Do you remember the old films of now obsolete cameras? It is amazing that in a few short years they are almost not to be found. Well, they were the sensitive element that recorded a fleeting view.

Now, after the digital revolution, solid state sensitive devices have no resemblance to the old film although they perform much the same function. These devices are called sensors or imagers.

Their delicate surface, divided into tiny picture elements or pixels, are made to accumulate charge (that is electrons) in proportion to the intensity of light (photons) coming through the camera lens and falling on each one of them.

The whole surface of the sensor is scanned according to a precise protocol, to collect information from each pixel in turn, about its color and brightness. Scanning produces an electrical signal as an analog streaming waveform, to be transmitted and used.

Competing technologies came up with different solutions (known as CMOS and CCD) each of which has its own set of advantages and limitations. They may differ in performance and cost but for general use both may produce acceptable pictures.

The struggle for supremacy is still continuing, and both devices are improving their quality and usability, gaining from the competition. The issue is too technical and charged with emotions and interests. The general public should not be involved, but only try to satisfy the requirement of their application, without taking parts.

The imager format, for surveillance cameras, may be a quarter of an inch, one third of an inch or half an inch. The larger the imager size, in principle, the higher the picture quality. But some small modern high density sensors may be better than larger format older ones.

How should one select the best sensor for any application? It may depend on the available illumination, if fairly constant (CMOS preferred) or widely variable (CCD preferred). Or on the power consumed, where CMOS will be preferred for battery fed cameras. Or on the picture quality, where CCD may be preferred.

The best procedure would be to judge which of the performances given by two cameras having different sensors is more acceptable for a definite situation, while all other elements of the system remain unchanged. Cost also may definitely matter.