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Métrologie ultrarapide : application aux dynamiques laser et à l'imagerie / Ultrafast metrology : application to the study of laser dynamics and for imagingHanzard, Pierre-Henry 11 October 2018 (has links)
Ce travail de thèse s’inscrit dans le cadre de la caractérisation optique à haute cadence en temps réel. Des outils de métrologie ultrarapides ont ainsi été utilisés pour l’étude d’une source laser impulsionnelle ainsi que pour l’imagerie de phénomènes physiques. La mise en place et la caractérisation temporelle d’une source laser impulsionnelle a permis l’observation d’événements anormalement intenses pour certains régimes de fonctionnement, et ces dynamiques ont pu être confirmées numériquement. La compréhension de ces phénomènes présente un intérêt fondamentalmais également pratique, notamment en vue de limiter les dommages optiques dans les sources laser. L’utilisation d’une technique d’imagerie appelée « imagerie par étirage temporel » a permis l’observation de jets liquides à une cadence de 80MHz. Reposant sur le principe de Transformée de Fourier Dispersive, cette technique permet de rendre compte de phénomènes non-répétitifs à des cadences élevées, et ainsi d’outrepasser les limitations imposées par les systèmes d’enregistrement conventionnels. La technique a également permis l’étude d’ondes de choc générées par ablation laser, et la détermination du profil de vitesse de l’onde de choc à travers la zone de mesure. Le phénomène de réflexion d’une onde de choc sur une paroi a également pu être observé. / This PhD work is dedicated to optical characterization in real time. Ultrafast metrology tools have thus been used to study a pulsed laser source and also for physical phenomena imaging. The implementation of a temporally well characterized pulsed laser source allowed the observation of events involving abnormally high intensity, the dynamics of which have also been numerically studied and confirmed. Understanding of these phenomena addresses a fundamental and interesting need to prevent optical damage in laser sources. The use of the imaging technique called “time-stretch imaging” allowed the imaging of liquid sprays at an 80MHz repetition rate. Based on Dispersive Fourier Transform, this technique enables the study of non-repetitive events at high sampling frequency, and thus goes beyond the performance of traditional imaging devices. This technique also allowed the tracking of shockwaves, and thus profiling the shockwave’s velocity variation through its propagation along a certain measuring distance. Shockwave reflection has also been observed.
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Audio editing in the time-frequency domain using the Gabor Wavelet TransformHammarqvist, Ulf January 2011 (has links)
Visualization, processing and editing of audio, directly on a time-frequency surface, is the scope of this thesis. More precisely the scalogram produced by a Gabor Wavelet transform is used, which is a powerful alternative to traditional techinques where the wave form is the main visual aid and editting is performed by parametric filters. Reconstruction properties, scalogram design and enhancements as well audio manipulation algorithms are investigated for this audio representation.The scalogram is designed to allow a flexible choice of time-frequency ratio, while maintaining high quality reconstruction. For this mean, the Loglet is used, which is observed to be the most suitable filter choice. Re-assignmentare tested, and a novel weighting function using partial derivatives of phase is proposed. An audio interpolation procedure is developed and shown to perform well in listening tests.The feasibility to use the transform coefficients directly for various purposes is investigated. It is concluded that Pitch shifts are hard to describe in the framework while noise thresh holding works well. A downsampling scheme is suggested that saves on operations and memory consumption as well as it speeds up real world implementations significantly. Finally, a Scalogram 'compression' procedure is developed, allowing the caching of an approximate scalogram.
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[en] ELASTIC TIME ALGORITHM FOR VIDEO IN MPEG-2 FLOWS / [pt] ALGORITMO DE AJUSTE ELÁSTICO PARA VÍDEO EM FLUXOS MPEG-2SERGIO ALVES CAVENDISH 09 August 2006 (has links)
[pt] Em apresentações hipermídia, umas das principais tarefas
coordenadas pelo
orquestrador da apresentação é a sincronização entre os
diversos objetos
componentes, que pode ser obtida através do ajuste
elástico do tempo de exibição
dos objetos. Esta técnica pode ser aplicada em tempo de
compilação, de forma a
manter os relacionamentos de sincronização especificados
pelo autor, ou em
tempo de apresentação, para prevenir qualquer descasamento
temporal causado
pelos ambientes de transmissão e de execução. Este
trabalho descreve um
conjunto de mecanismos para executar o ajuste elástico em
fluxos MPEG-2 de
Vídeo e de Sistemas, propondo algoritmos para a realização
da compressão e
expansão do tempo de exibição, do controle da ocupação do
buffer do
decodificador, da sincronização intermídia e da
reconstrução do relógio de
referência. Visando seu emprego em tempo de execução, todo
o processo de
ajuste é realizado diretamente no fluxo MPEG, sem qualquer
transcodificação. / [en] In hypermedia presentations, one of the main tasks
provided by the
orchestrator is the synchronization of all presentation
objects, which may be
achieved by elastic time adjustment of period of
exhibition of the objects, or
simply timescale adaptation. This technique can be applied
at compilation time, in
order to keep track of synchronism relationships specified
by authors, or at
presentation time, to prevent any temporal mismatch caused
by transmission or
execution environments. This work presents a set of
mechanisms to carry out
timescale adaptation in MPEG-2 Systems and Video streams,
proposing
algorithms to perform compression and expansion of
exhibition period, also called
playback dilation, rate control, inter-media
synchronization and clock
reconstruction. In order to be performed at execution
time, timescale operations
are realized directly in compressed MPEG-2 streams,
requiring no
transcodification.
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