A photographic sensor is a photosensitive electronic component used to convert electromagnetic radiation (UV, visible or IR) into an analog electrical signal. This signal is then amplified, then digitized by an analog-to-digital converter and finally processed to obtain a digital image.
The sensor is therefore the basic component of cameras and digital cameras, the equivalent of film (or foil) in silver photography.
The photographic sensor takes advantage of the photoelectric effect, which allows incident photons to extract electrons from each active element (photosite) of a matrix of elementary sensors consisting of photodiodes or photomos. It is much more efficient than the film: up to 99% (in theory) and nearly 50% (in practice) of the photons received can collect an electron, against about 5% of photons that reveal the photosensitive grain of the film, hence its initial development in astrophotography.
Two main families of sensors are available: CCD and CMOS.
CCDs still exist in the compact and very high resolution markets. The most common reflex cameras have abandoned it and use mainly CMOS sensors.
The CCD is the simplest to manufacture. Invented by George E. Smith and Willard Boyle at Bell Laboratories in 1969 (this invention earned them half of the Nobel Prize in Physics in 2009), it was quickly adopted for advanced applications (astronomical imaging) and then popularized for cameras and still cameras.
A CMOS (“complementary metal-oxide-semiconductor”) sensor is composed of photodiodes, like a CCD, where each photosite has its own charge-to-voltage converter and amplifier (in the case of an APS sensor).
Their power consumption, much lower than that of CCD sensors, their reading speed and the lower production cost are the main reasons for their wide use.
In the same way as many CCD, the CMOS sensors for color image are associated with a color filter and a lens array, even more necessary considering the small relative surface of the photodiode, the only sensitive area.
CCD sensors collect light better than their CMOS counterparts. The CCD has a system of reading line by line (full frame for example), which generally makes it more precise than the CMOS. Only 75% of the components present on the CMOS sensor are used to collect the light. That is to say that 25% of the sensor is made of electronic components which do not collect the light, but on the CMOS sensors the information is read with an indexing while the CCD does it line by line which improves the process of creation of the image!
CMOS is the most widespread, but that does not mean that it is the best, at the level of quality the CCD is above. As for speed, CMOS takes the lead, in addition to its low production cost (compared to CCD) and its low energy consumption! All these criteria have led manufacturers to gradually abandon the CCD type sensor in favor of the other, which can be seen with digital cameras.