A digital collimation technique based on the self-imaging phenomenon is proposed. Basically, a moiré pattern is observed by viewing the Fresnel image of an original self-imaged grating through a second grating. Decollimation of the laser beam causes a variation in the self-image period. In our method, the moiré beating is produced through a digital subtraction operation of a replica of the original grating and the self-images provided by a decollimated beam. The variation of the moiré period is related to the amount of decollimation of the illuminating beam. Lenses of different focal lengths were used in the collimation procedure, as well as gratings with different periods. The validity of the approach is experimentally demonstrated and setting sensitivities are compared.