RU-2861360-C2 - OPTICAL COMPUTING DEVICE AND METHOD FOR TRANSMITTED LIGHT ANALYSIS OF CONTAINER MADE OF TRANSPARENT OR TRANSLUCENT MATERIAL BY MEANS OF DIGITAL POLARIMETRIC CAMERA

RU2861360C2RU 2861360 C2RU2861360 C2RU 2861360C2RU-2861360-C2

Abstract

FIELD: optical computing device. SUBSTANCE: present invention relates to an optical computing device and a method for analysing a container (12) made of a transparent or translucent material using a polarimetric camera (18), wherein the method comprises steps of: obtaining at least one reference digital image (IM) of the container using a photoelectric sensor (22) of the polarimetric camera; calculating an intensity image (It), in which the value of each pixel (Pt(n)) of intensity is an average value of the values of at least two pixels of the reference digital image corresponding to two circular analyses in opposite directions, or two linear analyses with orthogonal polarisation axes, or two orthogonal elliptical analyses; calculating at least one phase shift image (ID) by calculating, for a series of composite pixels, a phase shift pixel (Pd(n)) based on the values of a set of one or more partial pixels (Ppk(n)) belonging to a combination of one or more partial images (Ipk). EFFECT: simplifying the design while providing information used to limit the risk of unnecessary rejection of containers. 18 cl, 12 dwg

Inventors

DRUETTO, Raphael
LECONTE, MARC
PENSEC, Yann

Dates

Publication Date: 20260505
Application Date: 20221006
Priority Date: 20211008

Claims (20)

1. An optical-computational method for analyzing in transmitted light a container (12) made of a transparent or translucent material, such as glass, using a polarimetric camera (18), wherein the polarimetric camera includes a two-dimensional photoelectric sensor (22) containing photoelectric elements (26(f,n,k)), each of which contains a photoelectric cell (28(f,n,k)), in front of which a polarization analysis system is placed, containing at least one individual polarization analyzer (30(f,n,k)) associated with a photoelectric cell of the photoelectric element,
wherein the photoelectric sensor comprises N different groups (26(n)) of adjacent photoelectric elements, wherein each of the different groups of adjacent photoelectric elements comprises K, where K is greater than or equal to two, photoelectric elements (26(f,n,k)) belonging respectively to one of F, where F is greater than or equal to two, different families of photoelectric elements (26(f,n,k)), wherein each family of photoelectric elements is determined by a polarization analysis characteristic of a polarization analysis system common to each of its photoelectric elements (26(f,n,k)), wherein the polarization analysis characteristics of at least two families comprise at least two linear analyzes along two orthogonal polarization axes or at least two circular analyzes in directions opposite to each other, wherein each of the different groups (26(n)) of photoelectric elements comprises at least two photoelectric elements (26(f,n,k)) belonging to at least two different families, and each of the different groups of adjacent photoelectric elements corresponds to a composite pixel (Pc(n)) on the reference image (IM) transmitted by the sensor, wherein the method includes the steps of:
the container is illuminated from behind using a lighting device (16) that supplies incident light to the container, polarized either circularly in the first direction of rotation or linearly along the polarization axis of the incident light;
observe the container (12) from the front with a polarimetric camera (18) for collecting, a photoelectric sensor (22) of the polarimetric camera, the output light coming from the container;
at least one digital reference image (IM) of a container having K*N reference pixels (Pm(f,n,k)) corresponding to N different groups of adjacent photoelectric elements is obtained by the photoelectric sensor (22) of the polarimetric camera, wherein the reference image contains N composite pixels (Pc(n)), wherein each composite pixel corresponds to one of the groups (26(n)) of adjacent photoelectric elements, and the reference image (IM) contains K different partial images (IPk), each of which has N partial pixels (Ppk(n)), wherein the partial pixels (Ppk(n)) of each partial image correspond, for a given partial image (Ipk), to only one family of photoelectric elements of the photoelectric sensor (22), taken from the N composite pixels (Pc(n));
an intensity image (It) is calculated in which the value of each intensity pixel (Pt(n)) is an average value of the values of at least two partial pixels (Ppk(n)) corresponding to two photovoltaic elements of the same group (26(n)), but belonging to two different families of photovoltaic elements (26(f,n,k)), the polarization analysis characteristics of which are two circular analyses in opposite directions, or two linear analyses of orthogonal polarization axes, or two orthogonal elliptical analyses;
at least one phase shift image (ID) is calculated by calculating, for a series of composite pixels, a phase shift pixel (Pd(n)) which corresponds to a composite pixel (Pc(n)) and the value of which represents a phase shift (ϕ(n)) of polarization caused by residual mechanical stress in an elementary zone of the container (12) corresponding to the composite pixel (Pc(n)), in light emerging from the elementary zone of the container corresponding to the composite pixel (Pc(n)), based on the value of a set of one or a plurality of partial pixels (Ppk(n)), each of which is extracted from the composite pixel (Pc(n)) and belongs to a combination of one or a plurality of partial images (IPk), wherein the calculation of each phase shift pixel (Pd(n)) of a given phase shift image (ID) is performed based on the same combination of one or a plurality of partial images (IPk).
2. An optical-computational method of analysis according to paragraph 1, in which:
the photoelectric sensor (22) comprises at least two different families of photoelectric elements (26(f,n,k)), the polarization analysis characteristics of which are two linear analyses respectively along the first polarization axis and the second polarization axis orthogonal to the first polarization axis;
the incident light is linearly polarized along the second polarization axis;
the calculation of each pixel (Pd(n)) of the phase shift of the given phase shift image is performed on the basis of the value of at least a partial pixel (Ppk(n)) corresponding to the first polarization axis;
the value of each intensity pixel of the intensity image is an average value of the values of two partial pixels extracted from the same composite pixel, each of which is associated with one of two families whose polarization axes are orthogonal, and/or two partial pixels, each of which is associated with one of two different families of photovoltaic elements whose polarization analysis characteristics are two circular analyses in opposite directions.
3. An optical-computational analysis method according to paragraph 1, in which:
the photoelectric sensor (22) contains at least four different families of photoelectric elements (26(f,n,k)), the polarization analysis characteristics of which contain at least four linear analyzes along polarization axes containing two pairs ((A1, A3), (A2, A4)) of orthogonal polarization axes, wherein said two pairs of polarization axes are shifted relative to each other by an angle of 45 degrees;
the incident light is circularly polarized in the direction of incidence;
the calculation of each phase shift pixel (Pd(n)) for a given phase shift image is performed on the basis of the values of four partial pixels (Ppk(n)) extracted from the same composite pixel (Pc(n)), each of which is associated with one of four different families of photovoltaic elements whose polarization analysis characteristics are the said linear analyses;
the value of each pixel (Pt(n)) of the intensity image (It) intensity is an average value of the values of at least two partial pixels (Ppk(n)) extracted from the same composite pixel (Pc(n)), each of which is associated with two different families of photovoltaic elements, the polarization analysis characteristics of which are two linear analyses of orthogonal polarization axes.
4. An optical-computational method of analysis according to paragraph 1, in which:
the incident light is circularly polarized in one direction of incidence;
the photoelectric sensor (22) comprises at least one family of photoelectric elements (26(f,n,k)), the polarization analysis characteristic of which is a circular analysis in the direction opposite to the direction of incidence;

Description

Field of technology to which the invention relates The present invention relates to an optical-computational method for analyzing a glass container in transmitted light using a digital polarimetric camera, which makes it possible, in particular, to perform a computerized detection of defects, if any, in the container material, namely in a transparent or translucent material, in order to be able to determine whether such defects are unacceptable. Throughout the description, transparent or translucent material refers to clear glass, in particular clear or colored glass, or plastics or polymers of any origin, such as polyethylene terephthalate (PET) or high-density polyethylene (HDPE). State of the art There are a large number of optical-computational methods for analyzing a glass container to detect defects therein using one or multiple digital cameras. The detection and, if necessary, identification or classification of defects is performed by computer analysis of one or multiple digital images obtained by the cameras. Some methods produce a digital image using light reflected from the container. Other methods, such as those provided in the present invention, operate using transmitted light, with the light source then being within the field of view of the digital camera used. In the most traditional methods, any defects are detected in one or multiple digital intensity images obtained by the camera using computational methods. Anomalies in the image arise from the complete or partial absorption or refraction by the defect of the incident light projected by the light source. Thus, the digital image used for such analysis is a digital intensity image, each pixel of which has a value proportional to the intensity of light emitted by a point on the container optically corresponding to a pixel in the camera's optical system. Such detection on a digital intensity image serves, as a rule, to determine the location of defects in the container and, if necessary, to determine the size and shape of said defects, provided, however, that the defect results in an anomaly in the absorption or refraction of light with respect to the container material surrounding the defect. Among the optical-computational methods that operate in transmitted light, there are also methods that determine the presence of residual mechanical stress in a material by detecting the change in the polarization state of light after passing through the container material and through any defects in the material due to mechanical stress. Polarimetric cameras are currently available for implementing these methods. In particular, polarimetric chambers are known in which the polarimetric chamber includes a two-dimensional photoelectric sensor containing photoelectric elements, each of which contains a photoelectric element, in front of which a polarization analysis system is located, which will be hereinafter referred to as a polarization analyzer or simply an analyzer. The polarization analysis system contains a linear polarization filter, hereinafter referred to as an individual linear polarization analyzer or simply an individual linear analyzer, associated with each photocell of the photoelectric element. The photoelectric sensor includes a number N of different groups of adjacent photoelectric elements, wherein each of the different groups of adjacent photoelectric elements contains four adjacent photoelectric elements belonging to four different families of photoelectric elements, respectively. Each family of photoelectric elements is defined by the orientation of the polarization axis of its individual linear polarization analyzer, wherein the orientation of the polarization axis of an individual linear polarization analyzer is common to each of the photoelectric elements of the family. In known polarimetric chambers, four linear analyses correspond to four orientations of the corresponding polarization axis and correspond to two pairs of orthogonal polarization axes, the two pairs being offset relative to each other by an angle of 45 degrees, in one direction or the other. For example, the XCG-CP series polarimetric cameras sold by SONY Group companies operate on this principle. The same SONY Group companies also sell two-dimensional photoelectric sensors that include a system of individual linear polarizing filters, each of which is connected to a photoelectric cell in accordance with the aforementioned principle. The sensors, known under the designations IMX250MZR/MYR, IMX253MAR/MYR, or IMX264MZR/MYR, manufactured using CMOS technology, contain individual linear polarizing filters formed directly on the component. The invention will be described in more detail below using an embodiment using such a camera. Another manufacturer of cameras that can be implemented in the case of the invention is Lucid Vision Labs, Inc., 130-13200 Delf Place, Richmond BC, Canada, V6V 2A2. Polarimetric sensors are also described in document EP 2275790. A device and op