1. A method for a real-time calculation of a number of signals to be summed from among a set of signals representative of an image portion which are respectively received from a set of detectors belonging to a same optical sensor, the set of detectors being organized in a matrix formed by rows and columns, said number of signals to be summed being received on a same column, and for a determination of a time during which the set of detectors must acquire said number of signals to be summed, the method comprising: (a) a step of determining a representative value representative of an image portion modulation transfer function and a signal-to-noise ratio, based on a location of one of the set of detectors and based on a signal representative of the image portion obtained from the set of detectors, said representative value depending on the number of signals, (b) a step of calculating for the number of signals and for the time maximizing said representative value, and, steps (a) and (b) being followed by: (c) a step of acquiring said number of signals to be summed on the same column.