Publications by authors named "Stephane Roussel"

A linear division-of-focal-plane camera combined with a controllable polarization modulator constitutes a versatile full-Stokes imager with four possible sampling rate modes, depending on the number of acquisitions. Considering several polarization modulator architectures, we determine the parameter settings that minimize estimation variance in each sampling rate mode, so that precision, sampling rate, and acquisition time can be optimally and dynamically balanced to implement the imaging solution best adapted to a given application.

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We investigate the validity domain and precision of retardance autocalibration in full-Stokes imaging polarimeters based on a linear division-of-focal-plane polarization camera. We demonstrate that the level of precision of autocalibration in these systems gets worse as the degree of linear polarization of input Stokes vector approaches zero. Autocalibration is impossible when the input is purely circular or totally unpolarized.

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Polarimetric cameras based on micropolarizer grids make it possible to design division of focal plane (DoFP) polarimeters. However, the polarimetric estimation precision reached by these devices depends on their realization quality, which is estimated by calibration. We derive the theoretical expressions of the estimation variance of such polarimetric parameters as an angle of linear polarization and degree of linear polarization as a function of the calibrated micropolarizer characteristics.

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We investigate the target detection performance of static Mueller imagers that implement a fixed number of illumination and analysis polarization states. Using a maximin approach, we demonstrate that the optimal sets of measurement vectors consist in regular tetrahedra on the Poincaré sphere and that, in this case, the obtained target/background contrast has a very simple expression. We then derive a universal lower bound on the contrast ratio between the best channel of a static imager and a fully adaptive one, and in a special case of practical interest, we demonstrate that this ratio is bounded and always larger than 1/9.

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Mueller polarimetric imaging enables the detection and quantification of modifications of the collagen fibers in the uterine cervix due to the development of a precancerous lesion. This information is not accessible through the use of the classic colposcope, a low magnification microscope used in current practice for cervical cancer screening. However, the in vivo application of Mueller polarimetric imaging poses an instrumental challenge: the device should be sufficiently compact, while still being able to perform fast and accurate acquisition of Mueller matrices in real-world conditions.

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This report describes how optical images acquired using linearly polarized light can specify the anisotropy of scattering (g) and the ratio of reduced scattering [μs′=μs(1−g)] to absorption (μa), i.e., N′=μs′/μa.

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