Search results for "CONTRAST"

Automatic fringe pattern enhancement using truly adaptive period-guided bidimensional empirical mode decomposition.

2020

Fringe patterns encode the information about the result of a measurement performed via widely used optical full-field testing methods, e.g., interferometry, digital holographic microscopy, moiré techniques, structured illumination etc. Affected by the optical setup, changing environment and the sample itself fringe patterns are often corrupted with substantial noise, strong and uneven background illumination and exhibit low contrast. Fringe pattern enhancement, i.e., noise minimization and background term removal, at the pre-processing stage prior to the phase map calculation (for the measurement result decoding) is therefore essential to minimize the jeopardizing effect the mentioned error…

Different mechanisms underlie implicit visual statistical learning in honey bees and humans

2020

International audience; The ability of developing complex internal representations of the environment is considered a crucial antecedent to the emergence of humans’ higher cognitive functions. Yet it is an open question whether there is any fundamental difference in how humans and other good visual learner species naturally encode aspects of novel visual scenes. Using the same modified visual statistical learning paradigm and multielement stimuli, we investigated how human adults and honey bees ( Apis mellifera ) encode spontaneously, without dedicated training, various statistical properties of novel visual scenes. We found that, similarly to humans, honey bees automatically develop a comp…

Atrial activity extraction for atrial fibrillation analysis using blind source separation.

2004

This contribution addresses the extraction of atrial activity (AA) from real electrocardiogram (ECG) recordings of atrial fibrillation (AF). We show the appropriateness of independent component analysis (ICA) to tackle this biomedical challenge when regarded as a blind source separation (BSS) problem. ICA is a statistical tool able to reconstruct the unobservable independent sources of bioelectric activity which generate, through instantaneous linear mixing, a measurable set of signals. The three key hypothesis that make ICA applicable in the present scenario are discussed and validated: 1) AA and ventricular activity (VA) are generated by sources of independent bioelectric activity; 2) AA …

Does Regression Discontinuity Design Work? Evidence from Random Election Outcomes

2014

We use data for 198121 candidates and 1351 random election outcomes to estimate the effect of incumbency status on future electoral success. We find no evidence of incumbency advantage using data on randomized elections. In contrast, regression discontinuity design, using optimal bandwidths, produces a positive and significant incumbency effect. Using even narrower bandwidths aligns the results with those obtained using the randomized elections. So does the bias-correction of Calonico et al. (forthcoming). Standard validity tests are not useful in detecting the problems with the optimal bandwidths. The appropriate bandwidth seems narrower in larger elections and is thus context specific.

Comparison of Statistical Methods for the Detection of Contrast Material in Echocardiographic Image Sequences

1987

Ultrasonic imaging of the heart is a diagnostic tool which is increasingly used in cardiology. In addition to the representation of important anatomical information two dimensional images provided by mechanical or electronically steered sector scanners can be used for the extraction of functional parameters of the heart (as e.g. enddiastolic volume or ejection fraction). A poor definition of the endocardial border especially resulting from the noisy appearance of the images and from qualitatively restricted echocardiograms leads to uncertainties in the quantitative analysis and therefore requires refined methods for the determination of functional parameters. Our investigations which are ba…

Divisive normalization image quality metric revisited.

2010

Structural similarity metrics and information-theory-based metrics have been proposed as completely different alternatives to the traditional metrics based on error visibility and human vision models. Three basic criticisms were raised against the traditional error visibility approach: (1) it is based on near-threshold performance, (2) its geometric meaning may be limited, and (3) stationary pooling strategies may not be statistically justified. These criticisms and the good performance of structural and information-theory-based metrics have popularized the idea of their superiority over the error visibility approach. In this work we experimentally or analytically show that the above critic…

Mobile phone based laser speckle contrast imager for assessment of skin blood flow

2014

Assessment of skin blood flow is of interest for evaluation of skin viability as well as for reflection of the overall condition of the circulatory system. Laser Doppler perfusion imaging (LDPI) and laser speckle contrast imaging (LASCI) are optical techniques used for assessment of skin perfusion. However, these systems are still too expensive and bulky to be widely available. Implementation of such techniques as connection kits for mobile phones have a potential for primary diagnostics. In this work we demonstrate simple and low cost LASCI connection kit for mobile phone and its comparison to laser Doppler perfusion imager. Post-occlusive hyperemia and local thermal hyperemia tests are us…

MULTISPECTRAL VENOUS IMAGES ANALYSIS FOR OPTIMUM ILLUMINATION SELECTION

2013

International audience; Intravenous (IV) catheterization is the most important phase in medical practices of daily life. It is hard to localize veins in patients who have deep veins, minor age or dark skin; hence multiple attempts become indispensable for proper catheterization in such cases. Near Infrared (NIR) Imaging allow to visualize the veins underneath the skin of persons having non-visibility of veins problem. This paper reports the pre-selection of illuminants that ensure best veins/tissues contrast for patients having different skin tone. The sample subjects have been divided in four different classes based on the Luminance value of their skin tone in order to extract the best ill…

The Wilson-Cowan model describes Contrast Response and Subjective Distortion

2017

Evaluation of the registration of temporal series of contrast-enhanced perfusion magnetic resonance 3D images of the liver.

2011

The registration of 2D and 3D images is one of the key tasks in medical image processing and analysis. Accurate registration is a crucial preprocessing step for many tasks; consequently, the evaluation of its accuracy becomes necessary. Unfortunately, this is a difficult task, especially when no golden pattern (true result) is available and when the signal values may have changed between successive images to be registered. This is the case this paper deals with: we have a series of 3D images, magnetic resonance images (MRI) of the liver and adjacent areas that have to be registered. They have been taken while a contrast is diffused through the liver tissue, so intensity of each observed poi…