Transmittance or Density – a Question of Bits?

The question of radiometric resolution is an important one in connection with the introduction of digital systems. The number of available bits is generally given with the note that the achieved radiometric resolution is much superior to that of photographic emulsions. In this comparison it is usually overlooked that film records densities, i.e. logarithmic values, while CCDs record transmittance or reflectance, i.e. linear values. To be able to derive from transmittance or reflectance densities reaching from 0 to 3 with an 8 bit resolution ~13 bits of resolution are needed for transmittances or reflectances. The paper presents results for a black-andwhite digital image recorded using 12 bits which was recalculated from the recorded reflectances to densities assuming different exposures and film emulsion properties defined by the Standards characteristic curve for black-and-white negative silver-based film. It is shown that film, when properly exposed and processed, is able to reproduce the information present in a digital image recorded with 12 bit radiometric resolution.