The luminance range, recorded may be reduced from the luminance range, scene intentionally and/or by the limitations of the recording system. Most systems have a maximum effective signal level limiting the high end, and noise limiting the low end. All of the scene that is of interest must be placed within these two limits by the choice of an appropriate transfer function. Some analogue functions permit gradual transitions to overload and/or noise. Digital functions have inflexible limits imposed by the number of levels permitted by the bit assignments.