Method of obtaining an image using an image sensor with a broad dynamic range

A method of obtaining an image using a broad dynamic range image sensor, made in CMOS type technology, including a photosensitive cell formed of a set of pixels, each pixel including a photodetector element for accumulating charge carriers as a function of the level of illumination thereof, a first initialization transistor series connected to the photodetector element between two supply terminals of a voltage source, storage means able to be coupled to said photodetector element via a second sampling transistor to store a voltage level representative of said charge carriers accumulated by said photodetector element, a third initialization transistor series connected to the storage means between the two supply terminals, and fourth and fifth series connected transistors, of which one control terminal of the fourth transistor is connected to the storage means for reading the voltage level stored in the storage means, wherein the method includes a series of steps of:

• a) controlling the conduction of the second and third transistors to impose a first initialization voltage on the terminals of the photodetector element and the storage means, the first transistor being in a non-conductive state;
• b) interrupting the conduction of the second transistor to start a first exposure period in which the photodetector element accumulates charge carriers as a function of the illumination level picked up;
• c) controlling the conduction of the first transistor to impose a second initialization voltage on the terminals of the photodetector element, the second initialization voltage being lower than the first initialization voltage, if the voltage level at the terminals of the photodetector element is less than the second initialization voltage at the end of the first exposure period;
• d) interrupting the conduction of the first transistor to start a second exposure period in which the photodetector element accumulates charge carriers;
• e) controlling the conduction of the second transistor after interrupting the conduction of the third transistor during the second exposure period to store the voltage level of the photodetector element in the storage means;
• and
• f) reading the voltage level stored in the storage means, when the second transistor is in a non-conductive state, by controlling the conduction of the fourth and fifth transistors.