Method for determining elements in relief on the surface of a tyre

A method of extracting, from an image, relief elements featured on a surface of a tyre, the method comprising steps of:

• assigning, to each pixel (i, j) of a three-dimensional image of the surface, a grey-level value proportional to a topographic elevation of a point corresponding to the pixel, so as to obtain a starting image (ƒ);
• using a structuring element to transform the starting image (ƒ) by a first top-hat operation, so as to obtain an image (ƒ1) flattened by differencing, (ƒ1=ƒ—γ3,151(ƒ));
• using first and second structuring elements to transform the image flattened by differencing (ƒ1) by a second top-hat with filtering operation, so as to obtain a filtered image acting as marker (ƒ2=FTH (ƒ1)=ƒ1—((γ31,151(φ31,51(ƒ1))) ƒ1))
• reconstructing the image flattened by differencing based on markers contained in the filtered image, so as to form a reconstructed filtered image (ƒ3=Rδƒ1(ƒ2);
• using structuring elements of given sizes, shapes, and orientations to transform the reconstructed filtered image successively by a series of top-hat with filtering operations, so as to obtain a series of filtered flattened images (ƒ4=FTH (ƒ3), ƒ5=FTH (ƒ4), ƒ6=FTH (ƒ5));
• and
• performing a thresholding operation on a last image (ƒ6) of the series of filtered flattened images, so as to obtain a segmented image (T<1,30>(ƒ6)=seg1) in which relief elements of a first color appear on a background of a second color.