1. A method for characterizing a perception of blur by a subject, comprising: /1/ selecting a blur perception criterion allowing a blur limit to be established on the basis of which the criterion is met or not for the subject; /2/ generating and displaying an image on a display screen, said image having a blur corresponding to a low-pass filtering of image components with respect to space frequencies of said image components; /3/ receiving from the subject, said subject being free to move further from or nearer to the display screen thereby varying a distance of observation, a report of whether the blur perception criterion selected in step /1/ is met or not when the subject observes the displayed image; /4/ selecting a value for the distance of observation achieved by the subject during step /3/; /5/ determining, from the value selected in step /4/ for the distance of observation and from a cut-off spatial frequency of the low-pass filtering of the displayed image, a dioptric blur value for the displayed image observed by the subject, said dioptric blur value being associated with the report received from the subject in step /3/ for responding to the perception of blur criterion, and said dioptric blur value being a decreasing function of the value selected for the distance of observation when a cut-off spatial frequency of the low-pass filtering of the displayed image is constant.