Scene-adaptive pattern coding-based fringe projection profilometry: diffuse surfaces identification and 3-D reconstruction in cluttered scenes.

Fringe projection profilometry (FPP) is one of the most widely used optical three-dimensional (3-D) perceiving techniques. However, when applied to cluttered scenes, acquiring accurate 3-D shapes is difficult because of the influences of indirect light caused by non-diffuse surfaces. In this paper, we first theoretically analyze and model the influences of indirect light in FPP, and then propose a scene-adaptive pattern coding-based method, which can design projection patterns based on the reflective properties of the scene's surfaces, to achieve accurate 3-D perceiving in cluttered scenes. Specifically, the scene confidence analysis method is first proposed to identify the reflective properties of various surfaces and localize the camera pixels of the diffuse surface. The illumination status (i.e., "0" or "1") of each projector pixel can be determined according to the camera-projection coordinate mapping and spatial pattern coding, where only diffuse surfaces can be illuminated, thus fundamentally preventing the influences of indirect light from the point of view of the light source. The 3-D shapes of diffuse surfaces can be accurately reconstructed in cluttered scenes. Different from traditional reflective properties change or light separation solutions, the proposed method can achieve accurate 3-D perceiving of cluttered scenes without additional hardware or expensive calculation. Extensive experiments verify that the proposed method outperforms the traditional methods in terms of accuracy and robustness.

Structured light 3-D sensing for scenes with discontinuous reflectivity: error removal based on scene reconstruction and normalization.

Structured light-based 3-D sensing technique reconstructs the 3-D shape from the disparity given by pixel correspondence of two sensors. However, for scene surface containing discontinuous reflectivity (DR), the captured intensity deviates from its actual value caused by the non-ideal camera point spread function (PSF), thus generating 3-D measurement error. First, we construct the error model of fringe projection profilometry (FPP). From which, we conclude that the DR error of FPP is related to both the camera PSF and the scene reflectivity. The DR error of FPP is hard to be alleviated because of unknown scene reflectivity. Second, we introduce single-pixel imaging (SI) to reconstruct the scene reflectivity and normalize the scene with scene reflectivity "captured" by the projector. From the normalized scene reflectivity, pixel correspondence with error opposite to the original reflectivity is calculated for the DR error removal. Third, we propose an accurate 3-D reconstruction method under discontinuous reflectivity. In this method, pixel correspondence is first established by using FPP, and then refined by using SI with reflectivity normalization. Both the analysis and the measurement accuracy are verified under scenes with different reflectivity distributions in the experiments. As a result, the DR error is effectively alleviated while taking an acceptable measurement time.

FPP-SLAM: indoor simultaneous localization and mapping based on fringe projection profilometry.

Simultaneous localization and mapping (SLAM) plays an important role in autonomous driving, indoor robotics and AR/VR. Outdoor SLAM has been widely used with the assistance of LiDAR and Global Navigation Satellite System (GNSS). However, for indoor applications, the commonly used LiDAR sensor does not satisfy the accuracy requirement and the GNSS signals are blocked. Thus, an accurate and reliable 3D sensor and suited SLAM algorithms are required for indoor SLAM. One of the most promising 3D perceiving techniques, fringe projection profilometry (FPP), shows great potential but does not prevail in indoor SLAM. In this paper, we first introduce FPP to indoor SLAM, and accordingly propose suited SLAM algorithms, thus enabling a new FPP-SLAM. The proposed FPP-SLAM can achieve millimeter-level and real-time mapping and localization without any expensive equipment assistance. The performance is evaluated in both simulated controlled and real room-sized scenes. The experimental results demonstrate that our method outperforms other state-of-the-art methods in terms of efficiency and accuracy. We believe this method paves the way for FPP in indoor SLAM applications.

Safety evaluation and pharmacodynamics of minocycline hydrochloride eye drops.

PURPOSE: This study evaluated the safe dosage of minocycline hydrochloride (Mino) eye drops and investigated the potential for the prevention or reduction of retinal damage in a diabetic rat model. METHODS: Various concentrations of Mino were applied to human corneal epithelial cells (HCECs) to determine the half maximal inhibitory concentration (IC50). The safety of Mino eye drops was evaluated on Sprague-Dawley (SD) rat eyes by slit-lamp examination, electroretinography (ERG), histology, and TUNEL assay. Eye drops (1 mg/ml) were applied to the streptozotocin-induced diabetic SD rats. Clinical observations, ERG analyses, and optical coherence tomography analyses were performed monthly for five months. Eyes were then analyzed via histology, blood-retinal barrier function assay, and retinal vascular staining. RESULTS: Cytotoxicity analysis using HCECs revealed that the IC50 was 250 µg/ml. Safety analyses in healthy SD rats showed that Mino eye drops did not demonstrate any ocular toxicity. Pharmacodynamics analysis showed that retinal thickness at three months was greater in the Mino group than in the non treated (NT) group. The peak times and amplitudes of each program were better in the Mino group than in the NT group at each time point by ERG analyses. Histology examinations showed a thinner ganglion cell layer, fewer ganglion cells, and more dilated blood vessels in the NT group than in the Mino group. CONCLUSION: Mino eye drops at 1 mg/ml were safe when used in SD rats. Mino eye drops can protect the retina from the development or progression of diabetic retinopathy.

Intravitreally Injected Methylene Blue Protects Retina against Acute Ocular Hypertension in Rats.

PURPOSE: To assess the neuroprotective effects of methylene blue (MB) in a rat model of acute ocular hypertension (AOH) and explore its possible mechanisms. METHODS: Our AOH rat model was obtained with anterior chamber perfusion for 60 min. After that, 100 µM MB was injected into the vitreous cavity immediately after injury. Electroretinogram, fundus photography, optical coherence tomography (OCT) and retina morphology examination were utilized to quantify retinal damage before surgery, as well as 7, 14 and 28 days after. The average number of surviving retinal ganglion cells (RGCs) was counted after fluorescent retrograde labelling with 4% DiI. And TUNEL assay was used to investigate retinal cell apoptosis at 24 hours after AOH. Nrf2 and BACE1 in the retina were determined by RT-qPCR analysis. RESULTS: AOH did produce a severe degeneration effect on the whole retinal layer. Intravitreally injected MB maintained certain retinal thickness after AOH, reduced the destruction of electroretinograms, and enhanced RGCs survival. The average number of TUNEL-labelled cells statistically reduced in the MB-treated retina tissue compared with retina treated with normal saline. The relative mRNA level of Nrf2 was also much higher in the MB-treated retinas after AOH, and the expression of BACE1 had a decline in the AOH + MB group. CONCLUSIONS: MB can protect the retina from AOH injury and the possible mechanism might involve the inhibition of BACE1 expression and the activation of Nrf2 antioxidant pathway.

De-noising imaging through diffusers with autocorrelation.

Recovering targets through diffusers is an important topic as well as a general problem in optical imaging. The difficulty of recovering is increased due to the noise interference caused by an imperfect imaging environment. Existing approaches generally require a high-signal-to-noise-ratio (SNR) speckle pattern to recover the target, but still have limitations in de-noising or generalizability. Here, featuring information of high-SNR autocorrelation as a physical constraint, we propose a two-stage (de-noising and reconstructing) method to improve robustness based on data driving. Specifically, a two-stage convolutional neural network (CNN) called autocorrelation reconstruction (ACR) CNN is designed to de-noise and reconstruct targets from low-SNR speckle patterns. We experimentally demonstrate the robustness through various diffusers with different levels of noise, from simulative Gaussian noise to the detector and photon noise captured by the actual optical system. The de-noising stage improves the peak SNR from 20 to 38 dB in the system data, and the reconstructing stage, compared with the unconstrained method, successfully recovers targets hidden in unknown diffusers with the detector and photon noise. With the help of the physical constraint to optimize the learning process, our two-stage method is realized to improve generalizability and has potential in various fields such as imaging in low illumination.

Neuroprotective effect of minocycline on rat retinal ischemia-reperfusion injury.

Purpose: To examine the neuroprotective effect of minocycline on retinal ischemia-reperfusion (IR) injury in rats and investigate its possible mechanism of action. Methods: Retinal IR injury was established by increasing the intraocular pressure in rats up to 110 mmHg for 60 min. The animals with retinal IR injury were intraperitoneally injected with 22.5 mg/kg minocycline twice a day for 14 days. The control group received the same amount of saline. Subsequently, funduscopic examination, retinal thickness measurement, retinal microvascular morphology, full-field electroretinography (ERG), retinal apoptotic cell count, and remaining retinal ganglion cell (RGC) count were performed. The expression of iNOS, Bax, Bcl2, IL-1α, IL-6, TNF-α, caspase-3, GFAP, Iba-1, Hif-1α, and Nrf2 was examined with real-time PCR and western blotting. Results: Minocycline treatment prevented IR-induced rat retinal edema and retinal cells apoptosis at the early stage and alleviated retina atrophy, blood vessel tortuosity, functional photoreceptor damage, and RGC degeneration at the late stage of the IR injury. At the molecular level, minocycline affected retinal gene and protein expression induced by IR. Conclusions: The results suggested that minocycline has a neuroprotective effect on rat retinal IR injury, possibly through anti-inflammation, antiapoptosis, antioxidation, and inhibition of microglial activation.

Locating and Imaging through Scattering Medium in a Large Depth.

Scattering medium brings great difficulties to locate and reconstruct objects especially when the objects are distributed in different positions. In this paper, a novel physics and learning-heuristic method is presented to locate and image the object through a strong scattering medium. A novel physics-informed framework, named DINet, is constructed to predict the depth and the image of the hidden object from the captured speckle pattern. With the phase-space constraint and the efficient network structure, the proposed method enables to locate the object with a depth mean error less than 0.05 mm, and image the object with an average peak signal-to-noise ratio (PSNR) above 24 dB, ranging from 350 mm to 1150 mm. The constructed DINet firstly solves the problem of quantitative locating and imaging via a single speckle pattern in a large depth. Comparing with the traditional methods, it paves the way to the practical applications requiring multi-physics through scattering media.

Spatial pattern-shifting method for complete two-wavelength fringe projection profilometry: erratum.

We present an erratum and generalization to our Letter [Opt. Lett.45, 3115 (2020)OPLEDP0146-959210.1364/OL.392102]. This erratum corrects an error in Eq. (12), and the generalization converts Rh to kh for more general situations of wavelengths. Neither has any influence on the conclusions of the original Letter.

Deep learning-based fringe modulation-enhancing method for accurate fringe projection profilometry.

Fringe projection profilometry (i.e., FPP) has been one of the most popular 3-D measurement techniques. The phase error due to system random noise becomes non-ignorable when fringes captured by a camera have a low fringe modulation, which are inevitable for objects' surface with un-uniform reflectivity. The phase calculated from these low-modulation fringes may have a non-ignorable phase error and generate 3-D measurement error. Traditional methods reduce the phase error with losing details of 3-D shapes or sacrificing the measurement speed. In this paper, a deep learning-based fringe modulation-enhancing method (i.e., FMEM) is proposed, that transforms two low-modulation fringes with different phase shifts into a set of three phase-shifted high-modulation fringes. FMEM enables to calculate the desired phase from the transformed set of high-modulation fringes, and result in accurate 3-D FPP without sacrificing the speed. Experimental analysis verifies its effectiveness and accurateness.

Spatial pattern-shifting method for complete two-wavelength fringe projection profilometry.

Two-wavelength fringe projection profilometry (FPP) unwraps a phase with the unambiguous phase range (UPR) of the least common multiple (LCM) of the two wavelengths. It is accurate, convenient, and robust, and thus plays an important role in shape measurement. However, when two non-coprime wavelengths are used, only a small UPR can be generated, and the unwrapping performance is compromised. In this Letter, a spatial pattern-shifting method (SPSM) is proposed to generate the maximum UPR (i.e., the product of the two wavelengths) from two non-coprime wavelengths. For the first time, to the best of our knowledge, the SPSM breaks the constraint of wavelength selection and enables a complete (i.e., either coprime or non-coprime) two-wavelength FPP. The SPSM, on the other hand, only requires spatially shift of the low-frequency pattern with the designed amounts and accordingly adjusting the fringe order determination, which is extremely convenient in implementation. Both numerical and experimental analyses verify its flexibility and correctness.

Dynamic 3-D measurement based on fringe-to-fringe transformation using deep learning.

Fringe projection profilometry (FPP) has become increasingly important in dynamic 3-D shape measurement. In FPP, it is necessary to retrieve the phase of the measured object before shape profiling. However, traditional phase retrieval techniques often require a large number of fringes, which may generate motion-induced error for dynamic objects. In this paper, a novel phase retrieval technique based on deep learning is proposed, which uses an end-to-end deep convolution neural network to transform a single or two fringes into the phase retrieval required fringes. When the object's surface is located in a restricted depth, the presented network only requires a single fringe as the input, which otherwise requires two fringes in an unrestricted depth. The proposed phase retrieval technique is first theoretically analyzed, and then numerically and experimentally verified on its applicability for dynamic 3-D measurement.

Synthesis of Fe-Fe3O4/rGO Composite with Heterostructure Through Room-Temperature Reduction as Photo-Fenton Catalyst.

A Fe-Fe3O4/rGO nanocomposite with heterostructure has been successfully synthesized by a highyield, low-cost, and easily operated room-temperature reduction method. The novel Fe-Fe3O4/rGO composite exhibits an excellent activity for the degradation of Orange II under visible light by the Photo-Fenton process, which is 92.06% after 180 minutes. Moreover, magnetic analysis indicated that the prepared Fe-Fe3O4/rGO composite possesses ferromagnetic properties, which enable it to be magnetically separated for recycling purposes.

Highly sensitive and selective electrochemical immunosensors by substrate-enhanced electroless deposition of metal nanoparticles onto three-dimensional graphene@Ni foams.

In this study, we have for the first time preformed the facile substrate-enhanced electroless deposition (SEED) of metal nanoparticles onto monolithic graphene@Ni foams for construction of disposable three-dimensional (3D) electrochemical immunosensors. Specifically, we firstly used the SEED method to deposit gold nanoparticles (AuNPs) onto the graphene@Ni foam for immobilization of antibody (Ab1). This is followed by a second step SEED deposition to produce silver nanoparticles (AgNPs) for electrochemical stripping detection. Using α-fetoprotein antigen (AFP) as a module analyte, the newly-developed sensor showed a wide linear response, ranging from 5.0 pg/mL to 5.0 ng/mL and a low detection limit down to 2.3 pg/mL. The newly-developed 3D-immunosensor is sensitive, reliable, and easy to be fabricated, showing great potential for clinic applications.

Ternary Gray code-based phase unwrapping for 3D measurement using binary patterns with projector defocusing.

The three-dimensional measurement technique using binary pattern projection with projector defocusing has become increasingly important due to its high speed and high accuracy. To obtain even faster speed without sacrificing accuracy, a ternary Gray code-based phase-unwrapping method is proposed by using even fewer binary patterns, which makes it possible to efficiently and accurately unwrap the phase. Theoretical analysis, simulations, and experiments are presented to validate the proposed method's efficiency and robustness.

Phase-shifting profilometry combined with Gray-code patterns projection: unwrapping error removal by an adaptive median filter.

Phase-shifting profilometry combined with Gray-code patterns projection has been widely used for 3D measurement. In this technique, a phase-shifting algorithm is used to calculate the wrapped phase, and a set of Gray-code binary patterns is used to determine the unwrapped phase. In the real measurement, the captured Gray-code patterns are no longer binary, resulting in phase unwrapping errors at a large number of erroneous pixels. Although this problem has been attended and well resolved by a few methods, it remains challenging when a measured object has step-heights and the captured patterns contain invalid pixels. To effectively remove unwrapping errors and simultaneously preserve step-heights, in this paper, an effective method using an adaptive median filter is proposed. Both simulations and experiments can demonstrate its effectiveness.

Phase error analysis and compensation for phase shifting profilometry with projector defocusing.

Phase shifting profilometry (PSP) using binary fringe patterns with projector defocusing is promising for high-speed 3D shape measurement. To obtain a high-quality phase, the projector usually requires a high defocusing level, which leads to a drastic fall in fringe contrast. Due to its convenience and high speed, PSP using squared binary patterns with small phase shifting algorithms and slight defocusing is highly desirable. In this paper, the phase accuracies of the classical phase shifting algorithms are analyzed theoretically, and then compared using both simulation and experiment. We also adapt two algorithms for PSP using squared binary patterns, which include a Hilbert three-step PSP and a double three-step PSP. Both algorithms can increase phase accuracy, with the latter featuring additional invalid point detection. The adapted algorithms are also compared with the classical algorithms. Based on our analysis and comparison results, proper algorithm selection can be easily made according to the practical requirement.

Phase coding method for absolute phase retrieval with a large number of codewords.

A recently proposed phase coding method for absolute phase retrieval performs well because its codeword is embedded into phase domain rather than intensity. Then, the codeword can determine the fringe order for the phase unwrapping. However, for absolute phase retrieval with a large number of codewords, the traditional phase coding method becomes not so reliable. In this paper, we present a novel phase coding method to tackle this problem. Six additional fringe images can generate more than 64(2(6)) unique codewords for correct absolute phase retrieval. The novel phase coding method can be used for absolute phase retrieval with high frequency. Experiment results demonstrate the proposed method is effective.