Special issue-Computational optical imaging technology and application
2019, 48(6): 603001.
doi: 10.3788/IRLA201948.0603001
Spectral measurement technology has been widely used in non-destructive test, geological prospecting, agriculture and many other fields, and the related technology and devices have achieved great progress in recent years. So spectral measurement technology has developed rapidly in recent years. Based on practical application requirements, the development history of spectral measurement technology was introduced comprehensively and the main spectral measurements including traditional, computational and multiplexing were summarized. The theory and implementation of computational tomography, compressive sensing, Fourier transform, Hadamard transform were introduced in detail and corresponding advantages and disadvantages were pointed out. At last, the problems that need to be solved urgently in spectral measurement technology were analyzed and summarized, and the future development of spectral measurement methods was prospected.
2019, 48(6): 603002.
doi: 10.3788/IRLA201948.0603002
Imaging at non-visible wavebands is one of the challenges in optical imaging. As a novel computational imaging technique, single-pixel imaging based on spatial light modulation is able to obtain spatial information of object via a non-spatially-resolving detector. Thus, single-pixel imaging technique is a potential approach to the challenge of imaging at non-visible wavebands. In recent years, Fourier single-pixel imaging is demonstrated to be able to offer high-quality and high-efficiency image acquisition. Since proposed in 2015, Fourier single-pixel imaging technique has been extended a series of techniques ranging from two-dimensional imaging to three-dimensional imaging, from mono-chromatic imaging to true-color imaging, from static imaging to dynamic imaging, from single-modality imaging to multi-modality imaging, and from photography to microscopy. The principle and related applications of Fourier single-pixel imaging were reviewed. Some challenging problems and prospects of the technique were also discussed.
2019, 48(6): 603003.
doi: 10.3788/IRLA201948.0603003
Unlike a digital cameras using a photodetector array to capture images, single-pixel imaging reconstructs images by sampling a scene with a series of masks and associating the knowledge of these masks with the corresponding intensity measured with a single-pixel detector. Though not performing as well as digital cameras in conventional visible imaging, single-pixel imaging has been demonstrated to be advantageous in unconventional applications, such as multi-wavelength imaging, terahertz imaging, X-ray imaging, and three-dimensional imaging. The developments and working principles of single-pixel imaging were reviewed, a mathematical interpretation was given, and the key elements were analyzed. The research works of three-dimensional single-pixel imaging and their potential applications were further reviewed and discussed.
2019, 48(6): 603004.
doi: 10.3788/IRLA201948.0603004
Single-pixel imaging aims to record the target scene information via a single element detector. For its high sensitivity and wide range of spectrum response, single-pixel imaging is attracting a lot of attentions. Based on the coded acquisition and decoded reconstruction of high dimensional optical signal, single-pixel imaging can meet the demanding requirements in some challenging cases. The research background of single-pixel imaging was firstly introduced, and its imaging principle and reconstruction algorithms were briefly described. Then, from the perspective of coding and decoding of optical information, the current researches and advanced technologies were systematically reviewed. Besides, the existing problems in single-pixel imaging, and its future extensions and potential applications were discussed.
2019, 48(6): 603005.
doi: 10.3788/IRLA201948.0603005
Light scattering is a common phenomenon in nature. How to realize high resolution imaging through turbid media is an important problem to be solved urgently in the field of optical imaging. In early studies, multiple light scattering has been regarded as a barrier in imaging through haze, cloud, biological tissue and other complex media. However, recent studies have shown that scattering is not the basic limitation of imaging:photons still contain a lot of information after multiple scattering. In order to provide insight into how new computational optical techniques can address the issues of multiple light scattering, the recent progress of scattering imaging method based on wavefront shaping, speckle correlation and deep learning was summarized. The latest research shows that, wavefront shaping technology can achieve fast optical focusing inside dynamic scattering medium with high resolution; speckle correlation method can realize non-invasive imaging by single-shot speckle pattern; deep learning is able to recover the object hidden behind the white polystyrene plate with optical thickness of 13.4.
2019, 48(6): 603006.
doi: 10.3788/IRLA201948.0603006
The underwater imaging could be severely degraded by the particles in the water due to the backscatter veiling and signal attenuation. The polarimetric image recovery method is one of the most effective way to enhance the quality of underwater imaging. Based on the polarization property, the polarimetric method can separate the target intensity from the backscattering, estimate the intensity of backscattering and medium transmittance, and then realize clear imaging. In recent years, polarimetric imaging technique has been applied to many fields more efficiently and extensively, such as underwater image restoration and target recognition, etc. As an intersection of optical imaging technique and image processing technique, the polarimetric recovery method for image restoration has aroused a wide concern and gained fruitful research results. In this paper, we mainly introduced the basic principle of underwater image restoration technique based on polarimetric imaging and the methods of polarization information processing. We also reviewed the recent advances of representative improved approaches in underwater image restoration technique based on polarimetric imaging.
2019, 48(6): 603007.
doi: 10.3788/IRLA201948.0603007
Quantitative Phase Microscopy (QPM), which combines phase imaging and optical microscopy, has been acting as a fast, non-destructive, and high-resolution methodology to measure the 3D morphology of reflective samples, as well as the inner structure or the refractive index of transparent samples. Similar to other diffraction-limited imaging systems, QPM suffers from the contradiction between spatial resolution and field of view (FOV). Therefore, how to achieve high spatial resolution in a large FOV has attracted a lot of attentions in the field of optical microscopy. In recent years, people utilized off-axis illumination, speckle illumination, structural illumination, and sub-pixel technology to synthesize a larger numerical aperture (SNA), and consequently enhanced the resolution of QPM. The resolution enhancement technologies of QPM were reviewed in this paper. The advantages and limitations of different methods were analyzed.
2019, 48(6): 603008.
doi: 10.3788/IRLA201948.0603008
As an interference imaging method, digital holography (DH) can accurately record the phase information of objects, and has the advantages of fast, non-destructive and three-dimensional imaging. It is widely used in the field of biological imaging and materials science. Like other optical imaging methods, DH also faces the problem that the resolution and the field of view(FOV) are mutually constrained, resulting in limited spatial bandwidth product(SBP). To solve this problem, researchers proposed methods such as computational illumination, computational modulation, and computational probing to extend SBP by sacrificing other degrees of freedom(such as time and polarization) of the imaging system. This paper firstly reviews the theoretical analysis of information capacity of an optical system. On this basis, we systematically summarize the high-resolution and large-FOV digital holographic imaging technology in recent years, introduce the principle and implementation of oblique illumination, structured illumination, random modulation illumination, multi-position synthetic aperture and pixel super-resolution method for resolution enhancement, and angle multiplexing method for FOV extension, and make a comparative study. The potential ways to improve resolution and expand FOV are also prospected.
2019, 48(6): 603009.
doi: 10.3788/IRLA201948.0603009
Wide field-of-view (FOV) and high-resolution is one of the goals of optical microscopy. However, limited by the optical design in traditional optical microscopes, the space bandwidth product (SBP) is generally in the order of megapixels, and thus, high-resolution and wide FOV cannot be achieved at the same time. On the other hand, complex optical systems have also made microscopes increasingly expensive, cumbersome, complex and difficult to maintain, greatly limiting their promotion and application. Lensfree on-chip microscopy is a new computational imaging technology:without the imaging lens to focus, the sample is directly attached to the imaging sensor to record the diffraction patterns and the object information can be achieved with the corresponding reconstructed method. Due to its wide FOV, high-resolution, label-free detection, low-cost, perfect portability and three-dimensional (3D) imaging, the lensfree on-chip microscope is expected to expand the boundaries of traditional microscopic imaging technology and becomes a new type of fast, point-of-care testing (POCT) tool. In this paper, a review was given to introduce the basic principles, experimental systems, reconstruction methods and applications of lens-free imaging. Finally, the changeling problems as well as future research directions were also discussed.
The technique and application developments of the deformation and displacement measurements based on the digital holography(DH, including the digital speckle interferometry) was reviewed. Because of advantages of high accuracy, non-invasive, full-field and dynamic measurement, DH became one of the most important technique for deformation and displacement measurement. In recent years, the development of DH technique was mainly in the following aspects. Firstly, deformation measurement was developed from one-dimensional measurement to multi-dimensional measurements. Especially, simultaneous deformation measurements in three dimensions was the focus of this domain. Secondly, since curved objects were common in practice. However, in-plane and out-of-plane deformation were the main concern for curved object, which needed the 3D shape information of the curved objects. Thus, for curved objects, simultaneous 3D shape and deformation measurements were studied. Thirdly, to further extend the field of view and the depth of the measurement, techniques based on long wavelength and long distance were explored. Furthermore, measurements based on DH technique progressed from engineering domain towards biomedical domain to facilitate deeper researches in biomedical domain. Meanwhile, various application improvements of deformation measurement based on DH technique were covered in this review.
2019, 48(6): 603011.
doi: 10.3788/IRLA201948.0603011
Coherent diffraction imaging(CDI) is a lensless computational imaging technique, which reconstructs the amplitude and phase of an object directly from diffraction intensity measurement by solving the phase problem using iterative algorithms. CDI can provide images at the diffraction limit resolution that is only determined by the wavelength of radiation source and the effective numerical aperture of the recorded data. Since CDI has no need for high quality imaging optics, it is suitable for short wavelength radiations such as deep ultraviolet, X-rays, and electron beam, for which imaging optics of high performance are difficult to make. Meanwhile, the past 20 years have seen rapid progress of new type of light sources (cold emission electron guns, 3rd and 4th generation synchrotron X-rays sources, and free-electron lasers), array detectors with single particle sensitivity and broad dynamic range. All those progresses greatly promote the development of CDI. At present, CDI has shown some unique advantages over traditional methods in some study of materials science and biology, and gradually becomes a mainstream technology for certain applications. This paper briefly summarized the history of CDI with a focus on ptychography and coherent modulation imaging.
2019, 48(6): 603012.
doi: 10.3788/IRLA201948.0603012
Fourier ptychographic microscopy(FPM) is a promising label-free computational imaging technique with high resolution, wide field-of-view(FOV) and quantitative phase recovery. Due to its flexible setup, promising high-contrast performance without mechanical scanning and interferometric measurements, FPM has wide applications in the digital pathology, observation and dynamic imaging of label-free cells in vitro. In this review, the principle, research status and the latest advances were introduced in several aspects of FPM such as the system calibration methods, high-throughput imaging and high-speed imaging. The current problems and future trends were also presented.
2019, 48(6): 603013.
doi: 10.3788/IRLA201948.0603013
Three-dimensional(3D) imaging has attracted more and more interest because of its wide spread applications, especially in information and life science. These techniques can be broadly divided into two types:ray-based and wavefront-based 3D imaging. Issues such as imaging quality and system complexity of these techniques limit the applications significantly, and therefore many investigations are focused on 3D imaging from depth measurements. An overview of 3D imaging from depth measurements was presented, providing a summary of the connection between the ray-based and wavefront-based 3D imaging techniques, and showed the research direction of the depth measurement based 3D imaging research.
2019, 48(6): 603014.
doi: 10.3788/IRLA201948.0603014
Differential phase contrast(DPC) is a labeled-free and non-interferometric phase imaging method based on partial coherent illumination control, which provides a fast, effective and high-resolution visualization method for unstained transparent samples. It converts invisible sample phase information into detected intensity signals through multiple asymmetric illumination modulation or asymmetric aperture modulation, thereby providing possibilities for qualitative phase contrast imaging and even quantitative phase reconstruction samples. In recent years, with the gradual deepening of research in this field, the phase transfer function(PTF) of DPC imaging was definitely deduced, and DPC has gradually advanced towards qualitative observation to quantitative research. On the other hand, owning to the full-aperture illumination control and high-efficiency phase deconvolution algorithm,DPC quantitative phase imaging can achieve the incoherent diffraction limit resolution, and obtain a low-noise, high-precision quantitative phase reconstruction result. Furthermore, drawing on the theory of three-dimensional(3D) optical transfer function, DPC has recently been extended to 3D diffraction tomography to achieve quantitative imaging of the 3D refractive index for thick samples. This paper reviews the historical development, research status and latest developments from the basic principles of DPC imaging methods, imaging systems and algorithm optimization, and discusses some key problems existing in this method and possible future research directions.
2019, 48(6): 603015.
doi: 10.3788/IRLA201948.0603015
As an important means of image processing, the edge enhancement techniques play an important role in amplitude-contrast and phase-contrast objects imaging. The vortex filtering techniques based on radial Hilbert transform have attracted much attention because it can achieve isotropic edge enhancement. However, the classical vortex filtering causes background noise and contrast reduction due to diffraction caused by central singularities and sharp edges. In recent years, many research groups have proposed new types of vortex filters for vortex filtering side lobe suppression. In addition, the isotropic and anisotropic edge enhancement techniques based on vortex filtering have also developed rapidly. In this paper, several methods for suppressing vortex side lobes were summarized in recent years, including Laguerre Gaussian amplitude modulation, Bessel-like amplitude modulation, and Airy amplitude modulation. What's more, from two aspects:scalar vortex filtering and vector vortex filtering, the isotropic and anisotropic edge enhancement methods and progress were reviewed.
2019, 48(6): 603016.
doi: 10.3788/IRLA201948.0603016
In this paper, an optical scanning imaging system based on a single cylindrical lens rotation modulation was proposed. The complete wavefront information of the sample could be iteratively reconstructed by intensity patterns of the rotational modulation of the cylindrical lens. In addition, as a key parameter of the system, rotation angles of cylindrical lens were obtained by numerical calculation method based on the Radon transform, which got rid of the requirements for high-precision rotating equipment. Both the simulation and experimental results have verified the feasibility of the method. Compared with the axial multi-distance scanning imaging system, all optical components in the imaging system remain fixed in the axial position, so the data acquisition speed is accelerated and the axial sampling rate is kept fixed. It not only simplifies the algorithm design in the light field reconstruction, but also greatly speeds up the convergence speed.
2019, 48(6): 603017.
doi: 10.3788/IRLA201948.0603017
The compressive sensing reconstruction of magnified in-line hologram was experimentally researched in this paper. It aimed at the tomographic reconstruction of magnified multilayer samples. Firstly, the compressive sensing reconstruction of in-line hologram was introduced in theory, and the realization procedure was shown, including frequency domain down-sampling mode, the flow of two-step iterative algorithms, etc. Secondly, hologram recording system in case of point-source magnification and microscope objective magnification was established, the experimental work was carried out, which took multilayer samples as an example, and tomographic reconstruction of recorded in-line hologram based on compressive sensing. In the same time, it processed back-propagation reconstruction based on traditional convolution algorithm. The experimental results show that compressive sensing tomographic reconstruction technology can realize the tomographic reconstruction of holograms obtained in two magnification modes, and have better reconstruction results than the traditional convolutional inverse diffraction reconstruction. And it shows the ability and superiority of compressive-sensing tomographic reconstruction.
2019, 48(6): 603018.
doi: 10.3788/IRLA201948.0603018
Aiming at the non-interference phase retrieval technique based on Transport of Intensity Equation (TIE), which requires that the light source be monochromatic, and the mechanical error caused by moving CCD or object in the intensity acquisition process, a dispersion phase retrieval technique suitable for the lens model was proposed. The method was based on the phase transformation characteristic of the lens imaging system, and combined the dispersion with the TIE so that different wavelengths of light were imaged at the same position after passing through the lens system, thereby obtaining the focus and defocus intensity images without mechanical movement. Then, phase information of an object was calculated from the TIE by combining the relationship between the defocus amount and the wavelength. In this simulation, the correlation coefficient between the phase recovered by this method and the original phase is 0.970 7, and the RMSE is 0.061 8. At the same time, the phase of the lens array was restored by real experiment. The error between the experimental result and the real parameter is 1.74%, which proves the correctness and effectiveness of the proposed method.
2019, 48(6): 603019.
doi: 10.3788/IRLA201948.0603019
Multi-spectral video imaging can simultaneously collect spatial, temporal and spectral information of scenes. It can be widely used in many fields such as remote sensing, agricultural monitoring, material analysis, etc. However, traditional spectrometers often depend on optical dispersion spectroscopy structure, which makes the system complex and difficult to calibrate, and it is difficult to popularize. Therefore, a miniaturized multi-sensor spectral video imaging system was built in this paper. A fast alignment method of multi-view image or video based on camera poses was proposed to realize real-time acquisition and alignment of multi-spectral video on embedded system. Through the experimental verification of complex scenes, the alignment method proposed in this paper has achieved desired results in both objective index (e.g. PSNR, SSIM) and subjective visual effects.
