Weld quality inspection allows the detection of defects that may compromise the quality and strength of the weld. Although visual optical inspection offers lower reliability than other non-destructive methods, it enables weld analysis at a significantly lower cost. In this context, developing machine learning-based algorithms for automatic optical weld quality recognition requires acquiring large amounts of data for training. This entails high costs in terms of time, material and energy required for test preparation. However, one possible approach to tackling the problem with limited datasets is to use synthetic data. Using such data increases the amount and variety of data available to the detection algorithm. With a focus on the context of welding, this paper presents an approach that uses synthetic data as a form of data augmentation to improve the performance of the optical detection of weld seams. Specifically, we propose a generative neural network for semantic image synthesis using a limited starting dataset. The network generates new data instances by receiving as input a semantic map of the image to be represented. Weld defects such as porosity or weld spatter are added to the semantic map so that the network synthesizes corresponding defect images. Analysing the performance on a segmentation network, experimental results show how adding synthetic data to the original data can ensure improvements in network performance.
Achieving clear vision through smoke and flames is a highly pursued goal to better manage intervention priorities and to allow first responders operating safely during fire accidents. Here we show active far-infrared systems to image static/moving targets through fire with different imaging performance and field-portability characteristics. Low-coherence infrared systems and high-coherence holographic sensors will be discussed. We show that a pre-trained convolutional neural network can detect the presence of a person hidden behind fire in real-time, accurately, even when the system is not able to reject the flame contributions in full, being suitable for video-surveillance applications.
Digital holography (DH) has been demonstrated as a very powerful tool for micro-plastics (MPs) imaging and recognition, thanks to its unique capabilities such as label-free 3D imaging, flexible focusing and high-throughput. Moreover, the use of machine learning approaches has permitted to surpass main processing limitations in classifying MPs. In particular, the quantitative phase signature provided by DH permits to identify the unique fingerprint for MPs that is crucial to improve the accuracy in features based classification task. In this paper, we investigate new optical, morphological and texture features that can be calculated from phase images of MPs only.
Diatoms are one of the largest groups of microalgae present in marine, freshwater and transitional environments and their reactivity to environmental changes makes them suitable to be employed as biomarkers for monitoring tasks. Anyway, their presence in a large number of species makes it arduous to perform diatoms taxonomy during monitoring tasks considering that, to date, analysis is conducted by marine biologists on the basis of their own experience and, hence, in a subjective way. Hence, the need for automatic and objective methodologies for the identification and classification of diatoms samples rises. Research efforts in the field of Computer Vision led to a plethora of highly effective deep learning strategies surpassing human capabilities for image classification, as showed in the recent Imagenet challenge editions where they were initially introduced. Despite the very promising results of the proposed solutions, the difficulty arises to determine which technique is most suitable among them for real tasks and in particular for diatoms classification. This work proposes an end-to-end pipeline for automatic recognition of diatoms, acquired by means of holographic microscopy in water samples, employing deep learning techniques. In particular the most recently introduced Convolution Neural Networks (CNNs) architectures have been deeply investigated and compared in order to highlight the pros and cons of each of them. Moreover, in order to feed the CNNs training stages with a suitable amount of labeled data, a strategy to build a synthetic dataset, starting from a single image per class available from commercial glass slides specifically prepared for taxonomy purposes, is introduced. Besides, models ensembling strategies, in order to improve the single model scores, have been exploited. Finally, the proposed approach has been validated employing a dataset built up of holographic images of diatoms sampled in natural water bodies.
Microplastics are worrisome water pollutants that are more and more spread in deep sea and coastal waters. Plastic items can take decades to biodegrade, have the potential to affect the food chain and are harmful to marine life. Hence, there is the urgent need to define protocols and to create reliable tools to map the presence of microplastics in heterogeneous liquid samples. However, well established protocols and tools to identify microplastics in water have not been proposed yet. Here we investigate this class of objects by means of coherent imaging, in particular relying on Digital Holography (DH) microscopy. We provide a DH characterization of the “plastic” class that can be used as a global identifier independently on the plastic material under analysis. We probe microplastics of various materials through our DH microscope and show that the phase contrast map of microplastics can be used to define a fingerprint for the microplastics population. Thanks to the DH flexible refocusing, volumetric counting of microplastics in flow is feasible by DH with high-throughput. Remarkably, field-deployable, cost effective DH microscopes exist that can bring the DH characterization potential out of the lab for in situ environmental monitoring.
Learning to automatically recognize objects in the real world is a very important and stimulating challenge. This work deals with the problem of detecting aluminium profiles within images, using hierarchical representations such as those based on deep learning methods. The use of regional CNN, a conceptually simple, flexible, and general framework for object instance segmentation, allows to exceed the previous state-of-the-art results. This approach efficiently detects objects in an image while simultaneously generating a high-quality segmentation mask for each instance. Neural network training uses ResNet networks of depth 50 or 101 layers. In particular, the training dataset consists of synthetic data generated by CAD files. The Dataset creation process is fundamental: experimental results show that trivial datasets lead to poor detection performance. A rich dataset, instead, including more complex images, allows the network to learn more and better guaranteeing excellent results. How to get more data, if you do not have more data? To get more data, we just need to make minor alterations such as flips, scale or rotations to existing dataset. This process is known as Data augmentation. The performance of the proposed system strongly depends on the dataset used for training and on the backbone architecture used. This why, adopting a strategy that generates a priori a very large dataset the time required to create the annotation file grows almost exponentially. The validation and test dataset, on the other hand, consists of real images captured by cameras. The distinctiveness of this work consists to train a deep neural network with synthetic data (aluminium CAD files) and verify if it on real data. Experiments show that the implementation of architecture, as described above, leads to good performance in automatic detection and classification. Future work will be addressed to improve the network training process together with the architecture, the algorithms and the dataset creation process. The latter is proved to be fundamental for the balance and optimization of the whole process. The way is to develop not much augmented datasets focusing on online data augmentation during network training.
In sheet metal production the quality of a cut determines the conditions for a possible postprocessing. Considering the roughness as a parameter for assessing the quality of the cut edge, different techniques have been developed that use texture analysis and convolutional neural networks. All methods available require the use of appropriate equipment and work only in fixed light conditions. In order to discover new applications in the contexts of Industry 4.0, there is a necessity to go beyond their intrinsic limits as camera types and light condition while ensuring the same level of performance. Taking into account the strong increase of the smartphones features in recent years and the fact that their performance in some respect is now comparable to that of a PC with a middle-range mirrorless camera, it is no longer utopian to think of a new out-of-the-box use of these devices that employs the capability in a new way and in a new context. Therefore, we present a method that uses a mobile device with a camera to guarantee images of sufficient quality that can be used for further processing in order to determine the quality of the metal sheet edge. After the image acquisition of the sheet metal edge in real condition of use, the method uses a trained deep neural network to identify the sheet metal edge present in the picture. After the segmentation a no-reference image quality algorithm provides an image quality index, in terms of blurriness, for the image region of the cut edge. This way it is possible for the further evaluation of the cut edge to only consider image data that satisfies a specific quality, ignoring all the parts of the picture with a bad image quality.
The identification and classification of biological samples is high-demanded in biomedical imaging for diagnostic purposes. Among all imaging modalities, digital holography has gained credits as a powerful solutions, thanks to its ability to perform full-field and label –free quantitative phase imaging. On the other hand, machine learning is nowadays the most used approach for classification purposes. The robustness and the accuracy of the classification depend of the features used for the training step. Therefore, the identification of micro-organism becomes strictly related to the features that can be extracted from their images. In other word, the more the image contains information, the higher the possibility of extracting highly distinctive descriptors to differentiate biological phenotypes. Digital holography can be considered one of the richest in terms of information content due to the fact that a single digital hologram encode both amplitude and phase information about the imaged cells. This opens the way to improve the features extraction, thus making more accurate the classification step. In this paper we analyze a test case by using a holographic image dataset for classification, by extracting unique features that can be solely obtained by holographic images.
Nowadays, digital holography can be considered as one of the most powerful imaging modality in several research fields, from the 3D imaging for display purposes to quantitative phase image in microscopy and microfluidics. At the same time, machine learning in imaging applications has been literally reborn to the point of being considered the most exploited field by optical imaging researchers. In fact, the use of deep convolutional neural networks has permitted to achieve impressive results in the classification of biological samples obtained by holographic imaging, as well as for solving inverse problems in holographic microscopy. Definitely, machine learning approaches in digital holography has been used mainly to improve the performance of the imaging tool. Here we show a reverse modality in which holographic imaging boosts the performance of machine leaning algorithms. In particular, we identify several descriptors solely related to the type of data to be classified, i.e. the holographic image. We provide some case studies which demonstrate how the holographic imaging can improve the performance of a plain classifier.
Micro-plastics dispersion in water is one of the major global threats due to the potential of plastic items to affect the food chain and reproduction of marine organisms. However, reliable and automatic recognition of micro-plastic in water is still an unmatched goal. Here we identify micro-plastics in water samples through digital holography microscopy combined to machine learning. We exploit the rich content of information of the holographic signature to design new distinctive features that specifically characterize micro-plastics and allow distinguishing them from marine plankton of comparable size. We use these features to train a plain support vector machine, remarkably improving its performance. Thus, we obtain a very accurate classifier using a simple machine learning approach, which does not require a large amount of training data and identifies micro-plastics of various morphology and optical properties over a wide range of characteristic scales. This is a first mandatory step to develop sensor networks to map the distribution of micro-plastics in water and their flows.
We propose a complete framework for the synthesis of 3D holographic scene, combining multiple color holograms of different objects by applying adaptive transformations. In particular, it has been demonstrated that affine transformation of digital holograms can be employed to defocus and chromatic aberrations. By combining these two features we are able to synthesize a color scene where multiple objects are jointly multiplexed. Since holograms transformation could be introduce artifacts in the holographic reconstructions, principally related to the presence of speckle noise, we also implement a denoising step where the Bi-dimensional Empirical Mode Decomposition (BEMD) algorithm is employed. We test the proposed framework in two different scenario, i.e. by coding color three-dimensional scenes and joining different objects that are (i) experimentally recorded and (ii) obtained as color computer generated holograms (CCGH).
In recent years, "FragTrack" has become one of the most cited real time algorithms for visual tracking of an object in a video sequence. However, this algorithm fails when the object model is not present in the image or it is completely occluded, and in long term video sequences. In these sequences, the target object appearance is considerably modified during the time and its comparison with the template established at the first frame is hard to compute. In this work we introduce improvements to the original FragTrack: the management of total object occlusions and the update of the object template. Basically, we use a voting map generated by a non-parametric kernel density estimation strategy that allows us to compute a probability distribution for the distances of the histograms between template and object patches. In order to automatically determine whether the target object is present or not in the current frame, an adaptive threshold is introduced. A Bayesian classifier establishes, frame by frame, the presence of template object in the current frame. The template is partially updated at every frame. We tested the algorithm on well-known benchmark sequences, in which the object is always present, and on video sequences showing total occlusion of the target object to demonstrate the effectiveness of the proposed method.
KEYWORDS: Speckle, Image filtering, Image processing, Digital filtering, Denoising, Image quality, Digital holography, Holograms, Signal processing, 3D image reconstruction
The paper presents a new automatic technique for speckle reduction in the context of digital holography. Speckle noise is a superposition of unwanted spots over objects of interest, due to the behavior of a coherence source of radiation with the object surface characteristics. In the proposed denoising method, bidimensional empirical mode decomposition is used to decompose the image signal, which is then filtered through the Frost filter. The proposed technique was preliminarily tested on the “Lena” image for quality assessment in terms of peak signal-to-noise ratio. Then, its denoising capability was assessed on different holographic images on which also the comparison (using both blind metrics and visual inspection) with the leading strategies in the state of the art was favorably performed.
A new method to automatically locate pupils in images (even with low resolution) containing near-frontal human faces is presented. In particular, pupils are localized by an unsupervised procedure consisting of two steps: at first, self-similarity information is extracted by considering the appearance variability of local regions, and then it is combined with an estimator of circular shapes based on a modified version of the circular Hough transform. Experimental evidence of the effectiveness of the method was achieved on challenging databases and video sequences containing facial images acquired under different lighting conditions and with different scales and poses.
We propose an algorithm for the automatic estimation of the in-focus image and the recovery of the correct reconstruction
distance for digital holograms. We tested the proposed approach applying it to stretched digital holograms. In fact, by
stretching an hologram with a variable elongation parameter, it is possible to change the in-focus distance of the
reconstructed image. In this way, the reliability of proposed algorithm can be verified at different distances dispensing with
the recording of different holograms. Experimental results are shown with the aim to demonstrate the usefulness of the
proposed method and a comparative analysis has been performed with respect to other algorithms developed for digital
holography.
Searching and recovering the correct reconstruction distance in digital holography can be a cumbersome and subjective
procedure. Here we show an algorithm for the automatically estimating the in-focus image and recovering the correct
reconstruction distance for speckle holograms. We have tested the approach in determining the reconstruction distances
of stretched digital holograms. Stretching a hologram with a variable elongation parameter gives us the possibility to
change the in-focus distance of the reconstructed image. In this way, the proposed algorithm can be verified at different
distances by dispensing the recording of different holograms. Experimental results are shown with the aim to
demonstrate the usefulness of the proposed method and a comparative analysis has been performed with respect to other
existing algorithms developed for digital holography.
We developed a novel method to detect the presence of unburned diesel fuel in used diesel fuel engine oil. The method is
based on the use of an array of different gas microsensors based on metal oxide thin films deposited by sol-gel technique
on Si substrates. The sensor array, exposed to the volatile chemical species of different diesel fuel engine oil samples
contaminated in different percentages by diesel fuel, resulted to be appreciable sensitive to them. Principal Component
Analysis (PCA) and Self-Organizing Map (SOM) applied to the sensor response data-set gave a first proof of the sensor
array ability to discriminate among the different diesel fuel diluted lubricating oils. Moreover, in order to get information
about the headspace composition of the diesel fuel-contaminated engine oils used for gas-sensing tests, we analyzed the
engine oil samples by Static Headspace Solid Phase Micro Extraction/Gas Chromatograph/Mass Spectrometer (SHS-SPME/
GC/MS).
In the last years the detection and classification of surface defects of material is assuming great importance. Visual inspection can help to increase the product quality and, in particular context, the maintenance of products. The railway infrastructure is a particular field in which the periodical surface inspection of rolling plane can help an operator to prevent critical situation. We use a Gabor filter to emphasize the image regions with grey level variation. The Gabor filter h(x,y) is characterized by a frequency F, direction (theta) and parameter (sigma) . We have selected experimentally four filters with directions 0, (pi) /4, (pi) /2 and (pi) 3/4 with F equals (root)2/8 cycle/pixel and (sigma) equals 2. The problem of detection and classification is a crucial part of our work because cannot be defined an exhaustive training set of defect and no-defect images. It is necessary a method able to self-learn changes. Investigating about this problem we propose in the paper a novel Self Organized Map (SOM) network, appropriately modified, for detection and classification of rail defects. The proposed SOM network learns to classify input vectors according to how they are grouped in the input space. So, SOM learns both the distribution and topology of the input vectors belonging to the training set. During the training phase, the neurons in the layer of an SOM form some cluster or bubble representing the input training with minimum distance among them. The novelty is to modify the SOM network in order to learn continuously during the test phase.
Developing elementary behavior is the starting point for the realization of complex systems. We present a learning algorithm that realizes a simple goal-reaching behavior for an autonomous vehicle when no a-priori knowledge of the environment is provided. Information coming from a visual sensor is used to detect a general state of the system. To each state an optimal action is associated using a Q- learning algorithm. As sets of states and actions are limited, a few training trials are sufficient in simulation to learn the optimal policy. During test trials (both in simulated and real environment) fuzzy sets with membership functions are introduced to compute the state of the system and the proper action at the extent of tackling errors in state estimation due to noise in vision measures. Experimental results both in simulated and real environment are shown.
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