Person: Pajares Martínsanz, Gonzalo
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First Name
Gonzalo
Last Name
Pajares Martínsanz
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Informática
Department
Ingeniería del Software e Inteligencia Artificial
Area
Lenguajes y Sistemas Informáticos
Identifiers
5 results
Search Results
Now showing 1 - 5 of 5
Item Layer factor analysis in convolutional neural networks for explainability(Applied Soft Computing, 2024) López González, Clara Isabel; Gómez Silva, María José; Besada Portas, Eva; Pajares Martínsanz, GonzaloExplanatory methods that focus on the analysis of the features encoded by Convolutional Neural Networks (CNNs) are of great interest, since they help to understand the underlying process hidden behind the black-box nature of these models. However, to explain the knowledge gathered in a given layer, they must decide which of the numerous filters to study, further assuming that each of them corresponds to a single feature. This, coupled with the redundancy of information, makes it difficult to ensure that the relevant characteristics are being analyzed. The above represents an important challenge and defines the aim and scope of our proposal. In this paper we present a novel method, named Explainable Layer Factor Analysis for CNNs (ELFA-CNNs), which models and describes with quality convolutional layers relying on factor analysis. Regarding contributions, ELFA obtains the essential underlying features, together with their correlation with the original filters, providing an accurate and well-founded summary. Through the factorial parameters we gain insights about the information learned, the connections between channels, and the redundancy of the layer, among others. To provide visual explanations in a similarly way to other methods, two additional proposals are made: a) Essential Feature Attribution Maps (EFAM) and b) intrinsic features inversion. The results prove the effectiveness of the developed general methods. They are evaluated in different CNNs (VGG-16, ResNet-50, and DeepLabv3+) on generic datasets (CIFAR-10, imagenette, and CamVid). We demonstrate that convolutional layers adequately fit a factorial model thanks to the new metrics presented for factor and fitting residuals (D1, D>, and Res, derive from covariance matrices). Moreover, knowledge about the deep image representations and the learning process is acquired, as well as reliable heat maps highlighting regions where essential features are located. This study effectively provides an explainable approach that can be applied to different CNNs and over different datasets.Item Artificial Intelligence Techniques for Automatic Detection of Peri‑implant Marginal Bone Remodeling in Intraoral Radiographs(Journal of Digital Imaging, 2023) Vera González, Vicente; Besada Portas, Eva; Pajares Martínsanz, Gonzalo; Gómez Silva, María José; Aliaga Vera, Ignacio Joaquín; Pedrera Canal, María; Vera, María; López-González, Clara Isabel; Gascó, EstherPeri-implantitis can cause marginal bone remodeling around implants. The aim is to develop an automatic image processing approach based on two artificial intelligence (AI) techniques in intraoral (periapical and bitewing) radiographs to assist dentists in determining bone loss. The first is a deep learning (DL) object-detector (YOLOv3) to roughly identify (no exact localization is required) two objects: prosthesis (crown) and implant (screw). The second is an image understanding-based (IU) process to fine-tune lines on screw edges and to identify significant points (intensity bone changes, intersections between screw and crown). Distances between these points are used to compute bone loss. A total of 2920 radiographs were used for training (50%) and testing (50%) the DL process. The mAP@0.5 metric is used for performance evaluation of DL considering periapical/bitewing and screws/crowns in upper and lower jaws, with scores ranging from 0.537 to 0.898 (sufficient because DL only needs an approximation). The IU performance is assessed with 50% of the testing radiographs through the t test statistical method, obtaining p values of 0.0106 (line fitting) and 0.0213 (significant point detection). The IU performance is satisfactory, as these values are in accordance with the statistical average/standard deviation in pixels for line fitting (2.75/1.01) and for significant point detection (2.63/1.28) according to the expert criteria of dentists, who establish the ground-truth lines and significant points. In conclusion, AI methods have good prospects for automatic bone loss detection in intraoral radiographs to assist dental specialists in diagnosing peri-implantitis.Item Analyzing and interpreting convolutional neural networks using latent space topology(Neurocomputing, 2024) López González, Clara Isabel; Gómez Silva, María José; Besada Portas, Eva; Pajares Martínsanz, GonzaloThe development of explainability methods for Convolutional Neural Networks (CNNs), under the growing framework of explainable Artificial Intelligence (xAI) for image understanding, is crucial due to neural networks success in contrast with their black box nature. However, usual methods focus on image visualizations and are inadequate to analyze the encoded contextual information (that captures the spatial dependencies of pixels considering their neighbors), as well as to explain the evolution of learning across layers without degrading the information. To address the latter, this paper presents a novel explanatory method based on the study of the latent representations of CNNs through their topology, and supported by Topological Data Analysis (TDA). For each activation layer after a convolution, the pixel values of the activation maps along the channels are considered latent space points. The persistent homology of this data is summarized via persistence landscapes, called Latent Landscapes. This provides a global view of how contextual information is being encoded, its variety and evolution, and allows for statistical analysis. The applicability and effectiveness of our approach is demonstrated by experiments conducted with CNNs trained on distinct datasets: (1) two U-Net segmentation models on RGB and pseudo-multiband images (generated by considering vegetation indices) from the agricultural benchmark CRBD were evaluated, in order to explain the difference in performance; and (2) a VGG-16 classification network on CIFAR-10 (RGB) was analyzed, showing how the information evolves within the network. Moreover, comparisons with state-of-the-art methods (Grad-CAM and occlusion) prove the consistency and validity of our proposal. It offers novel insights into the decision making process and helps to compare how models learn.Item Integration of object detection and semantic segmentation based on convolutional neural networks for navigation and monitoring of cyanobacterial blooms in lentic water scenes(Applied Soft Computing, 2024) Fredy Barrientos-Espillco; María J. Gómez-Silva; Besada Portas, Eva; Pajares Martínsanz, GonzaloLentic waters, such as lakes, lagoons, reservoirs, and wetlands are characterized by their absence of current. In recent decades, they have been threatened by pollution and scarcity due to various environmental factors. Therefore, they require frequent monitoring to ensure their health and purity, especially to control the proliferation of harmful cyanobacteria (pollutants). Machine Vision Systems (MVS) on board Autonomous Surface Vehicles (ASVs) is a good option for automatic image processing in this context. ASVs must navigate safely, and obstacle detection is essential. In addition, the segmentation of pollutants in water is crucial. We propose an architecture based on convolutional neural networks that integrates both object detection and semantic segmentation. The goal is to simultaneously extract all available global information to detect objects and amorphous textures (cyanobacterial patches and water bodies), considering their variations in size, pose, and appearance. The architecture includes two branches: object detection and semantic segmentation, sharing the same backbone and neck. We evaluate the model on our dataset and the results show that it can holistically understand lentic water scenes with high accuracy, and the integration of the attention mechanism improves its overall performance.Item Filter pruning for convolutional neural networks in semantic image segmentation(Neural Networks, 2024) López González, Clara Isabel; Gascó, Esther; Barrientos Espillco, Fredy; Besada Portas, Eva; Pajares Martínsanz, GonzaloThe remarkable performance of Convolutional Neural Networks (CNNs) has increased their use in real-time systems and devices with limited resources. Hence, compacting these networks while preserving accuracy has become necessary, leading to multiple compression methods. However, the majority require intensive iterative procedures and do not delve into the influence of the used data. To overcome these issues, this paper presents several contributions, framed in the context of explainable Artificial Intelligence (xAI): (a) two filter pruning methods for CNNs, which remove the less significant convolutional kernels; (b) a fine-tuning strategy to recover generalization; (c) a layer pruning approach for U-Net; and (d) an explanation of the relationship between performance and the used data. Filter and feature maps information are used in the pruning process: Principal Component Analysis (PCA) is combined with a next-convolution influence-metric, while the latter and the mean standard deviation are used in an importance score distribution-based method. The developed strategies are generic, and therefore applicable to different models. Experiments demonstrating their effectiveness are conducted over distinct CNNs and datasets, focusing mainly on semantic segmentation (using U-Net, DeepLabv3+, SegNet, and VGG-16 as highly representative models). Pruned U-Net on agricultural benchmarks achieves 98.7% parameters and 97.5% FLOPs drop, with a 0.35% gain in accuracy. DeepLabv3+ and SegNet on CamVid reach 46.5% and 72.4% parameters reduction and a 51.9% and 83.6% FLOPs drop respectively, with almost no decrease in accuracy. VGG-16 on CIFAR-10 obtains up to 86.5% parameter and 82.2% FLOPs decrease with a 0.78% accuracy gain.