1. Field of the Invention
The present invention relates to a process for regulating the exposure time of a light sensor. More particularly, the invention relates to a process for regulating the exposure time of a light sensor according to the variation of luminosity in the work environment in which the sensor is located.
2. Discussion of the Prior Art
Throughout the present description and the attached claims, with the term: “light sensor”, it is intended to indicate a light-sensitive optical element capable of converting a light signal, contained in a incident light beam, in an analogic electrical signal proportional to the light intensity of the light itself. In particular, the light sensor transforms the light image of an illuminated object into an electronic image thereof, in order to allow the carrying out of further operations of image processing, such as for example those connected to the reading of an optical code located on the object.
In the following, reference to light sensors of known type will be made, for example CCD or CMOS sensors, both linear and of matrix type.
As is known, a drawback associated with light sensors at present available on the market is correlated to the fact that their operation is strongly influenced by the variations in luminosity of the surface on which the image to be acquired is to be found (such surface can be more or less clear and more or less illuminated). In particular, the resolution of the image acquired by the sensor (that is the richness of details detected in the image acquired by it) considerably varies according to the variation of the luminosity of the surrounding environment and of the surface to be acquired: highly illuminated environments can as such create conditions of strong overexposure or saturation (little contrast) of the image on the sensor, whilst badly illuminated environments can create conditions of strong under-exposure (excessive dark) in the image on the sensor. In both cases, the image acquired by the sensor appears badly exposed and not very clear, therefore making it impossible to detect details having small sizes.
In particular, with reference to the reading of an optical code, the acquisition on the sensor of an image of an optical code having a low resolution is often undesired because it renders the subsequent operations of localization, reading and decoding of the code itself very approximate and rough; this is absolutely unacceptable where it is necessary to carry out a correct decoding of the code in order to unequivocally identify the object having the code thereon.
The drawbacks associated with the acquisition of an image having low resolution can be overcome by suitably regulating the exposure time of the sensor according to the variations of luminosity of the surrounding work environment and of the surface to be acquired. In particular, where an increase in luminosity occurs in the work environment, it would be advisable to set a shorter exposure time on the sensor, in order to avoid the risk of generating conditions of saturation of the acquired image; viceversa, in the case where a decrease in luminosity occurs in the work environment, it would be advisable to set a higher exposure time on the sensor, in order to avoid the risk of generating conditions of under-exposure of the acquired image.
The majority of light sensors at present available on the market allow to set an exposure time by choosing it between a range of values, more or less extensive, each differing the one from the other by descrete amounts; such values are stated by the manufacturers of the sensors.