To achieve the above object, the specific technical solution of the present invention is as follows:

[0012] An optical field imaging system in the terahertz band, comprising:

[0013] At least one imaging module, which is used to convert the spatial information in the scene into a projected two-dimensional image at a specific spatial position and attitude and at a specific time; the imaging module includes:

[0014] An imaging lens group for focusing the light energy from the imaging target in space onto the target position;

[0015] A detector array, which is installed at the image plane position conjugate to a certain specific imaging range of the imaging lens group, is fixedly installed and perpendicular to the optical axis of the imaging lens group; it is used to convert the received light energy into a specific digital image signal according to the intensity distribution; and

[0016] A light modulation module, which is installed near the imaging lens group and is fixedly installed relative to the imaging lens group; it is used to modulate the intensity, spectrum and spatial spectrum of the light energy received by the detector array;

[0017] At least one light source module, which is used to provide pulsed or continuous wave illumination with a specific wavelength or spectrum, a specific energy distribution or an illumination pattern for the imaging target, and after carrying information about the imaging target, feeds it back to the imaging module for reception and imaging;

[0018] A positioning and adjustment module, which is used to control the position and attitude of the imaging module in space, as well as the camera optical characteristics including but not limited to the aperture diameter and the distance between the focal plane and the lens group; the positioning and adjustment module includes:

[0019] A position positioning device, which is used to carry and control the precise position of the imaging module in space, that is, the x, y, z positions in the Cartesian coordinate system;

[0020] An attitude positioning device, which is used to carry and control the precise attitude of each camera module in space, that is, the direction and pitch attitude in the Cartesian coordinate system;

[0021] A controllable aperture, which is used to adjust the light passing amount and the light passing aperture of the imaging lens group of the imaging module, and can be completely closed for zeroing the detector of the imaging module;

[0022] A lens group control device, which is used to adjust the relative distance between the imaging lens group and the sensor array in the imaging module;

[0023] A control and processing module, which is respectively connected to the imaging module, the light source module and the positioning and adjustment module, and is used to manipulate the imaging module, the positioning and adjustment module and the light source module through control signals and feedback signals to make them work synchronously and orderly; at the same time, it receives the parallax image information from the imaging module and the parameter information fed back by the positioning and adjustment module, and arranges and reconstructs them to generate a four-dimensional light field accordingly.

[0024] Further, the distance between the imaging lens group and the detector satisfies that the imaging module can clearly and correspondingly focus the points on the imaging target between the corresponding minimum imaging distance and the maximum imaging distance on the detector array.

[0025] Further, the light modulation module includes an attenuation sheet, a filter sheet, a fixed or adjustable spatial light modulation sheet.

[0026] Specifically, in the technical solution of the present invention, the light source module includes:

[0027] A light source for generating terahertz waves with a specific wavelength or spectrum, a specific energy and energy distribution, and continuous waves or specific pulse widths for illuminating an imaging target;

[0028] A collimating and beam expanding optical path for changing the propagation direction, propagation mode, and beam aperture of the terahertz waves generated by the light source so that they can correctly and appropriately illuminate the imaging target, including lenses, mirrors, and parabolic mirror elements; and

[0029] A light source modulation module for changing the light intensity, energy distribution, illumination pattern, and coherence of the terahertz waves generated by the light source, including attenuation sheets, filter sheets, interference components, and beam homogenizer elements.

[0030] Specifically, in the technical solution of the present invention, the control and processing module includes:

[0031] Position and attitude control for controlling the positioning and adjustment module by sending control signals according to a predefined program or user input and receiving feedback, so that the position and attitude of each imaging module are positioned at appropriate positions;

[0032] Detector array control for controlling the integration time and zero setting of the detector array according to a predefined program or user input, as well as the synchronization actions between the detector array, the light source module, and the positioning and adjustment module;

[0033] Aperture control for controlling the action of the controllable aperture according to a predefined program or user input;

[0034] Lens group control for controlling the action of the lens group control device according to a predefined program or user input;

[0035] Data processing and storage for assembling the received parallax images and the corresponding feedback of position and attitude, detector, aperture, and lens group parameters according to rules and generating complete four-dimensional light field information.

[0036] The second object of the present invention is to provide a light field acquisition method for a light field imaging system based on the above terahertz band, and the specific steps are as follows:

[0037] S1. First, place the imaging target within the imaging range of the light field imaging system, and illuminate the imaging target in an appropriate manner and direction with the light source module according to the need; then, determine the light field acquisition parameters according to the size, optical characteristics of the imaging target, and the requirements for post-processing of the light field, that is, the set of positions, attitudes, and optical parameters of all the parallax images included in the acquired light field;

[0038] S2. Then, according to the established acquisition parameters, the control and processing module in the light field imaging system sends control signals to the positioning and adjustment module, controlling the latter to carry all the imaging modules to be positioned at a specified position with a specified attitude and optical parameters. Under the control of the synchronization signal, all the parallax images contained in the required light field information and the parameters attached to each parallax image are acquired in a simultaneous or time-sharing manner.

[0039] In the technical solution of the present invention, in step S2, the position positioning device and the attitude positioning device of the positioning and adjustment module are sequentially connected in series and are respectively fixed to each of the imaging modules. Under the signal control of the positioning attitude control, the position positioning device and the attitude positioning device carry each of the imaging modules to acquire parallax images of the target, that is, a part of the light field information, at a specified position with a specified attitude in a time-sharing or one-time manner. During this period, the controllable aperture controls the aperture of the aperture under the signal of the aperture control, and the lens group control device controls the distance between the lens group and the detector array under the signal of the lens group control.

[0040] In the technical solution of the present invention, the positioning accuracy control of the imaging module includes:

[0041] The spatial positioning accuracy of the position positioning device is higher than half of the size corresponding to each pixel of the detector array of the imaging module on the image plane at the minimum imaging distance of the imaging module, that is where Δl is the positioning error in each dimension, L is the minimum imaging distance, f is the image plane distance, and Δp is the pixel size;

[0042] The attitude positioning accuracy of the attitude positioning device is higher than half of the angular resolution corresponding to each pixel of the detector array of the imaging module in the image space at the maximum imaging distance of the imaging module, that is where Δθ is the attitude angle error in each dimension, f is the image plane distance, and Δp is the pixel size;

[0043] The adjustment capabilities of the position positioning device, the attitude positioning device, the controllable aperture, and the lens group control device of the positioning and adjustment module in terms of the attitude and optical parameters of the imaging module together constitute the imaging range of the entire light field imaging system, that is, the available positions, available attitudes, and effective action distances at which the entire light field imaging system can effectively acquire parallax images.

[0044] In the technical solution of the present invention: during positioning control, described from a mathematical perspective, the imaging module can be abstracted as a pinhole camera. That is, when a coordinate system is established with the camera as the origin and the camera optical axis direction as the z-axis direction, the plane conjugate to the pinhole camera image plane in the object space is called the imaging plane, and the point where the imaging plane intersects the z-axis is called the principal point. A uv rectangular coordinate system is established on the imaging plane with the principal point as the origin; then the projection transformation of the camera from the object space to the image plane satisfies:

[0045]

[0046] where u and v are the coordinates of the image plane, X, Y, and Z are the coordinates of the object plane, and f is the focal length;

[0047] When considering the case where the origin of the detector array is not at the center, the transformation formula becomes:

[0048]

[0049] where u 0 , v 0 is the offset of the sensor coordinate center relative to the principal point.

[0050] Furthermore, when introducing the position and attitude of the camera, it is necessary to transform the obtained light field between the camera coordinate system and the world coordinate system. The transformation formula is:

[0051] X cam = R(X world - C),

[0052] where X cam represents the camera coordinate system, X world represents the world coordinate system, R represents the rotation matrix of the camera, and C represents the displacement matrix of the camera; thus, the parallax collected by the imaging module can be converted into a part of the light field according to the position and attitude information of the camera and the camera parameters.

[0053] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0054] The present invention solves the defect of low richness of incoherent imaging information, uses the positioning and adjustment module of the optical imaging system to achieve precise positioning of the imaging module, and realizes detailed quantitative exploration and measurement of the complex spatial complex refractive index distribution inside the object. Compared with a relatively simple imaging system, the application range of the light field imaging system of the present application is wider. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a structural schematic block diagram of the functional modules of the light field imaging system;

[0056] Figure 2 is a schematic diagram of the imaging module;

[0057] Figure 3 It is a schematic diagram of a light source module;

[0058] Figure 4 It is a schematic diagram of a positioning and adjustment module;

[0059] Figure 5 It is a schematic block diagram of the control and processing module structure. Specific implementation manners

[0060] The following will describe the specific implementation manners of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific implementation manners described herein are only for explaining and understanding the present invention, and are not used to limit the present invention.

[0061] Example 1 is as Figures 1-3 shown, a light field imaging system in the terahertz band, comprising:

[0062] At least one imaging module, which is used to convert the spatial information in the scene into a projected two-dimensional image at a specific spatial position and attitude and at a specific time; the imaging module includes:

[0063] An imaging lens group, which is used to focus the light energy from the imaging target in space on the target position;

[0064] A detector array, the detector array is installed at the image plane position conjugate to a specific imaging range of the imaging lens group, and is fixedly installed and perpendicular to the optical axis of the imaging lens group; it is used to convert the received light energy into a specific digital image signal according to the intensity distribution; and

[0065] A light modulation module, the light modulation module is installed near the imaging lens group, and its installation is fixed relative to the imaging lens group; it is used to modulate the intensity, spectrum and spatial spectrum of the light energy received by the detector array; it includes elements such as an attenuation sheet, a filter sheet, a fixed or adjustable spatial light modulation sheet, etc.;

[0066] For the scenery within the imaging range in space, the light energy from the scenery passes through the aperture of the imaging lens group, and after being focused and transformed by the imaging lens group, it is focused on different points of the sensor array, and the sensor array converts it into a specific digital image signal according to the intensity distribution of the received light energy, thereby completing the acquisition of one view angle in the light field.

[0067] The distance between the imaging lens group and the sensor array, that is, the imaging range where the sensor is conjugate to the imaging lens group, can be continuously and precisely adjusted by the lens adjustment module;

[0068] The acquisition time and integration time of the sensor array can be controlled by a synchronization signal to keep in sync with the light source module and the positioning and adjustment module.

[0069] At least one light source module, which is used to provide pulsed or continuous-wave illumination with a specific wavelength or spectrum, a specific energy distribution, or an illumination pattern for the imaging target, and after carrying information about the imaging target, feeds back to the imaging module for reception and imaging; the light source module includes:

[0070] A light source, which is used to generate terahertz waves with a specific wavelength or spectrum, a specific energy and energy distribution, continuous waves, or specific pulse-width pulses for illuminating the imaging target;

[0071] A collimation and beam expansion optical path, which is used to change the propagation direction, propagation mode, and beam aperture of the terahertz waves generated by the light source so that they can irradiate the imaging target correctly and appropriately, including lenses, mirrors, and parabolic mirror elements; and

[0072] A light source modulation module, which is used to change the light intensity, energy distribution, illumination pattern, and coherence of the terahertz waves generated by the light source, including attenuation sheets, filter sheets, interference components, and beam homogenizer elements.

[0073] The collimated light or divergent light generated by the light source is modulated by the light source modulation module, and then the propagation direction, propagation mode, and beam aperture of the light beam are changed through the collimation and beam expansion optical path, and it irradiates the imaging target in an appropriate way. After interacting with the imaging target, including absorption, refraction, transmission, reflection, and scattering, and carrying information about the imaging target, it is received and imaged by the imaging module. The emission moment of the light source can be controlled by a synchronization signal so as to be synchronized with the imaging module and the positioning and adjustment module.

[0074] A positioning and adjustment module, which is used to control the position and attitude of the imaging module in space, as well as the camera optical characteristics including but not limited to the aperture diameter, and the distance between the focal plane and the lens group; the positioning and adjustment module includes:

[0075] A position positioning device, which is used to carry and control the precise position of the imaging module in space, that is, the x, y, z positions in the Cartesian coordinate system;

[0076] An attitude positioning device, which is used to carry and control the precise attitude of each camera module in space, that is, the direction and pitch attitude in the Cartesian coordinate system;

[0077] A controllable aperture, which is used to adjust the light passing amount and the light passing aperture of the imaging lens group of the imaging module, and can be completely closed for zeroing the detector of the imaging module;

[0078] A lens group control device, which is used to adjust the relative distance between the imaging lens group and the sensor array in the imaging module;

[0079] A control processing module, which is respectively connected to the imaging module, the light source module, and the positioning and adjustment module, is used to manipulate the imaging module, the positioning and adjustment module, and the light source module through control signals and feedback signals to make them work synchronously and orderly; at the same time, it receives the parallax image information from the imaging module and the parameter information fed back by the positioning and adjustment module, and arranges and reconstructs them to generate a four-dimensional light field accordingly.

[0080] Specifically, in the technical solution of the present invention, the control processing module includes:

[0081] Positioning attitude control, which is used to control the positioning and adjustment module by sending control signals to the positioning and adjustment module according to a preset program or user input and receiving feedback, so that the position and attitude of each imaging module are positioned at appropriate positions;

[0082] Detector array control, which is used to control the integration time and zero setting of the detector array according to a preset program or user input, as well as the synchronous actions between the detector array, the light source module, and the positioning and adjustment module;

[0083] Diaphragm control, which is used to control the action of the controllable diaphragm according to a preset program or user input;

[0084] Lens group control, which is used to control the action of the lens group control device according to a preset program or user input;

[0085] Data processing and storage, which is used to assemble the received parallax images and the corresponding positioning attitudes, detector, diaphragm, and lens group parameter feedbacks according to rules and generate complete four-dimensional light field information.

[0086] The acquisition parameters of the light field are input by the user or program into the data processing and storage module, including the spatial positions, attitudes, and camera parameters of each parallax image corresponding to the required light field information. Then, the data processing and storage module converts all parameters into control signals and synchronization signals for positioning attitude control, detector array control, diaphragm control, and lens group control, and sends the signals to the imaging module, the light source module, and the positioning and adjustment module via the software and hardware interface, so that the imaging module, the light source module, and the positioning and adjustment module collect the light field orderly under the control of the signals; after the collected parallax images and the corresponding parameter information are transmitted back to the data processing and storage module via the software and hardware interface, they will be converted into light field slices according to the initial light field acquisition parameters and fused into the required complete light field information.

[0087] Embodiment 2 A method for collecting a light field of a light field imaging system based on the above terahertz band, the specific steps are as follows:

[0088] S1. First, place the imaging target within the imaging range of the light field imaging system, and illuminate the imaging target in an appropriate manner and direction with the light source module according to requirements. Then, determine the acquisition parameters of the light field based on the size, optical characteristics of the imaging target, and requirements for post-processing of the light field, that is, the set of positions, postures, and optical parameters of all the disparity images included in the acquired light field.

[0089] S2. Then, according to the established acquisition parameters, the control and processing module in the light field imaging system sends a control signal to the positioning and adjustment module to control the latter to carry all the imaging modules to be positioned at a specified position with specified postures and optical parameters. Under the control of the synchronization signal, all the disparity images included in the required light field information and the parameters attached to each disparity image are acquired in a simultaneous or time-sharing manner.

[0090] In the technical solution of the present invention, in step S2, the position positioning device and the posture positioning device of the positioning and adjustment module are sequentially connected in series and are respectively fixed to each of the imaging modules. Under the signal control of the positioning and posture control, the position positioning device and the posture positioning device carry each of the imaging modules to acquire the disparity images of the target, that is, a part of the light field information, at the specified position with the specified posture in a time-sharing or one-time manner. During this period, the controllable aperture controls the aperture size under the signal of the aperture control, and the lens group control device controls the distance between the lens group and the detector array under the signal of the lens group control.

[0091] In the technical solution of the present invention, the positioning accuracy control of the imaging module includes:

[0092] The spatial positioning accuracy of the position positioning device is higher than half of the size corresponding to each pixel of the detector array of the imaging module on the image plane at the minimum imaging distance, that is, where Δl is the positioning error in each dimension, L is the minimum imaging distance, f is the image plane distance, and Δp is the pixel size;

[0093] The posture positioning accuracy of the posture positioning device is higher than half of the angular resolution corresponding to each pixel of the detector array of the imaging module in the image space at the maximum imaging distance, that is, where Δθ is the posture angle error in each dimension, f is the image plane distance, and Δp is the pixel size;

[0094] The adjustment capabilities of the position positioning device, the posture positioning device, the controllable aperture, and the lens group control device of the positioning and adjustment module in terms of the posture and optical parameters of the imaging module together constitute the imaging range of the entire light field imaging system, that is, the available positions, available postures, and effective action distances at which the entire light field imaging system can effectively acquire disparity images.

[0095] In the technical solution of the present invention: during positioning control, described from a mathematical sense, the imaging module can be abstracted as a pinhole camera. That is, when a coordinate system is established with the camera as the origin and the camera optical axis direction as the z-axis direction, the plane conjugate to the pinhole camera image plane in the object space is called the imaging plane, and the point where the imaging plane intersects the z-axis is called the principal point. A uv rectangular coordinate system is established on the imaging plane with the principal point as the origin; then the projection transformation of the camera from the object space to the image plane satisfies:

[0096]

[0097] where u and v are the image plane coordinates, X, Y, and Z are the object plane coordinates, and f is the focal length;

[0098] When considering the case where the origin of the detector array is not at the center, the transformation formula becomes:

[0099]

[0100] where u 0 , v 0 is the offset of the sensor coordinate center relative to the principal point.

[0101] Furthermore, when introducing the position and attitude of the camera, it is necessary to transform the obtained light field between the camera coordinate system and the world coordinate system. The transformation formula is:

[0102] X cam = R(X world - C),

[0103] where X cam represents the camera coordinate system, X world represents the world coordinate system, R represents the rotation matrix of the camera, and C represents the displacement matrix of the camera; thus, the parallax collected by the imaging module can be converted into a part of the light field according to the position and attitude information of the camera and the camera parameters.

[0104] In a specific embodiment, this embodiment provides a light field imaging system, which includes an imaging module, a light source module, a positioning and adjustment module, and a control and processing module.

[0105] As Figure 2 shown, in this embodiment, the imaging module and the part of the positioning and adjustment module that controls the imaging module include:

[0106] · The imaging lens group 201 controlled by the lens group control device for position and movement

[0107] · The detector array 202

[0108] · The adjustable aperture diaphragm 203 controlled by the diaphragm control for regulation

[0109] · Spatial light modulation sheet 204

[0110] · Band - pass filter sheet 205

[0111] · Attenuator sheet 206;

[0112] The lens group control device is driven by a stepper motor. The imaging lens group 201 is an optical lens group made of a material with a certain refractive index for terahertz waves, and is used to focus terahertz waves for imaging. The imaging lens group 201 can move and be positioned along the optical axis under the control of the lens group control device, so that the detector array 202 is conjugate to planes at different depths in the object space. The detector array 202 is a planar array photodetector sensitive to the terahertz band, and is used to convert the received terahertz wave signal into an electronic image signal. The adjustable aperture stop 203 is coaxial with the imaging lens group 201 and is located near the imaging lens group 201. It can accurately change the light - passing aperture under the regulation of the aperture control, and is used to adjust the light - passing amount and depth of field of the imaging module. The spatial light modulation sheet 204 is an element with a certain spatial complex refractive index distribution or an adjustable spatial complex refractive index distribution. Using the Fourier transform characteristics of optical lenses, it is used to modulate the received image information in the spatial frequency domain, including but not limited to intensity and phase. The band - pass filter sheet 205 is a uniform thin sheet that is transparent to terahertz waves in a specific wavelength range and opaque to electromagnetic waves in other wavelength ranges. It is located in front of the imaging lens group and is used to filter out stray light and improve the image signal - to - noise ratio. Its passband matches the sensitive wavelength range of the detector array 202. The attenuator sheet 206 is a semi - transparent uniform thin sheet that has a certain absorption rate for terahertz waves in a specific wavelength range. It is located in front of the imaging lens group and is used to adjust the incident light intensity to match the dynamic range and maximum received power of the detector array 202;

[0113] During the imaging process of the imaging module, after the terahertz wave is attenuated by the attenuator sheet 206 and filtered by the filter sheet 205, it is focused by the imaging lens group 201. After being modulated by the aperture stop 203 and the spatial light modulation sheet 204, it forms an image on the detector array 202, and the detector array 202 converts the light energy signal into an image signal. When the imaging module and the positioning and adjustment module have undergone sufficient aberration calibration and geometric calibration, the parallax image output by the imaging module can be considered as an accurate slice of the light field at a specific position.

[0114] As Figure 3 shown, in this embodiment, the light source module includes:

[0115] · Light source 301

[0116] · Diverging concave lens 302

[0117] · Collimating convex lens 303

[0118] · Reflector 304;

[0119] The light source 301 generates a terahertz beam that is approximately collimated and has a small beam size, and its frequency or spectrum matches the sensitive wavelength range of the above-mentioned detector array 202; the diverging concave lens 302 is an optical concave lens made of a material with a certain refractive index for terahertz waves, and is used to diverge the terahertz waves generated by the light source 301 to change the beam diameter; the collimating convex lens 303 is an optical concave lens made of a material with a certain refractive index for terahertz waves, and is used to re-collimate the terahertz waves diverged by the diverging concave lens 302 into an approximately parallel beam to obtain a suitable beam diameter and power density; the reflector 304 is a plane reflector made of a material with a high reflectivity for terahertz waves, and is used to change the direction of the terahertz beam and irradiate the collimated terahertz waves on the imaging target 305; in the light source module, the optical axes of the light source 301, the diverging concave lens 302, and the collimating convex lens 303 coincide; the midpoint of the reflector 304 approximately coincides with the optical axes of the former three, the aperture of the reflector 304 matches the aperture of the collimating convex lens 303, and the focus of the reflector 304 approximately coincides with the virtual focus of the diverging concave lens; the emission of the light source module 301 is controlled by a synchronization signal and emits pulses only when the synchronization signal arrives.

[0120] During the illumination of the light source module, the approximately collimated small-diameter terahertz beam generated by the light source 301 is diverged by the diverging concave lens 302, and then collimated by the collimating convex lens into a terahertz beam with a larger aperture. The collimated and expanded terahertz beam is reflected by the reflector 304 and irradiated on the imaging target 305, and an interaction occurs between the collimated and expanded terahertz beam and the imaging target 305.

[0121] As Figure 4 shown, in this embodiment, the part of the positioning and adjustment module that controls the position and attitude includes:

[0122] · X-axis translation stage 401

[0123] · Y-axis translation stage 402

[0124] · Z-axis translation stage 403

[0125] · Pitch stage 404

[0126] · Rotary stage 405

[0127] · Adapter 406;

[0128] The x-axis translation stage 401, y-axis translation stage 402, and z-axis translation stage 403 are three-dimensionally configured translation stages that are driven by stepper motors for movement and positioning, and can position the load at a specified spatial coordinate position in three dimensions with sufficient accuracy; 404 is a pitching stage that is driven by a stepper motor for movement and positioning, and can adjust the pitching attitude of the positioned load with sufficient accuracy; 405 is a rotary stage that is driven by a stepper motor for movement and positioning, and can adjust the azimuth attitude of the positioned load with sufficient accuracy; in the positioning and adjustment module, the x-axis translation stage 401, y-axis translation stage 402, z-axis translation stage 403, pitching stage 404, and rotary stage 405 are connected to each other in series;

[0129] When the positioning and adjustment module adjusts the position and attitude of the camera, the x-axis translation stage 401, y-axis translation stage 402, and z-axis translation stage 403 calculate the amount of movement according to the conversion between the amount of movement of the translation stage and the spatial coordinates of the world coordinate system in the prior geometric calibration, and position the load at the specified position by moving the translation stages respectively by the corresponding amount of movement; similarly, the pitching stage 404 and the rotary stage 405 calculate the attitude adjustment amount according to the required conversion between the world coordinate system and the camera coordinate system, and make the camera reach the specified attitude through the rotary movements of the pitching stage 404 and the rotary stage 405.

[0130] See Figure 5 , in this example, the control and processing module structure can be divided into three layers according to software, hardware, and functions: the execution layer, the hardware layer, and the application layer.

[0131] · The execution layer is the part outside the control and processing module that specifically implements the light field imaging function. Its characteristic is that it does not carry the generation and transmission of signals, and only converts the control signal into specific optomechanical system actions after receiving the control signal, including the imaging module, the light source module, and the positioning and adjustment module;

[0132] · The hardware layer is the circuit and interface used in the processing and control module for generating, transmitting, and receiving control signals and image data, including the camera control circuit, image acquisition circuit, synchronization circuit, positioning controller, attitude controller, aperture control circuit, and lens group control circuit for control purposes, the USB 2.0, RS-232, and Ethernet interfaces for signal transmission, and the microcomputer for summarizing, processing, and distributing data and control signals;

[0133] · The application layer is the software part that runs on top of the hardware layer and is used to control the hardware layer to generate signals that meet the requirements, including the sensor zeroing program, integration time control program, geometric calibration program, image acquisition and processing program, synchronization signal generation and control program, positioning control program, attitude control program, aperture control program, and lens group control program.

[0134] When the control processing module processes data, first, the user inputs the light field parameters to be collected, and the control program of the application layer converts them into specific collection parameters for the input hardware layer. Then, the microcomputer, which is the main carrier of the application layer in the hardware layer, converts the specific collection parameters into communication signals via USB2.0, RS-232, and Ethernet interfaces and transmits them to other control circuits and synchronization circuits belonging to the hardware layer. Then, each control circuit and synchronization circuit convert the communication signals into specific control signals to control the specific devices in the execution layer to collect specific parallax images. The collected parallax images are also converted into image information by the image acquisition circuit and are transmitted back to the microcomputer in the form of signals through the hardware interface, and then are converted into light field slices and fused into the final light field image by the image acquisition and processing program of the application layer.

[0135] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to multiple fields applicable to the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated and described examples here.

Claims

1. A light field imaging system in the terahertz band, characterized in that, it includes: At least one imaging module for converting the spatial information of the imaging target in the scene into a projected two-dimensional image; The imaging module includes: An imaging lens group for focusing the light energy from the imaging target in space at the target position; A detector array, which is installed at the image plane position conjugate to the specific imaging range of the imaging lens group and is perpendicular to the optical axis of the imaging lens group; for converting the received light energy into a specific digital image signal according to the intensity distribution; and A light modulation module, which is installed near the imaging lens group and is fixed relative to the imaging lens group; for modulating the intensity, spectrum and spatial spectrum of the light energy received by the detector array; At least one light source module for providing pulsed or continuous wave illumination with a specific wavelength or spectrum, specific energy distribution or illumination pattern for the imaging target, and after carrying the information about the imaging target, feeding it back to the imaging module for reception and imaging; A positioning and adjustment module for controlling the position and attitude of the imaging module in space, as well as the camera optical characteristics such as the aperture and the distance between the focal plane and the lens group; the positioning and adjustment module includes: A position positioning device for carrying and controlling the precise position of the imaging module in space, i.e., the position in the Cartesian coordinate system position; An attitude positioning device for carrying and controlling the precise attitude of each camera module in space, that is, the direction and pitch attitude in the Cartesian coordinate system; A controllable aperture for adjusting the light passing amount and the light passing aperture of the imaging lens group of the imaging module, and can be completely closed for zeroing the detector of the imaging module; A lens group control device for adjusting the relative distance between the imaging lens group and the detector array in the imaging module; A control and processing module, which is respectively connected to the imaging module, the light source module and the positioning and adjustment module, for manipulating the imaging module, the positioning and adjustment module and the light source module through control signals and feedback signals to make them work synchronously and orderly; at the same time, receiving the parallax image information from the imaging module and the parameter information fed back by the positioning and adjustment module, and arranging and reconstructing them accordingly to generate a four-dimensional light field; The distance between the imaging lens group and the detector satisfies that the imaging module can clearly and correspondingly focus the points on the imaging target between the corresponding minimum imaging distance and the maximum imaging distance on the detector array; The light source module includes: A light source for generating terahertz waves with a specific wavelength or spectrum, specific energy and energy distribution, continuous wave or specific pulse width pulse for illuminating the imaging target; A collimation and beam expansion optical path for changing the propagation direction, propagation mode and beam aperture of the terahertz waves generated by the light source so that it can correctly and appropriately illuminate the imaging target, including lens, mirror and parabolic mirror elements; and A light source modulation module for changing the light intensity, energy distribution, illumination pattern and coherence of the terahertz waves generated by the light source, including attenuation sheet, filter sheet, interference components and beam homogenizer components.

2. The light field imaging system in the terahertz band according to claim 1, characterized in that, The light modulation module includes an attenuation sheet, a filter sheet, a fixed or adjustable spatial light modulation sheet.

3. A terahertz-band light field imaging system according to claim 1, characterized in that, the control and processing module includes: Position and attitude control, which is used to control the positioning and adjustment module by sending control signals to the positioning and adjustment module according to a predefined program or user input and receiving feedback, so that the position and attitude of each imaging module are positioned at the target position; Detector array control, which is used to control the integration time and zero setting of the detector array according to a predefined program or user input, as well as the synchronous actions between the detector array, the light source module, and the positioning and adjustment module; Diaphragm control, which is used to control the action of the controllable diaphragm according to a predefined program or user input; Lens group control, which is used to control the action of the lens group control device according to a predefined program or user input; Data processing and storage, which is used to assemble the received parallax images and the corresponding feedback of positioning and attitude, detector, diaphragm, and lens group parameters according to rules and generate complete four-dimensional light field information.

4. A light field acquisition method for a terahertz-band light field imaging system according to any one of claims 1-3, characterized in that, the specific steps are as follows: S1. First, place the imaging target within the imaging range of the light field imaging system and illuminate the imaging target with the light source module as needed; then, determine the acquisition parameters of the light field according to the size, optical characteristics of the imaging target, and the requirements for post-processing of the light field, that is, the set of positions, attitudes, and optical parameters of all parallax images included in the acquired light field; S2. Then, according to the predefined acquisition parameters, the control and processing module in the light field imaging system sends control signals to the positioning and adjustment module to control the latter to carry all imaging modules to be positioned at the target position with the required attitude and optical parameters. Under the control of the synchronization signal, all parallax images included in the required light field information and the parameters attached to each parallax image are acquired in a simultaneous or time-sharing manner; In step S2, the position positioning device and the attitude positioning device of the positioning and adjustment module are sequentially connected in series and are respectively fixed to each imaging module; under the signal control of the position and attitude control, the position positioning device and the attitude positioning device carry each imaging module at the target position with the attitude to acquire parallax images of the target in a time-sharing or one-time manner, that is, a part of the light field information; during this period, the controllable diaphragm controls the diaphragm aperture under the signal of the diaphragm control, and the lens group control device controls the distance between the lens group and the detector array under the signal of the lens group control.

5. A light field acquisition method for a terahertz-band light field imaging system according to claim 4, characterized in that, When described mathematically during positioning control, the imaging module can be abstracted as a pinhole camera, that is, when a coordinate system is established with the camera as the origin and the camera optical axis direction as the z-axis direction, the plane conjugate to the pinhole camera image plane in the object space is called the imaging plane, the point where the imaging plane intersects the z-axis is called the principal point, and a uv rectangular coordinate system is established on the imaging plane with the principal point as the origin; then the projection transformation of the camera from the object space to the image plane satisfies: where \(u, v\) are image plane coordinates, \(X, Y, Z\) are object plane coordinates, and \(f\) is the focal length; when considering the case where the origin of the detector array is not at the center, the transformation formula becomes: Among them, u 0 , v 0 is the offset of the detector coordinate center relative to the principal point.

6. The light field acquisition method of the light field imaging system based on the terahertz band according to claim 5, characterized in that, when introducing the position and attitude of the camera, it is necessary to transform the obtained light field between the camera coordinate system and the world coordinate system, and the transformation formula is: X cam =R(X world -C), Among them, X cam represents the camera coordinate system, and X world represents the world coordinate system. R represents the rotation matrix of the camera, and C represents the displacement matrix of the camera. Thus, the parallax collected by the imaging module can be converted into a part of the light field according to the position and attitude information of the camera and the camera parameters.

Images