375 research outputs found
The deep structure of Gaussian scale space images
In order to be able to deal with the discrete nature of images in a continuous way, one can use results of the mathematical field of 'distribution theory'. Under almost trivial assumptions, like 'we know nothing', one ends up with convolving the image with a Gaussian filter.
In this manner scale is introduced by means of the filter's width. The ensemble of the image and its convolved versions at al scales is called a 'Gaussian scale space image'. The filter's main property is that the scale derivative equals the Laplacean of the spatial variables: it is the Greens function of the so-called Heat, or Diffusion, Equation.
The investigation of the image all scales simultaneously is called 'deep structure'.
In this thesis I focus on the behaviour of the elementary topological items 'spatial critical points' and 'iso-intensity manifolds'.
The spatial critical points are traced over scale. Generically they are annihilated and sometimes created pair wise, involving extrema and saddles. The locations of these so-called 'catastrophe events' are calculated with sub-pixel precision.
Regarded in the scale space image, these spatial critical points form one-dimensional manifolds, the so-called critical curves.
A second type of critical points is formed by the scale space saddles. They are the only possible critical points in the scale space image. At these points the iso-intensity manifolds exhibit special behaviour: they consist of two touching parts, of which one intersects an extremum that is part of the critical curve containing the scale space saddle.
This part of the manifold uniquely assigns an area in scale space to this extremum. The remaining part uniquely assigns it to 'other structure'.
Since this can be repeated, automatically an algorithm is obtained that reveals the 'hidden' structure present in the scale space image. This topological structure can be hierarchically presented as a binary tree, enabling one to (de-)select parts of it, sweeping out parts, simplify, etc.
This structure can easily be projected to the initial image resulting in an uncommitted 'pre-segmentation': a segmentation of the image based on the topological properties without any user-defined parameters or whatsoever.
Investigation of non-generic catastrophes shows that symmetries can easily be dealt with. Furthermore, the appearance of creations is shown to be nothing but (instable) protuberances at critical curves.
There is also biological inspiration for using a Gaussian scale space, since the visual system seems to use Gaussian-like filters: we are able of seeing and interpreting multi-scale
Combining Background Subtraction Algorithms with Convolutional Neural Network
Accurate and fast extraction of foreground object is a key prerequisite for a
wide range of computer vision applications such as object tracking and
recognition. Thus, enormous background subtraction methods for foreground
object detection have been proposed in recent decades. However, it is still
regarded as a tough problem due to a variety of challenges such as illumination
variations, camera jitter, dynamic backgrounds, shadows, and so on. Currently,
there is no single method that can handle all the challenges in a robust way.
In this letter, we try to solve this problem from a new perspective by
combining different state-of-the-art background subtraction algorithms to
create a more robust and more advanced foreground detection algorithm. More
specifically, an encoder-decoder fully convolutional neural network
architecture is trained to automatically learn how to leverage the
characteristics of different algorithms to fuse the results produced by
different background subtraction algorithms and output a more precise result.
Comprehensive experiments evaluated on the CDnet 2014 dataset demonstrate that
the proposed method outperforms all the considered single background
subtraction algorithm. And we show that our solution is more efficient than
other combination strategies
Style-transfer GANs for bridging the domain gap in synthetic pose estimator training
Given the dependency of current CNN architectures on a large training set,
the possibility of using synthetic data is alluring as it allows generating a
virtually infinite amount of labeled training data. However, producing such
data is a non-trivial task as current CNN architectures are sensitive to the
domain gap between real and synthetic data. We propose to adopt general-purpose
GAN models for pixel-level image translation, allowing to formulate the domain
gap itself as a learning problem. The obtained models are then used either
during training or inference to bridge the domain gap. Here, we focus on
training the single-stage YOLO6D object pose estimator on synthetic CAD
geometry only, where not even approximate surface information is available.
When employing paired GAN models, we use an edge-based intermediate domain and
introduce different mappings to represent the unknown surface properties. Our
evaluation shows a considerable improvement in model performance when compared
to a model trained with the same degree of domain randomization, while
requiring only very little additional effort
Generalization of Fitness Exercise Recognition from Doppler Measurements by Domain-adaption and Few-Shot Learning
In previous works, a mobile application was developed using an unmodified
commercial off-the-shelf smartphone to recognize whole-body exercises. The
working principle was based on the ultrasound Doppler sensing with the device
built-in hardware. Applying such a lab-environment trained model on realistic
application variations causes a significant drop in performance, and thus
decimate its applicability. The reason of the reduced performance can be
manifold. It could be induced by the user, environment, and device variations
in realistic scenarios. Such scenarios are often more complex and diverse,
which can be challenging to anticipate in the initial training data. To study
and overcome this issue, this paper presents a database with controlled and
uncontrolled subsets of fitness exercises. We propose two concepts to utilize
small adaption data to successfully improve model generalization in an
uncontrolled environment, increasing the recognition accuracy by two to six
folds compared to the baseline for different users.Comment: accepted at International Conference on Pattern Recognition (ICPR)
workshop 202
Exploring Adversarial Examples: Patterns of One-Pixel Attacks
Failure cases of black-box deep learning, e.g. adversarial examples, might
have severe consequences in healthcare. Yet such failures are mostly studied in
the context of real-world images with calibrated attacks. To demystify the
adversarial examples, rigorous studies need to be designed. Unfortunately,
complexity of the medical images hinders such study design directly from the
medical images. We hypothesize that adversarial examples might result from the
incorrect mapping of image space to the low dimensional generation manifold by
deep networks. To test the hypothesis, we simplify a complex medical problem
namely pose estimation of surgical tools into its barest form. An analytical
decision boundary and exhaustive search of the one-pixel attack across multiple
image dimensions let us localize the regions of frequent successful one-pixel
attacks at the image space.Comment: Figure 4 corrected from published Version to correct y-axis label
Demographic Bias in Presentation Attack Detection of Iris Recognition Systems
With the widespread use of biometric systems, the demographic bias problem
raises more attention. Although many studies addressed bias issues in biometric
verification, there are no works that analyze the bias in presentation attack
detection (PAD) decisions. Hence, we investigate and analyze the demographic
bias in iris PAD algorithms in this paper. To enable a clear discussion, we
adapt the notions of differential performance and differential outcome to the
PAD problem. We study the bias in iris PAD using three baselines (hand-crafted,
transfer-learning, and training from scratch) using the NDCLD-2013 database.
The experimental results point out that female users will be significantly less
protected by the PAD, in comparison to males.Comment: accepted for publication at EUSIPCO202
Extension of Dictionary-Based Compression Algorithms for the Quantitative Visualization of Patterns from Log Files
Many services today massively and continuously produce log files of different
and varying formats. These logs are important since they contain information
about the application activities, which is necessary for improvements by
analyzing the behavior and maintaining the security and stability of the
system. It is a common practice to store log files in a compressed form to
reduce the sheer size of these files. A compression algorithm identifies
frequent patterns in a log file to remove redundant information. This work
presents an approach to detect frequent patterns in textual data that can be
simultaneously registered during the file compression process with low
consumption of resources. The log file can be visualized with the possibility
to explore the extracted patterns using metrics based on such properties as
frequency, length and root prefixes of the acquired pattern. This allows an
analyst to gain the relevant insights more efficiently reducing the need for
manual labor-intensive inspection in the log data. The extension of the
implemented dictionary-based compression algorithm has the advantage of
recognizing patterns in log files of any format and eliminates the need to
manually perform preparation for any preprocessing of log files.Comment: submitted to EuroVA 202
Optimizations for Passive Electric Field Sensing
Passive electric field sensing can be utilized in a wide variety of application areas, although it has certain limitations. In order to better understand what these limitations are and how countervailing measures to these limitations could be implemented, this paper contributes an in-depth discussion of problems with passive electric field sensing and how to bypass or solve them. The focus lies on the explanation of how commonly known signal processing techniques and hardware build-up schemes can be used to improve passive electric field sensors and the corresponding data processing
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