Optical-computing device and method for analysing light passing through a container made of transparent or translucent material by means of a digital polarimetric camera

An optical-computing method for analyzing, via transmitted light, a container made of transparent or translucent material, using a polarimetric camera, the polarimetric camera including a two-dimensional photoelectric sensor comprising photoelectric elements each comprising a photoelectric cell, wherein the photoelectric cell is arranged in front of a polarization analysis system comprising at least one individual polarization analyzer associated with the photoelectric cell of the photoelectric element, the photoelectric sensor comprising a number N of distinct groups of contiguous photoelectric elements, each distinct group of contiguous photoelectric elements comprising a number K greater than or equal to two of photoelectric elements belonging to one of a number F greater than or equal to two distinct families of photoelectric elements, respectively, each family of photoelectric elements being defined by a polarization analysis characteristic of the polarization analysis system common to each of the photoelectric elements thereof, the polarization analysis characteristics of at least two families comprising at least two linear analyses along two orthogonal axes of polarization or at least two circular analyses in opposite directions to each other, each distinct group of photoelectric elements comprising at least two photoelectric elements belonging to at least two distinct families, and each distinct group of contiguous photoelectric elements corresponding to a composite pixel in a master image delivered by the sensor, the method including:

• illumination of the container from the rear by an illumination device delivering, onto the container, incident light, polarized either circularly with a first direction of rotation, or linearly along an incidence axis of polarization;
• observation of the container, from the front, by the polarimetric camera, so as to collect, on the photoelectric sensor of the polarimetric camera, an emerging light coming from the container;
• acquisition, with the photoelectric sensor of the polarimetric camera, of at least one digital master image of the container, having a number K*N of master pixels corresponding to N distinct groups of contiguous photoelectric elements, the master image comprising N composite pixels, each composite pixel corresponding to one of the groups of contiguous photoelectric elements, and the master image comprising the number K of distinct partial images each having N partial pixels, the partial pixels of each partial image corresponding, for a given partial image, to only one family of photoelectric elements of the photoelectric sensor taken from the N composite pixels;
• computation of an intensity image wherein the value of each intensity pixel is an averaged value of the value of at least two partial pixels corresponding to two photoelectric elements of the same group but belonging to two distinct families of photoelectric elements the polarization analysis characteristics of which are two circular analyses of opposite directions to each other or two linear analyses of orthogonal axes of polarization or two orthogonal elliptical analyses;
• computation of at least one phase shift image by calculating, for a series of composite pixels, a phase shift pixel which corresponds to a composite pixel and the value of which is representative of an polarization phase shift, induced by a residual mechanical stress in the elementary zone of the container corresponding to the composite pixel, in the light emerging from the elementary zone of the container corresponding to the composite pixel, from the value of a set of one or a plurality of partial pixels all extracted from the composite pixel and belonging to a combination of one or a plurality of partial images, the computation of each phase shift pixel of a given phase shift image being carried out from the same combination of one or a plurality of partial images.