Optical computing methods and systems for inspecting a glass container in transmitted light

An optical computing method for inspecting in through light a glass container moving along a movement trajectory, wherein:

• the method includes illumination of the container by an illumination device comprising at least one two-dimensional emitting surface which is arranged on one side of the movement trajectory and which is made up of elementary emitting areas each emitting a polarized emitted light with an emitted polarization property of interest which varies according to a law of periodic variation as a function of a position of the elementary emitting area in the emitting surface;
• the method includes an observation of the container, by at least one digital camera having a two-dimensional photoelectric sensor comprising photoelectric elements which each comprise a photoelectric cell corresponding to a pixel in an image acquired by the digital camera, the at least one digital camera being located, with respect to the movement trajectory, on a side opposite to that of the illumination device, so as to collect, by the at least one digital camera, an emergent light emanating from the container and having crossed at least one wall thickness of the container;
• the method includes the acquistion, with the at least one digital camera, of partial digital images, each containing an image of the same inspected area of the container, each partial digital image having N partial pixels each of which is the image of a corresponding elementary area of the container, and each partial digital image being acquired with interposition, between the container and the photoelectric cells of the at least one digital camera, of a linear analyzer having a given axis of polarization, for a partial digital image;
• the acquisition further includes another acquisition of at least one series comprising at least a first partial digital image and a second partial digital image, for which the axes of polarization of the linear analyzers are distinct from each other, the partial digital images of the same series being superimposable such that each elementary area of the inspected area of the container is imaged by a corresponding partial pixel in each of the partial digital images of the series;
• for a primary series, the partial digital images of the primary series each contain, in the background, the image of the same primary inspection portion of the emitting surface, the primary inspection portion being observed through the container by the digital camera, and, on the primary inspection portion of the emitting surface, the law of periodic variation of the emitted polarization property of interest having, along a primary direction, a primary periodic variation, and having several primary periods over the extent of the primary inspection portion along the primary direction;
• wherein, over a primary period, the emitted polarization property of interest of the lights emitted by the elementary emitting areas of the primary inspection portion of the emitting surface follows a triangular variation as a function of the position of the elementary emitting area along the primary direction,
• and in that the method includes a computer calculation of at least one primary raw refraction image, from the partial digital images of the primary series, by calculating, for each of the elementary areas of an inspected area of the container, a primary raw refraction pixel whose value is representative of the refraction undergone by the light having crossed at least one wall thickness of the container and emerging from the elementary area, from the value of the corresponding partial pixels which are the image of the elementary area in the partial digital images of the primary series.