When you are shooting indoors, the image quality is often very poor. The reason for this loss of detail has a name: digital noise.
Most cameras perform well in daylight, so it’s often difficult to tell the difference between a shot with a compact and an SLR. But indoors or when the light is scarce, the rules of the game are changing: the most entry-level devices are much more sensitive to a phenomenon: digital noise.
Grain and Digital Noise
As you can see above, digital noise is the gradual degradation of image quality as the ISO sensitivity of the sensor is increased. In the days of silver, this noise was called “grain” because it referred to the silver grains of the black & white film where the size of these salts was the amount of light to which they were sensitive. The larger the crystals, the more sensitive the film was but the less detailed it was. Conversely, the very detailed films consisted of small crystals and therefore, not very sensitive.
In the digital age, all pixels of the same sensor is the same size (with a few exceptions), so it is not their size that causes this loss of detail in the image. The main fault is, in fact, the energy circulating in electronic circuits. At the lowest value of the ISO scale, which is also called the sensor’s nominal sensitivity, the electric current is low and does not interfere with image capture. But the light is scarce, the lower the intensity of the signal received by the sensor: it is, therefore, difficult for the latter to perceive the image.
The Intensity of the Current in the Sensor
Photosites, improperly called pixels, capture the luminous information and translate it into an electrical signal. However, to properly distinguish the low-light image, the camera must amplify the signal received by the sensor by increasing the ISO sensitivity, which is reflected by that of the electrical intensity sent to the sensor. It is this intensity that causes interference with the electrical information sent to the sensor. These interferences take the form of the famous “digital noise”.
To combat this noise, manufacturers are constantly improving the components, it is the microlenses on the surface of the sensor to capture more light, the quality of the electrical circuits near the sensor or the image processing algorithms.