Photographie | EPFL Graph Search

vignette|Mère migrante (Migrant Mother), photographie de Dorothea Lange, 1936. thumb|redresse|Dali Atomicus, photographie de Philippe Halsman mettant en scène Salvador Dalí. vignette|Une photographie de paysage, The Tetons and the Snake River d'Ansel Adams (1942).|193x193px thumb|redresse|Raising the Flag on Iwo Jima, par Joe Rosenthal. La photographie est un art visuel, qui consiste à enregistrer un sujet en image fixe, avec un ensemble de techniques, de procédés et de matériels. Par extension, le terme «photographie» désigne aussi le c'est-à-dire . Étymologie Le substantif féminin « photographie » (photography) a été proposé par John Herschel dès et provient de deux racines d'origine grecque :

le préfixe « photo- » (φωτoς, photos : lumière, clarté) — « qui procède de la lumière », « qui utilise la lumière » ;
le suffixe « -graphie » (γραφειν, graphein : peindre, dessiner, écrire) — « qui écrit », « qui aboutit à une image ».

« Photographie » signifie ainsi litté

Sampling Geometry and Colour

Michalina Wanda Pacholska

In this thesis, we take a signal-processing approach to two research areas outside of the core of the signal processing research: geometry reconstruction and light propagation through non-uniform media.In the first area, we consider new sampling schemes inspired by problems of surface recovery and continuous localisation. We analyse sampling at unknown locations and show signal recovery uniqueness under constraints. We also study non-synchronised sampling of vector-valued signals or fields, that arise in the problem of localisation of a smoothly moving device. We provide sufficient conditions for device localisation. To this end, we formulate the problem of rank-one sensing of full-rank matrices and develop sufficient conditions for matrix recovery when some measurements are missing.In the second area, we study Lippmann photography, a century-old colour photography technique. We model recording and viewing of a Lippmann photograph as analysis and synthesis operators and study the invertibility of their composition. We extend our analysis to a potential method of creating digital photographs, namely internal modification of glass with femto-second lasers.

EPFL2021

Quanta burst photography

Claudio Bruschini, Edoardo Charbon, Shantanu Gupta, Mohit Gupta, Arin Can Ülkü

Single-photon avalanche diodes (SPADs) are an emerging sensor technology capable of detecting individual incident photons, and capturing their time-of-arrival with high timing precision. While these sensors were limited to singlepixel or low-resolution devices in the past, recently, large (up to 1 MPixel) SPAD arrays have been developed. These single-photon cameras (SPCs) are capable of capturing high-speed sequences of binary single-photon images with no read noise. We present quanta burst photography, a computational photography technique that leverages SPCs as passive imaging devices for photography in challenging conditions, including ultra low-light and fast motion. Inspired by recent success of conventional burst photography, we design algorithms that align and merge binary sequences captured by SPCs into intensity images with minimal motion blur and artifacts, high signal-to-noise ratio (SNR), and high dynamic range. We theoretically analyze the SNR and dynamic range of quanta burst photography, and identify the imaging regimes where it provides significant benefits. We demonstrate, via a recently developed SPAD array, that the proposed method is able to generate high-quality images for scenes with challenging lighting, complex geometries, high dynamic range and moving objects. With the ongoing development of SPAD arrays, we envision quanta burst photography finding applications in both consumer and scientific photography.

2020

Sampling the Multiple Facets of Light

Gilles Baechler

The theme of this thesis revolves around three important manifestations of light, namely its corpuscular, wave and electromagnetic nature. Our goal is to exploit these principles to analyze, design and build imaging modalities by developing new signal processing and algorithmic tools, based in particular on sampling and sparsity concepts. First, we introduce a new sampling scheme called variable pulse width, which is based on the finite rate of innovation (FRI) sampling paradigm. This new framework enables to sample and perfectly reconstruct weighted sums of Lorentzians; perfect reconstruction from sampled signals is guaranteed by a set of theorems. Second, we turn to the context of light and study its reflection, which is based on the corpuscular model of light. More precisely, we propose to use our FRI-based model to represent bidirectional reflectance distribution functions. We develop dedicated light domes to acquire reflectance functions and use the measurements obtained to demonstrate the usefulness and versatility of our model. In particular, we concentrate on the representation of specularities, which are sharp and bright components generated by the direct reflection of light on surfaces. Third, we explore the wave nature of light through Lippmann photography, a century-old photography technique that acquires the entire spectrum of visible light. This fascinating process captures interferences patterns created by the exposed scene inside the depth of a photosensitive plate. By illuminating the developed plate with a neutral light source, the reflected spectrum corresponds to that of the exposed scene. We propose a mathematical model which precisely explains the technique and demonstrate that the spectrum reproduction suffers from a number of distortions due to the finite depth of the plate and the choice of reflector. In addition to describing these artifacts, we describe an algorithm to invert them, essentially recovering the original spectrum of the exposed scene. Next, the wave nature of light is further generalized to the electromagnetic theory, which we invoke to leverage the concept of polarization of light. We also return to the topic of the representation of reflectance functions and focus this time on the separation of the specular component from the other reflections. We exploit the fact that the polarization of light is preserved in specular reflections and investigate camera designs with polarizing micro-filters with different orientations placed just in front of the camera sensor; the different polarizations of the filters create a mosaic image, from which we propose to extract the specular component. We apply our demosaicing method to several scenes and additionally demonstrate that our approach improves photometric stereo. Finally, we delve into the problem of retrieving the phase information of a sparse signal from the magnitude of its Fourier transform. We propose an algorithm that resolves the phase retrieval problem for sparse signals in three stages. Unlike traditional approaches that recover a discrete approximation of the underlying signal, our algorithm estimates the signal on a continuous domain, which makes it the first of its kind. The concluding chapter outlines several avenues for future research, like new optical devices such as displays and digital cameras, inspired by the topic of Lippmann photography.

EPFL2018

Sampling the Multiple Facets of Light

Gilles Baechler

EPFL2018