Image Recovery for Blind Polychromatic Ptychography

TL;DR

This paper introduces a novel approach for blind polychromatic ptychography, enabling the reconstruction of both the object and unknown light spectrum using an alternating minimization algorithm with guaranteed convergence.

Contribution

It extends ptychography to polychromatic light and develops an alternating minimization method for blind recovery with proven convergence guarantees.

Findings

Reformulates non-blind polychromatic ptychography as quadratic measurements recovery.

Proposes an alternating minimization algorithm for blind ptychography.

Proves sublinear convergence of the proposed method.

Abstract

Ptychography is a lensless imaging technique, which considers reconstruction from a set of far-field diffraction patterns obtained by illuminating small overlapping regions of the specimen. In many cases, a distribution of light inside the illuminated region is unknown and has to be estimated along with the object of interest. This problem is referred to as blind ptychography. While in ptychography the illumination is commonly assumed to have a point spectrum, in this paper we consider an alternative scenario with non-trivial light spectrum known as blind polychromatic ptychography. Firstly, we show that non-blind polychromatic ptychography can be seen as a recovery from quadratic measurements. Then, a reconstruction from such measurements can be performed by a variant of Amplitude Flow algorithm, which has guaranteed sublinear convergence to a critical point. Secondly, we address recovery from blind polychromatic ptychographic measurements by devising an alternating minimization version of Amplitude Flow and showing that it converges to a critical point at a sublinear rate. Keywords: ptychography, phase retrieval, blind, alternating minimization, gradient descent.