A method for determining wavefront shapes of a multi-spectral signal light beam from a single signal image acquisition of said multi-spectral signal beam, with a device including an optical assembly made at least of an optical mask and an imaging sensor, notably a matrix imaging sensor, for generating and recording intensity patterns of incident beams, by having these beams reflect on, or propagate through, the optical mask. The optical mask having the optical properties: i) to cause the intensity pattern to depend on the wavefront shape, so that a tilt applied to the wavefront shape results in a displacement amount of the intensity pattern, and ii) to produce uncorrelated intensity patterns over at least one surface area A of the imaging sensor, for a plurality of respective incident monochrome beams of different wavelengths having a same wavefront shape.