An optical-computing method for analyzing, via transmitted light, a container made of transparent or translucent material having a rear and a front, using a polarimetric camera, the polarimetric camera including a two-dimensional photoelectric sensor comprising photoelectric elements each comprising a photoelectric cell, wherein each of the photoelectric cells 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 N distinct groups of contiguous photoelectric elements;
- each distinct group of contiguous photoelectric elements comprising K photoelectric elements, wherein K is greater than or equal to two, and wherein the photoelectric elements belong to F distinct families of photoelectric elements, wherein F is greater than or equal to two;
- wherein each family of photoelectric elements is 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 photoelectric sensor;
- the optical computing method comprises:
- illuminating the container from the rear by an illumination device having at least two dimensions delivering, onto the container, incident light that is polarized either circularly with a first direction of rotation, or linearly along an incidence axis of polarization;
- observing the container, from the front, by the polarimetric camera, so as to collect, on the photoelectric sensor of the polarimetric camera, an emerging light emitting from a point of the container;
- acquiring, with the photoelectric sensor of the polarimetric camera, at least one digital master image of the container, having K*N 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 K distinct partial images each having N partial pixels, of which each partial pixel has a value proportional to the intensity of the emerging light emitted by the point of the container, 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;
- computing an intensity image, comprising at least one intensity pixel each having a value, 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;
- computing at least one phase shift image each having at least one phase shift pixel by calculating, for a series of composite pixels, a phase shift pixel value which is representative of a polarization phase shift, induced by a residual mechanical stress in an elementary zone of the container, the elementary zone being a location on 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 at least one partial pixel all extracted from the composite pixel and belonging to a combination of at least one partial image(s), wherein the value of each phase shift pixel of a phase shift image is calculated from the same combination of the at least one partial image(s).