Focus Detection Method Research Articles

Preference Learning to Multifocus Image Fusion via Generative Adversarial Network

Multifocus image fusion (MFIF) is to produce an all-in-focus fused image by integrating a pair of multifocus images with the same scene. In this article, an effective focus detection method is proposed for MFIF, by a generative adversarial network (GAN) with preference learning (PL). Benefitting from more obvious focus characteristics from the luminance channel in HSV, we take this luminance as the input of our GAN to carry out the easier focus detection, instead of the grayscale images in existing methods. On the other hand, to train our GAN more effectively, we utilize the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\ell }_{{2},{1}}$ </tex-math></inline-formula> norm to construct a focus fidelity loss with structural group sparseness, to regularize the generator loss, pledging a more accurate focus confidence map. More importantly, a novel learning strategy, termed PL, is further developed to enhance model training. Functionally, it assigns a larger learning weight to a sample more difficult to be learned. Extensive experiments demonstrate that our proposed method is superior to other state-of-the-art methods.

Large-range and high-precision autofocus method based on an annular DOE for a laser direct writing system.

We present a large-range and high-precision autofocus method based on an annular diffractive optical element (DOE) for a laser direct writing system. By analyzing the shape of the return spot, the defocus direction and the defocus amount can be obtained at the same time. The experimental results show that the linear detection range of the proposed method can reach at least 76 µm, the sensitivity can reach 100 nm, the detection accuracy can reach 100 nm, and the noise fluctuation does not exceed 50 nm. Apparently, with the advantages of a large detection range, high detection, and good stability, the automatic focus detection method proposed in this paper can be widely applied in various wafer-scale complex microstructure preparation systems.

A Multifocus Image Fusion Scheme Based on Similarity Measure of Transformed Isosceles Triangles Between Intuitionistic Fuzzy Sets

Intuitionistic fuzzy set (IFS) theory is widely used to solve imprecise and uncertain problems, and the similarity measure between IFSs can describe the similarity or dissimilarity degree of objects in the real word. In image fusion, it is a key issue to measure and extract the features of multifocus images to fuse them. This research proposes a similarity measure technique of IFSs, which is introduced into image fusion to measure the feature similarity of adjacent pixels. In this work, we present an available similarity measure method between IFSs and propose an image fusion method based on this measure and also design an edge reserved method based on the Canny edge detection to reinforce the image fusion effect. First, the proposed similarity measure is introduced and proved. Second, a focus detection method that can detect the focused regions of an image is designed based on the proposed measure method of IFSs to obtain a preliminary decision map. Third, morphological operations are employed to generate the secondary decision map. Fourth, a Canny edge model-based technique is designed to preserve the edges of the source images. Extensive experiments show that the presented similarity measure method of IFSs is reliable, and the fuzzy measure-based image fusion scheme is effective compared with current methods.

Machine vision-based high-precision and robust focus detection for femtosecond laser machining

We propose a machine vision-based focus detection method (MVFD) for femtosecond laser machining. By analyzing the laser focus pattern, the defocus direction and distance are obtained simultaneously. The proposed technique presents high precision with an average error of 0.047 µm and a root mean square error (RMSE) of 0.055 µm. Moreover, the method is robust and is less affected by the tilted sample. For the curved surface sample, the average error and RMSE are 0.093 and 0.145 µm, respectively. Thus, the proposed focus detection method can be easily combined with laser processing equipment, which is widely used in large-range and high-precision femtosecond laser processing.

Multi-focus image fusion algorithm based on focus detection in spatial and NSCT domain.

Multi-focus image fusion is an effective approach to obtain the all-in-focus image. Focus detection is the key issue of multi-focus image fusion. Aiming at the shortcoming of spatial domain and transform domain algorithms for multi-focus image fusion, a novel multi-focus image fusion algorithm is proposed by combing focus detection in spatial domain and non-subsampled contourlet transform (NSCT) domain. At first, the focused pixels are detected by the sum-modified-Laplacian algorithm in spatial domain. At the same time, the focus detection method is proposed in NSCT domain, namely by MPCNN and voting fusion methods for high-frequency subbands of NSCT. Then, the morphological operation is utilized to correct the focus detection results in spatial domain and NSCT domain. At last, synthesis of detection results is implemented and the fused image can be obtained. Experimental results verified that the proposed algorithm outperformed some state-of-the-art fusion algorithms in terms of both subjective observation and objective evaluations.

A Non-Contact Displacement Sensor with Diffraction Grating Metrology System for Profile Measurement

Focus detection method is one of non-contact profile measurement methods. However, the measurement accuracy of current focus detection method is limited by voice coil motor adopted by it. In this paper, based on an improved Foucault focus detection method, a new non-contact displacement sensor with diffraction grating metrology system is presented. Driven by a piezoelectric actuator instead of a voice coil motor, and a diffraction grating metrology system being with it, the sensor has high measurement accuracy. During surface profile sampling, according to focusing deviation signal, the focusing lens was driven to move vertically by the piezoelectric actuator so that its focus was always located on the workpiece surface, synchronously the vertical displacement of the focusing lens was obtained by the diffraction grating metrology system as the profile height of sampling points. The displacements of all sampling points gave the whole profile of the measured surface, which can be processed by a characterization software to obtain the measurement result. The resolution of the non-contact displacement sensor was 10 nm.

Investigation of potential zooanthroponotic transmission of cryptosporidiosis and giardiasis through agricultural use of reclaimed wastewater*

A field study in the Juarez Valley of Mexico was performed to investigate the potential transmission of Cryptosporidium and Giardia to sheep livestock grazing on forage irrigated with reclaimed wastewater, and the potential for disease transmission back to humans. United States Environmental Protection Agency Method 1623 immunofluorescent assay (IFA) revealed high levels of pathogens in reclaimed wastewater, with 183 to >7000 Giardia cysts and 9 – 762 Cryptosporidium oocysts detected per litre. Infectious Cryptosporidium were detected in the reclaimed wastewater using the cell culture focus detection method (FDM). Polymerase chain reaction (PCR) analyses revealed reclaimed wastewater contained the C. parvum bovine (zoonotic) genotype, human-specific C. hominis subgenotypes, and G. lamblia (syn. G. duodenalis, G. intestinalis) Assemblage A genotypes (A2 and A3). Despite high levels of Cryptosporidium and Giardia in the reclaimed wastewater, these pathogens were rarely found on the forage plants, possibly due to environmental attenuation. Sheep fecal specimens were positive for only livestock-associated G. lamblia Assemblage E genotypes. Therefore, in this field study, there was no evidence of zooanthroponotic transmission of Cryptosporidium or Giardia.

Assessment of methods for detection of infectious Cryptosporidium oocysts and Giardia cysts in reclaimed effluents.

This study evaluates the occurrence of Cryptosporidium oocysts and Giardia cysts in reclaimed effluents if method 1623 with the Envirochek capsule filters (standard and high-volume [HV] filters) and a modified version of the Information Collection Rule method (ICR) with the polypropylene yarn-wound cartridge filter are used. The recovery efficiency of the analytical methods was evaluated with samples of reagent, tap, and reclaimed water by using flow cytometer-sorted spike suspensions. (Oo)cyst recovery efficiency determined filter performance and method reproducibility in the water matrix tested. Method 1623 with the Envirochek HV capsule filter generated significantly higher recovery rates than did the standard Envirochek filter and the modified ICR method. Notwithstanding, large variations in recovery rates (>80%) occurred with samples of reclaimed water, and none of the water quality parameters analyzed in the reclaimed effluents could explain such variability. The highest concentrations of indigenous oocysts were detected by method 1623 with the HV filter, which provided a sufficient number of oocysts for further confirmation of infectious potential. Confirmation of species and potential infectivity for all positive protozoan samples was made by using a nested PCR restriction fragment polymorphism assay and the focus detection method most-probable-number assay, respectively. The methodology and results described in the present investigation provide useful information for the establishment of pathogen numeric standards for reclaimed effluents used for unrestricted irrigation.

Improving the rate of infectivity of Cryptosporidium parvum oocysts in cell culture using centrifugation.

Centrifugation was evaluated as a method to improve infectivity assays of Cryptosporidium parvum in cell culture using the focus detection method, an immunofluorescence-based method for detecting infectious C. parvum oocysts in vitro. Human ileocecal adenocarcinoma (HCT-8) cells were grown for 48 hr on 13-mm cover slips in 24-well microtiter plates and infected with bleach-treated C. parvum oocysts. Plates were centrifuged at 228 g for 10 min and incubated at 37 C for 5, 12, 18, 24, and 48 hr. Foci of infection were stained by immunofluorescence and enumerated using epifluorescent microscopy. Results were compared to noncentrifuged controls. Foci in centrifuged samples could be enumerated after 18 hr. According to most probable number (MPN) analysis, the number of infectious oocysts estimated at 48 hr (13,326 infectious oocysts) was reached by 18 hr in centrifuged samples. After 48 hr, there was no significant difference (P < 0.05) between centrifuged and noncentrifuged samples enumerated by number of foci or the MPN of infectious oocysts. Centrifugation may expedite detection during C. parvum infectivity assays. Furthermore, multiwell plate formats are more cost effective than traditional chamber slides.

A most-probable-number assay for enumeration of infectious Cryptosporidium parvum oocysts.

Cryptosporidium is globally established as a contaminant of drinking and recreational waters. A previously described cell culture infectivity assay capable of detecting infectious oocysts was adapted to quantify viable oocysts through sporozoite invasion and clustering of foci. Eight experiments were performed by using oocysts less than 4 months of age to inoculate host HCT-8 cell monolayers. Oocysts were diluted in a standard 5- or 10-fold multiple dilution format, levels of infection and clustering were determined, and the most probable number (MPN) of infectious oocysts in the stock suspension was calculated. The MPN was compared to the initial oocyst inoculum to determine the level of correlation. For oocysts less than 30 days of age, the correlation coefficient (r) was 0.9726 (0.9306 to 0.9893; n = 20). A two-tailed P value (alpha = 0.05) indicated that P was less than 0.0001. This strong correlation suggests that the MPN can be used to effectively enumerate infectious oocysts in a cell culture system. Age affected the degree of oocyst infectivity. Oocyst infectivity was tested by the focus detection method (FDM)-MPN assay and in BALB/c mice before and after treatment with pulsed white light (PureBrite). The FDM-MPN assay and animal infectivity assays both demonstrated more than a 4 log(10) inactivation. Municipal water systems and a host of other water testing organizations could utilize the FDM-MPN assay for routine survival and disinfection studies.

Holographic Optical Element with High Assembly Tolerance for the Optical Module of Digital Versatile Disc Pickup-Heads

The astigmatic focus detection method and differential phase detection (DPD) tracking method are now widely used in a digital versatile disk (DVD) pickup head. The DPD tracking method requires the returning spot to remain centered in a quad detector and therefore makes the optical alignment very critical. In this paper, a novel holographic optical element (HOE) pattern design to relax the alignment tolerance and achieve a stable DPD tracking servo property is described. Simulations show that the servo signals are insensitive to photo-detector (PD) misalignment when compared to that of a conventional HOE design.

Robust Focus and Tracking Detection for Holographic Digital Versatile Disc Optical Pickup-Head Modules

This paper introduces a robust focus and tracking detection method for use in holographic pickup heads. The method, which we call split-aperture servo detection, provides the focus error signal and both differential phase detection (DPD) and pushpull tracking signals but requires one less axis of alignment than the commonly used quad detector with astigmatic focus detection. A set of simulations designed according to Taguchi's method is presented comparing the manufacturability of holographic modules using the split-aperture approach and the astigmatic approach. The split-aperture approach is seen to have strong advantages. Experimental verification of a prototype digital versatile disc (DVD) pickup is also presented.

An in vitro method for detecting infectious Cryptosporidium oocysts with cell culture.

Current assay methods to detect Cryptosporidium oocysts in water are generally not able to evaluate viability or infectivity. A method was developed for low-level detection of infective oocysts by using HCT-8 cells in culture as hosts to C. parvum reproductive stages. The infective foci were detected by labeling intracellular developmental stages of the parasite in an indirect-antibody assay with a primary antibody specific for reproductive stages and a secondary fluorescein isothiocyanate-conjugated antibody. The complete assay was named the focus detection method (FDM). The infectious foci (indicating that at least one of the four sporozoites released from a viable oocyst had infected a cell) were enumerated by epifluorescence microscopy and confirmed under Nomarski differential interference contrast microscopy. Time series experiments demonstrated that the autoreinfective life cycle in host HCT-8 cells began after 12 h of incubation. Through dilution studies, levels as low as one infectious oocyst were detected. The cell culture FDM compared well to other viability assays. Vital stains and excystation demonstrated that oocyst populations less than 1% viable (by vital dyes) and having a low sporozoite yield following excystation could not infect host cells. Until now, the water industry has relied on an oocyst detection method (under an information collection regulation) that is unable to determine viability. The quantifiable results of the cell culture method described demonstrate two important applications: (i) an infectivity assay that may be used in conjunction with current U.S. Environmental Protection Agency-mandated detection methodologies, and (ii) a method to evaluate oocyst infectivity in survival and disinfection studies.

Focus detection method utilizing surface acoustic wave

Method for detecting a focus condition of an imaging optical system by using a surface acoustic wave device is disclosed. A light receiving element array formed by a plurality of light receiving elements receives a light flux transmitted through at least a part of an image formed by the imaging optical system. Then, outputs of said light receiving elements are processed on real time by means of a Fourier transform device including a surface acoustic wave device, a convolver, etc. so as to derive an image sharpness and/or an image lateral shift, both of which are used for a focus detection. Therefore, as compared with a conventional focus detection method, it is possible to perform the focus detection in a fast and accurate manner by a simple and small construction.