1. 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 (ƒ 1 ) flattened by differencing, (ƒ 1 =ƒ—γ 3,151 (ƒ)); using first and second structuring elements to transform the image flattened by differencing (ƒ 1 ) by a second top-hat with filtering operation, so as to obtain a filtered image acting as marker (ƒ 2 =FTH (ƒ 1 )=ƒ 1 —((γ 31,151 (φ 31,51 (ƒ 1 ))) ƒ 1 )) reconstructing the image flattened by differencing based on markers contained in the filtered image, so as to form a reconstructed filtered image (ƒ 3 =R δ ƒ1 (ƒ 2 ); 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 (ƒ 4 =FTH (ƒ 3 ), ƒ 5 =FTH (ƒ 4 ), ƒ 6 =FTH (ƒ 5 )); and performing a thresholding operation on a last image (ƒ 6 ) of the series of filtered flattened images, so as to obtain a segmented image (T <1,30> (ƒ 6 )=seg 1 ) in which relief elements of a first color appear on a background of a second color.