Congressos (Departament de Tecnologies de la Informació i les Comunicacions)
http://hdl.handle.net/10230/16116
2024-03-18T19:38:34ZVariable penumbra soft shadows for mobile devices
http://hdl.handle.net/10230/59434
Variable penumbra soft shadows for mobile devices
Evans, Alun Thomas; Agenjo, Javier; Blat, Josep
In many applications of 3D graphics, shadows increase the believability and perceived quality of a scene. With the increase in power of workstation hardware, high-quality soft shadowing has become relatively common in many 3D desktop applications. In parallel, recent years have seen an increase in the availability and use of mobile and tablet based devices. The popularity of such devices is driving an increase in graphics intensive applications targeting the hardware, many of which will naturally require the use of shadowing algorithms. Yet the different architecture of graphics hardware of mobile devices restricts the implementation of many graphics algorithms, particularly those that require multiple references to a texture, such as common shadowing techniques. In this paper, we discuss effective shadowing on mobile devices. We show that even small-kernel Percentage Closer Filtering (PCF) soft shadows provide unacceptable framerates on mobile GPUs, but also how mip-chain dilation o f the edges of a shadow map allows improvement performance to acceptable levels. Finally, we extend this technique by quantizing the strength of the detected edge to implement variable penumbra shadowing based on occluder distance.
Comunicació presentada a la 9th International Conference on Computer Graphics Theory and Applications (VISIGRAPP 2014), celebrada del 5 al 8 de gener de 2014 a Lisboa, Portugal.
2014-01-01T00:00:00ZA multiclass anisotropic Mumford-Shah functional for segmentation of d-dimensional vectorial images
http://hdl.handle.net/10230/59400
A multiclass anisotropic Mumford-Shah functional for segmentation of d-dimensional vectorial images
Garamendi, Juan Francisco; Schiavi, Emanuele
We present a general model for multi-class segmentation of multi-channel digital images. It is based on the minimization of an anisotropic version of the Mumford-Shah energy functional in the class of piecewise constant functions. In the framework of geometric measure theory we use the concept of common interphases between regions (classes) and the value of the jump discontinuities of the (weak) solution between adjacent regions in order to define a minimal partition energy functional. The resulting problem is non-smooth and non-convex. Non-smoothness is dealt with highlighting the relationship of the proposed model with the well known Rudin, Osher and Fatemi model for image denoising when piecewise constant solutions (i.e partitions) are considered. Non-convexity is tackled with an optimal threshold of the ROF solution which we which generalize to multi-channel images through a probabilistic clustering. The optimal solution is then computed with a fixed point iteration. The result ing algorithm is described and results are presented showing the successful application of the method to Light Field (LF) images.
Comunicació presentada a la 12th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISIGRAPP 2017), celebrada del 27 de febrer l'1 de març de 2017 a Porto, Portugal.
2017-01-01T00:00:00ZHaemodynamic changes in the fetal circulation post-connection to an artificial placenta: a computational modelling study
http://hdl.handle.net/10230/59303
Haemodynamic changes in the fetal circulation post-connection to an artificial placenta: a computational modelling study
Villanueva, M. Inmaculada; López, Marc; Sánchez, Sergio; García Cañadilla, Patricia, 1985-; Randanne, Paula C.; Hawkins, Ameth; Eixarch, Elisenda; Bonet-Carne, Elisenda; Gratacós Solsona, Eduard; Crispi Brillas, Fàtima; Bijnens, Bart; Bernardino Perez, Gabriel
Artificial placenta (AP) is a promising approach to improve survival in extremely premature fetuses, removing them from the uterus and replacing the placenta by an external oxygenator. In in vivo experiments with lambs, haemodynamic changes were observed in the umbilical artery (UA) post-connection to the AP: decrease in flow pulsatility index (PI), increase in mean pressure and heart rate, and flatter diastolic flow with a secondary peak.
Computational models can help to understand the causes of observed phenomena. Therefore, the clinical objective of this work was to investigate the causes of the aforementioned changes in UA velocity, while the methodological objective was to implement a computational model capable of reproducing the behaviour of an AP.
We used a closed lumped model of the whole fetal circulation, modified to include the AP, and tested the haemodynamic changes in the UA after altering heart rate and AP’s resistance and compliance. We also added a simple wave reflection model and studied its effect on pressure and flow traces. We found that reducing AP’s resistance increased mean flow, and reducing compliance decreased velocity PI. When adding the reflection model, the flatter diastolic flow observed in the UA was reproduced.
This study suggests that the observed haemodynamics changes in the UA post-connection to the AP are due to a combination of decreased compliance and resistance, as well as wave reflections from components within the AP circuit.
Comunicació presentada a 13th International Workshop, STACOM 2022, Held in Conjunction with MICCAI 2022, celebrada el 18 de setembre de 2022 a Singapur.
2022-01-01T00:00:00ZComputational modelling of the cardiovascular system for the non-invasive diagnosis of portal hypertension
http://hdl.handle.net/10230/59302
Computational modelling of the cardiovascular system for the non-invasive diagnosis of portal hypertension
Villanueva, M. Inmaculada; García Cañadilla, Patricia, 1985-; Camara, Oscar; Garcia-Criado, Angeles; Campreciós, Genís; Perez-Campuzano, Valeria; Hernandez-Gea, Virgina; Turon, Fanny; Baiges Aznar, Anna; Lopez Sainz, Angela; García-Pagan, Juan Carlos; Bijnens, Bart; Bernardino Perez, Gabriel
Cirrhosis is a prevalent chronic liver disease that causes scarring of the liver, leading to altered mechanics and impaired function. One of its most severe complications is portal hypertension, characterised by an increase in portal vein pressure, associated with abnormal blood flow dynamics. Portal hypertension is usually diagnosed by measuring the hepatic venous pressure gradient (HVPG) through invasive catheterisation. Computational models can help to understand the causes of observed phenomena and assess certain variables that are challenging to measure without invasive procedures. Therefore, the aim of this study was to use a 0D model of the cardiovascular system to study portal hypertension and its haemodynamic effects in the circulation. A sensitivity analysis was conducted to assess the impact of different variables on the model. In addition, the model was personalised based on hepatic Doppler waveforms from two patients, one with elevated HVPG (and cirrhosis) and the other with normal HVPG (and hepatitis). The model-based haemodynamic parameters were compared to the invasive haemodynamic measurements. This study provides insight into how cirrhosis alters haemodynamics and demonstrates the potential of employing computational models of the cardiovascular system to understand haemodynamic changes in individual patients.
Comunicació presentada a 12th International Conference, FIMH 2023, celebrada del 19 al 22 de juny de 2023 a Lió, França.
2023-01-01T00:00:00Z