Using the following formula (see also Dynamic range), it can be calculated that a linear 8-bit image with 256 brightness levels can no longer be imaged with a roughly 48 dB dynamic range:

To be able to display a dynamic range of 120 dB in an image with a linear characteristic, for example, a bit depth of 20 bits (1 million brightness levels) would be required accordingly. For this reason, the image data must already be available before digitization with a logarithmic characteristic that carries out dynamic compression in pixels. This is why a logarithmic characteristic is aimed for with HDR sensors.

Fig. 47: Image capture with a logarithmic sensor