Method and apparatus for automatic optical recognition of road signs

A device for automatic recognition of an image, comprising:

• a modulator in which a first intensity spectrum of reference images and an image to be recognized has been pre-recorded;
• a laser beam source for directing the laser beam with an optical axis so as to pass through the modulator so as to generate a second intensity spectrum having peaks and spurious peaks, the peaks indicating that one of the reference images is identical to the image to be recognized;
• a converging lens placed downstream of the modulator and receiving the laser beam after the laser beam passes through the modulator;
• means for analyzing the second intensity spectrum occurring at the focal plane of the converging lens, including means for detecting and separating the peaks of the second spectrum indicating that a reference image is identical to the image to be recognized from the spurious peaks;
• and
• wherein the means for analyzing includes a mask for differentially polarizing portions of the beam containing the second intensity spectrum having the various peaks, and polarization separation optics placed downstream of the mask.

A process for automatic recognition of a road sign, comprising the steps of:

• displaying on a screen an input image containing the image of the sign to be recognized as well as images of reference signs;
• causing a first laser beam to pass through this screen and an initial lens in order to focus the first laser beam on a modulator capable of recording an intensity spectrum;
• illuminating the modulator with a second laser beam;
• causing said second laser beam to pass through a second lens as the second laser beam leaves the modulator in order to produce a second spectrum supplied to a detection system;
• determining whether the image of the sign to be recognized is identical to one of the images of reference signs based on the second spectrum;
• wherein the step of determining involves detecting correlation peaks of the various signs contained in the input image, within the focal plane of the second lens, in such a way that the presence of intensity peaks exceeding a predetermined threshold and offset with respect to the optical center of the image indicates that the image of the sign to be recognized is identical to one of the images of reference signs;
• and
• wherein the input image originates as a landscape image containing the sign to be recognized and undergoes a contour detection in order to adapt the input image to the input screen and decrease the spectral range.