Method for calculating information relative to a relative speed between an object and a camera, a control method for a vehicle, a computer program, a computer-readable recording medium, an object motion analysis system and a control system

An object motion analysis system, the object motion analysis system comprising a processor configured, based on an initial image (Ik) and a final image (Ik+1) of the object, derived from image frames outputted by a camera:

• to determine a value of an optical flow (F) between the initial image (Ik) and the final image (Ik+1), the optical flow defining, for pixels (x,y) of the initial image, an estimated motion (u,v) thereof during a transformation transforming the initial image (Ik) into the final image (Ik+1);
• and,
• altogether with or after the determination of the value the optical flow (u,v), to determine at least one parameter (s, tx, ty) of the transformation, using the optical flow;
• and
• to calculate information (RVD, TtC) relative to a relative speed between the object and the camera, based on said at least one parameter (s,tx,ty) of the transformation, wherein
• a transformed pixel being a pixel obtained by applying the transformation to a corresponding antecedent pixel,
• coordinates of a transformed pixel being therefore obtained by adding a value (u(x,y), v(x,y)) of the optical flow F for the corresponding antecedent pixel to coordinates (x, y) of the corresponding antecedent pixel;
• a first equation being an equation expressing the coordinates (x+u,y+v) of a transformed pixel as a function of the coordinates (x, y) of a corresponding antecedent pixel, using said at least one parameter (s, tx, ty) of the transformation;
• a second equation being an optical flow equation expressing, for a considered pixel (x, y), a relationship between spatio-temporal information
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• about pixel intensities at the considered pixel, spatio-temporal information
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• about pixel intensities I at another pixel which is offset from the considered pixel by an estimated offset value (ui, vi), and said at least one parameter (s,tx,ty) of the transformation;
• the processor is configured to execute an initial step of:
• determining initial values of said at least one parameter ((s,tx,ty)0) of the transformation and the optical flow (u0, v0);
• and
• the processor is configured to further iteratively execute steps of:
• determining updated values of said at least one parameter ((s,tx,ty)i+1) of the transformation, by solving a set of second equations established for considered pixels of the initial image, and based on an estimated value (ui, vi) of the optical flow F for said considered pixels;
• determining whether a new iteration has to be performed;
• and
• determining updated estimated values (ui+1, vi+1) of the optical flow F for said considered pixels, using a set of first equations for said considered pixels and the values of the at least one parameter of the transformation ((s, tx, ty)t+1).