Method for inspecting the side wall of an object

An apparatus for inspecting a side wall of an object, wherein the side wall of the object extends round a respective axis, the apparatus comprising:

• a conveyor configured to transport the object;
• an inspection station, disposed along the conveyor and configured to receive the object to be inspected oriented with the respective axis of the object along a longitudinal direction;
• wherein the inspection station comprises an optical device for capturing images;
• wherein the optical device comprises a first camera, configured to capture a first image of the object from above, wherein the first camera has an optical path which has at least one component that is parallel to the longitudinal direction,
• wherein the optical device is configured to capture a second image of the object, through the first camera or through a second camera, representing a portion of the side wall of the object to be inspected;
• a control unit, including a processor, configured for:
• deriving a three-dimensional representation of the side wall of the object based on the first image and on reference data;
• performing a step of processing the second image as a function of the three- dimensional representation, wherein the step of processing includes:
• identifying a first plurality of points on the three dimensional representation,
• identifying a second plurality of points on the second image,
• applying a correlation between the first plurality of points and the second plurality of points;
• deriving a third image, the third image being obtained by perspective transformation of the second image, based on the three-dimensional representation representing the portion of the side wall of the object, the third image being without perspective distortion or being less distorted than the second image;
• making the third image available to identify defects in the portion of the side wall of the object,
• wherein the reference data include a distance of an upper outer edge of a lateral surface of the object from the first camera and
• wherein the control unit is configured to identify, on the first image, a line representing at least one portion of the upper outer edge of the lateral surface of the object and to derive the three-dimensional representation from the line, and
• wherein the reference data also include a height of the side wall of the object, wherein the control unit is configured to derive the three-dimensional representation by projecting the line downwardly for a height equal to the height of the side wall of the object.

A method for processing an image of a side wall of an object, wherein the image has perspective distortion, the method comprising the following steps:

• deriving, by means of a control unit, which includes a processor, a three-dimensional representation of the side wall of the object based on a first image, captured through a first camera, of the object viewed from above and on reference data;
• identifying, by means of the control unit, a first plurality of points on the three-dimensional rep resentation;
• identifying, by means of the control unit, a second plurality of points on a second image representing a portion of the side wall of the object, captured through a first camera or a second camera;
• applying, by means of the control unit, a correlation between the first plurality of points and the second plurality of points;
• deriving, by means of the control unit, a further image, the further image being obtained by perspective transformation of the second image, based on the three-dimensional representation, representing a portion of the side wall of the object, the further image being without perspective distortion or being less distorted than the second image,
• wherein the step of deriving the three-dimensional representation includes identifying, on the first image, a line representing at least one portion of an upper outer edge of a lateral surface of the object, and
• wherein the reference data include a distance of an upper outer edge of the lateral surface of the object from the first camera, and
• wherein the reference data also include a height of the side wall of the object, wherein the three-dimensional representation is derived from the line by projecting the line along the longitudinal direction for a height equal to the height of the side wall of the object.