Imperial College London
Portrait Picture

Dr. Ayush Bhandari

Faculty of Engineering, Department of Electrical and Electronic Engineering

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 6233a.bhandari Website

 
 
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Location

 

802Electrical EngineeringSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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54 results found

Bhandari A, Krahmer F, Raskar R, 2018, Unlimited Sampling of Sparse Sinusoidal Mixtures, IEEE International Symposium on Information Theory (ISIT), Publisher: IEEE, Pages: 336-340

Conference paper

Bhandari A, Krahmer F, Raskar R, 2017, On unlimited sampling, 2017 International Conference on Sampling Theory and Applications (SampTA), Publisher: IEEE, Pages: 31-35

Shannon's sampling theorem provides a link between the continuous and the discrete realms stating that bandlimited signals are uniquely determined by its values on a discrete set. This theorem is realized in practice using so called analog-to-digital converters (ADCs). Unlike Shannon's sampling theorem, the ADCs are limited in dynamic range. Whenever a signal exceeds some preset threshold, the ADC saturates, resulting in aliasing due to clipping. The goal of this paper is to analyze an alternative approach that does not suffer from these problems. Our work is based on recent developments in ADC design, which allow for ADCs that reset rather than to saturate, thus producing modulo samples. An open problem that remains is: Given such modulo samples of a bandlimited function as well as the dynamic range of the ADC, how can the original signal be recovered and what are the sufficient conditions that guarantee perfect recovery? In this paper, we prove such sufficiency conditions and complement them with a stable recovery algorithm. Our results are not limited to certain amplitude ranges, in fact even the same circuit architecture allows for the recovery of arbitrary large amplitudes as long as some estimate of the signal norm is available when recovering. Numerical experiments that corroborate our theory indeed show that it is possible to perfectly recover function that takes values that are orders of magnitude higher than the ADC's threshold.

Conference paper

Bhandari A, Blu T, 2017, FRI SAMPLING AND TIME-VARYING PULSES: SOME THEORY AND FOUR SHORT STORIES, IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Publisher: IEEE, Pages: 3804-3808, ISSN: 1520-6149

Conference paper

Bhandari A, Bourquard A, Raskar R, 2017, SAMPLING WITHOUT TIME: RECOVERING ECHOES OF LIGHT VIA TEMPORAL PHASE RETRIEVAL, IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Publisher: IEEE, Pages: 3829-3833, ISSN: 1520-6149

Conference paper

Bhandari A, Raskar R, 2016, Signal processing for time-of-flight imaging sensors: an introduction to inverse problems in computational 3-D imaging, IEEE Signal Processing Magazine, Vol: 33, Pages: 45-58, ISSN: 1053-5888

Time-of-flight (ToF) sensors offer a cost-effective and realtime solution to the problem of three-dimensional (3-D) imaging-a theme that has revolutionized our sceneunderstanding capabilities and is a topic of contemporary interest across many areas of science and engineering. The goal of this tutorial-style article is to provide a thorough understanding of ToF imaging systems from a signal processing perspective that is useful to all application areas. Starting with a brief history of the ToF principle, we describe the mathematical basics of the ToF image-formation process, for both time- and frequency-domain, present an overview of important results within the topic, and discuss contemporary challenges where this emerging area can benefit from the signal processing community. In particular, we examine case studies where inverse problems in ToF imaging are coupled with signal processing theory and methods, such as sampling theory, system identification, and spectral estimation, among others. Through this exposition, we hope to establish that ToF sensors are more than just depth sensors; depth information may be used to encode other forms of physical parameters, such as, the fluorescence lifetime of a biosample or the diffusion coefficient of turbid/scattering medium. The MATLAB scripts and ToF sensor data used for reproducing figures in this article are available via the author?s webpage: http://www.mit.edu/~ayush/Code.

Journal article

Feigin M, Bhandari A, Izadi S, Rhemann C, Schmidt M, Raskar Ret al., 2016, Resolving Multipath Interference in Kinect: An Inverse Problem Approach, IEEE SENSORS JOURNAL, Vol: 16, Pages: 3419-3427, ISSN: 1530-437X

Journal article

Bhandari A, Wallace AM, Raskar R, 2016, Super-resolved time-of-flight sensing via FRI sampling theory, 2016 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), Publisher: IEEE

Conference paper

Bhandari A, Eldar YC, 2016, A swiss army knife for finite rate of innovation sampling theory, 2016 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), Publisher: IEEE

Conference paper

Bhandari A, Bourquard A, Izadi S, Raskar Ret al., 2016, TIME-RESOLVED IMAGE DEMIXING, 41st IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), Publisher: IEEE, Pages: 4483-4487, ISSN: 1520-6149

Conference paper

Bhandari A, Barsi C, Raskar R, 2015, Blind and reference-free fluorescence lifetime estimation via consumer time-of-flight sensors, Optica, Vol: 2, Pages: 965-973, ISSN: 2334-2536

Fluorescence lifetime imaging (FLI) is a popular method for extracting useful information that is otherwise unavailable from a conventional intensity image. Usually, however, it requires expensive equipment, is often limited to either distinctly frequency- or time-domain modalities, and demands calibration measurements and precise knowledge of the illumination signal. Here, we present a generalized time-based, cost-effective method for estimating lifetimes by repurposing a consumer-grade time-of-flight sensor. By developing mathematical theory that unifies time- and frequency-domain approaches, we can interpret a time-based signal as a combination of multiple frequency measurements. We show that we can estimate lifetimes without knowledge of the illumination signal and without any calibration. We experimentally demonstrate this blind, reference-free method using a quantum dot solution and discuss the method’s implementation in FLI applications.

Journal article

Feigin M, Whyte R, Bhandari A, Dorington A, Raskar Ret al., 2015, Modeling "wiggling" as a multi-path interference problem in AMCW ToF imaging, OPTICS EXPRESS, Vol: 23, Pages: 19213-19225, ISSN: 1094-4087

Journal article

Bhandari A, Eldar YC, Raskar R, 2015, SUPER-RESOLUTION IN PHASE SPACE, 40th IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Publisher: IEEE, Pages: 4155-4159, ISSN: 1520-6149

Conference paper

Bhandari A, Feigin M, Izadi S, Rhemann C, Schmidt M, Raskar Ret al., 2014, Resolving multipath interference in Kinect: An inverse problem approach, 2014 IEEE Sensors, Publisher: IEEE

Conference paper

Bhandari A, Kadambi A, Whyte R, Barsi C, Feigin M, Dorrington A, Raskar Ret al., 2014, Resolving multipath interference in time-of-flight imaging via modulation frequency diversity and sparse regularization, Optics Letters, Vol: 39, Pages: 1705-1708, ISSN: 0146-9592

Time-of-flight (ToF) cameras calculate depth maps by reconstructing phase shifts of amplitude-modulated signals. For broad illumination of transparent objects, reflections from multiple scene points can illuminate a given pixel, giving rise to an erroneous depth map. We report here a sparsity-regularized solution that separates interfering components using multiple modulation frequency measurements. The method maps ToF imaging to the general framework of spectral estimation theory and has applications in improving depth profiles and exploiting multiple scattering.

Journal article

Bhandari A, Barsi C, Whyte R, Kadambi A, Das A, Dorrington A, Raskar Ret al., 2014, Coded Time-of-Flight Imaging for Calibration Free Fluorescence Lifetime Estimation, Imaging Systems and Applications, Publisher: OSA

Conference paper

Kadambi A, Bhandari A, Raskar R, 2014, 3D Depth Cameras in Vision: Benefits and Limitations of the Hardware, Computer Vision and Machine Learning with RGB-D Sensors, Publisher: Springer International Publishing, Pages: 3-26, ISBN: 9783319086507

Book chapter

Kadambi A, Bhandari A, Whyte R, Dorrington A, Raskar Ret al., 2014, Demultiplexing Illumination via Low Cost Sensing and Nanosecond Coding, 6th IEEE International Conference on Computational Photography (ICCP), Publisher: IEEE, ISSN: 2164-9774

Conference paper

Bhandari A, Kadambi A, Raskar R, 2014, SPARSE LINEAR OPERATOR IDENTIFICATION WITHOUT SPARSE REGULARIZATION ? APPLICATIONS TO MIXED PIXEL PROBLEM IN TIME-OF-FLIGHT/RANGE IMAGING, IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), Publisher: IEEE, ISSN: 1520-6149

Conference paper

Kadambi A, Whyte R, Bhandari A, Streeter L, Barsi C, Dorrington A, Raskar Ret al., 2013, Coded Time of Flight Cameras: Sparse Deconvolution to Address Multipath Interference and Recover Time Profiles, ACM TRANSACTIONS ON GRAPHICS, Vol: 32, ISSN: 0730-0301

Journal article

Bhandari A, Zayed AI, 2012, Shift-Invariant and Sampling Spaces Associated With the Fractional Fourier Transform Domain, IEEE TRANSACTIONS ON SIGNAL PROCESSING, Vol: 60, Pages: 1627-1637, ISSN: 1053-587X

Journal article

Bhandari A, Marziliano P, 2010, Sampling and Reconstruction of Sparse Signals in Fractional Fourier Domain, IEEE SIGNAL PROCESSING LETTERS, Vol: 17, Pages: 221-224, ISSN: 1070-9908

Journal article

Bhandari A, Marziliano P, 2010, Fractional Delay Filters Based on Generalized Cardinal Exponential Splines, IEEE SIGNAL PROCESSING LETTERS, Vol: 17, Pages: 225-228, ISSN: 1070-9908

Journal article

Bhandari A, Khare V, Santhosh J, Anand Set al., 2007, Wavelet based compression technique of Electro-oculogram signals, 3rd Kuala Lumpur International Conference on Biomedical Engineering 2006 (BioMed 2006), Publisher: SPRINGER, Pages: 440-+, ISSN: 1680-0737

Conference paper

Bhandari A, Khare V, Trikha M, Anand Set al., 2006, Wavelet based novel technique for signal conditioning of electro-oculogram signals, Annual IEEE India Conference, Publisher: IEEE, Pages: 525-+, ISSN: 2325-940X

Conference paper

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