Method of fast analysis of the relief elements featuring on the internal surface of a tyre
In a method of fast analysis of relief elements featuring on an inner surface of a tire, a three-dimensional image of the surface is captured, and each pixel of the image is assigned a greyscale value proportional to a topographical elevation of a point corresponding to the pixel, so as to obtain a starting image. The image is transformed into an orthogonal reference frame (OXY) in which an abscissa axis (OX) represents circumferential values and an ordinate axis (OY) represents radial values. Each point of the surface, i.e., each pixel, is assigned an altitude gradient value (f(p)) by comparing an elevation of the point with an elevation of a discrete and reduced number of points arranged on a straight line passing through a pixel being considered (p) and oriented in a circumferential direction.
1. A method of fast analysis of relief elements on an internal surface of a tyre, the method comprising steps of:
capturing a three-dimensional image of the internal surface of the tyre, each pixel (p(i,j)) of a plurality of pixels of the captured image corresponding to a topographical elevation of a point of the tyre;
assigning to each pixel of the plurality of pixels of the captured image a greyscale value (g(p)) proportional to the topographical elevation of a corresponding point of the tyre, so as to obtain a starting image;
transforming the starting image into an orthogonal reference frame (OXY) in which an abscissa axis (OX) represents a circumferential direction and an ordinate axis (OY) represents a radial direction;
assigning to each pixel (p(x,y)) of a plurality of pixels of the transformed image an altitude gradient value (f(p)) by comparing an elevation of a point corresponding to a pixel being considered (p) with elevations of a number of points arranged on a straight line passing through the pixel being considered and oriented in the circumferential direction, wherein the number of points is between 1 and 4.
2. The method of fast analysis according to claim 1 , further comprising a step of, after the step of assigning an altitude gradient value to each pixel, assigning a gradient value of zero to each pixel for which an altitude gradient value (f(p)) has an absolute value below a given threshold.
3. The method of fast analysis according to claim 2 , wherein, during the step of assigning an altitude gradient value to each pixel, an altitude gradient value (f(p x,y )=|g(x,y)−g(x+a,y)|) is assessed using a single point distant from a point corresponding to a pixel being considered (p(x,y)) by a given value (a).
4. The method of fast analysis according to claim 3 , wherein the internal surface includes striations, and wherein the single point is distant from the point corresponding to the pixel being considered by a length having the given value (a), which corresponds substantially to a circumferential spacing or width between two striations.
5. The method of fast analysis according to claim 2 , wherein, during the step of assigning an altitude gradient value to each pixel, an altitude gradient value
( f ( p x,y )=| g ( x,y )− g ( x+b,y )|− g ( x+a,y )− g ( x+a+b,y ),
f ( p x,y )=α(| g ( x−a,y )− g ( x−b,y )|+| g ( x+a,y )− g ( x+b,y )|)−β(| g ( x,y )− g ( x−b,y )|−| g ( x,y )− g ( x+b,y )|))
is assessed using four points positioned on one side of the pixel being considered and four points positioned on another side of the pixel being considered.
6. The method of fast analysis according to claim 5 ,
wherein the internal surface includes striations, and
wherein a value of (a) is between one and ten times a circumferential width of a striation, and a value of (b) is between one and five times the circumferential width of a striation.
7. The method of fast analysis according to claim 1 , further comprising a step of, after the step of assigning an altitude gradient value to each pixel, determining a reduced circumferential profile by assigning to a set of points located on a same circumferential abscissa, between two values of radial ordinates (y 1 ,y 2 ), a value (r(x)) representative of a variation of elevation of the points of the set.
8. The method of fast analysis according to claim 7 , wherein the reduced circumferential profile is determined by obtaining a sum or an average of absolute gradient values assigned to each of a group of pixels having a same radial position
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9. The method of fast analysis according to claim 7 , wherein the reduced circumferential profile (r(x)) is determined by counting a number of pixels situated on a same circumferential abscissa having a non-zero value.
10. The method of fast analysis according to claim 7 , wherein a signal representing the reduced circumferential profile (r(x)) is demodulated.
11. The method of fast analysis according to claim 10 , wherein the signal is demodulated by using a low-pass filter to subtract features from the reduced circumferential profile (r(x)), so as to show only elements having an amplitude above a threshold of the low-pass filter.
12. The method of fast analysis according to claim 10 , wherein the internal surface includes striations, and wherein the signal representing the reduced circumferential profile (r(x)) is demodulated by eliminating periodic elements.
13. The method of fast analysis according to claim 12 , wherein an infimum of the reduced circumferential profile (r(x)) is subtracted from the reduced circumferential profile with an offset from a value of a period of a circumferential appearance of striations
( m ( x )= r ( x )− ( r ( x ), r ( x−s )).