Images par seconde

Résumé

Le nombre d’images par seconde ou cadence d'images à la seconde en abrégé, IPS ou i/s est une unité de mesure correspondant au nombre d's enregistrées ou affichées en une seconde par un dispositif, dans un signal vidéo ou optique. La valeur de la fréquence d’affichage peut également s'exprimer en hertz. Sur beaucoup d'équipements audiovisuels, le nombre d'images par seconde est généralement décrit en anglais par l'expression : frame rate, frames per second ou FPS, littératement, la cadence d'image par seconde. La cadence image est employée pour le balayage progressif, comme pour le balayage entrelacé. Plus le nombre d'images est élevé, plus l'animation parait fluide. Ce principe affecte notamment l'effet de papillotement. Cadence et fluidité La cadence d'au moins 16 images par seconde est requise pour générer l'illusion d'un mouvement fluide mais le nombre d'images dépend beaucoup de la nature et de la complexité des images successives (voir le folioscope). Pour le ci

Source officielle

https://fr.wikipedia.org/wiki/Images_par_seconde

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Light microscopy is a tool of paramount importance for biologists and has been constantly improved for the past four centuries. Despite many recent developments, microscopy techniques still require improvement, especially to reach better temporal and spectral resolutions. In particular, many high-end microscopes favor mostly spatial resolution, at the expense of the latter two types of resolution. In this thesis, we present methods based on the use of active illumination and computational algorithms to increase temporal and spectral resolutions of microscopes. Our methods aim to provide users with the flexibility to chose, within a single instrument, which type of resolution is to be favored based on the application at hand. More generally, our approach has fundamental implications on the signal sensing procedure, allowing, for example, to mitigate temporal aliasing in sequences of images. Our first method performs temporal super-resolution imaging of monochrome scenes using a hue-encoded shutter. By making use of an active multi-spectral illumination, temporal information is encoded in the hue of the acquisitions. We characterize the method showing a resolution improvement of 2.8 and an increase of frame-rate of a factor 3. We demonstrate the applicability of our method to bright-field transmission microscopy by applying the method to the beating heart of a zebrafish.We then extend this method to fluorescence microscopy. We add a temporal regularization term to make the method robust to fluorescent labelings inhomogeneities. We present an application of the method to the beating heart of a zebrafish that emits fluorescent light of two different colors. Implementing our method within a light-sheet microscope allows us to reconstruct 3D+time videos of the beating heart at twice the acquisition frame-rate. Our second method offers a way to perform temporal generalized sampling by computing simultaneous inner products with the sampled signal. Similarly to the first method, we take advantage of working with multiple illumination hues to compute as many simultaneous inner products, which we retrieve via an unmixing procedure. We use equivalent basic and dual B-splines representations to ensure having finite-length and positive pre-filters, as well as finite-support reconstruction functions. We show applications of our method to a fast rotating target, as well as to the beating heart of a zebrafish, both in transmission and fluorescence microscopy. Finally, we introduce a method to perform spectral imaging of repeating processes, such as the beating heart. The method sequentially acquires multiple movies with various filters, performs temporal registration of all movies and reconstructs a spectral movie through solving of a spectral unmixing problem, pixel by pixel, at each time point. We characterize the method and show a median error of approximately 10%, by comparing reconstructions on a static sample from our method with measurements obtained with a spectrometer. We then perform validation by comparing static reconstructions with dynamic ones of the same sample. We demonstrate the potential of the method to microscopy by performing spectral imaging of the beating heart of a zebrafish. Taken together, these methods offer a versatile toolbox to improve the temporal or spectral resolution in both bright field and fluorescence microscopy, which we foresee could be directly implemented in a number of specialized instruments.

EPFL2020

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Temporal resolution doubling in fluorescence light-sheet microscopy via a hue-encoded shutter and regularization

Christian Jaques, Michael Stefan Daniel Liebling

Studying dynamic biological processes, such as heart development and function in zebrafish embryos, often relies on multi-channel fluorescence labeling to distinguish multiple anatomical features, yet also demands high frame rates to capture rapid cell motions. Although a recently proposed method for imaging dynamic samples in transmission or reflection allows to conveniently switch between color imaging or boosting the frame rate by use of spectrally-encoded, temporally-modulated illumination sequences and a hue-encoded shutter (hue-encode shutter method, HESM), the technique is not applicable directly in fluorescence microscopy, where the emitted light spectrum is mostly independent of the excitation wavelength. In this paper, we extend HESM by using samples labeled with multiple fluorophores, whose emission signal can either be used to distinguish multiple anatomical features when imaged in multi-channel mode or, if the fluorophores are co-localized in a dynamic tissue, to increase the frame rate via HESM. We detail the necessary steps to implement this method in a two-color light-sheet microscope to image the beating heart of a zebrafish embryo. Specifically, we propose an adapted laser modulation scheme for illumination, we identify caveats in choosing a suitable multi-color fluorophore labeling strategy, and derive an l(1)-regularized reconstruction technique that is sufficiently robust to handle the low signal-to-noise ratio and labeling inhomogeneities in the fluorescence images at hand. Using the case of a beating heart in a zebrafish embryo, we experimentally show an increase in the frame rate by a factor two while preserving the ability to image static features labeled in distinct channels, thereby demonstrating the applicability of HESM to fluorescence. With a suitable illumination setup and fluorescent labeling, the method could generalize to other applications where flexibility between multiple channel and high-speed fluorescence imaging is desirable. For fluorophores that are not co-localized, the imaging system is similar to a conventional light sheet microscope. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

2020

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Mapping Biological Current Densities With Ultrafast Acoustoelectric Imaging: Application to the Beating Rat Heart

Pierre-Marc Jean Marie Dansette

Ultrafast acoustoelectric imaging (UAI) is a novel method for the mapping of biological current densities, which may improve the diagnosis and monitoring of cardiac activation diseases such as arrhythmias. This paper evaluates the feasibility of performing UAI in beating rat hearts. A previously described system based on a 256-channel ultrasound research platform fitted with a 5-MHz linear array was used for simultaneous UAI, ultrafast B-mode, and electrocardiogram (ECG) recordings. In this paper, rat hearts (n = 4) were retroperfused within a Langendorff isolated heart system. A pair of Ag/Cl electrodes were positioned on the epicardium to simultaneously record ECG and UAI signals for imaging frame rates of up to 1000 Hz and a mechanical index of 1.3. To account for the potential effect of motion on the UAI maps, acquisitions for n = 3 hearts were performed with and without suppression of the mechanical contraction using 2,3-butanedione monoxime. Current densities were detected for all four rats in the region of the atrio-ventricular node, with an average contrast-to-noise ratios of 12. The UAI signals' frequency matched the sinus rhythm, even without mechanical contraction, suggesting that the signals measured correspond to physiological electrical activation. UAI signals appeared at the apex and within the ventricular walls with a delay estimated at 29 ms. Finally, the signals from different electrode positions along the myocardium wall showed the possibility of mapping the electrical activation throughout the heart. These results show the potential of UAI for cardiac activation mapping in vivo and in real time.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2019

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Temporal resolution doubling in fluorescence light-sheet microscopy via a hue-encoded shutter and regularization

Christian Jaques, Michael Stefan Daniel Liebling

2020

EPFL2020