For a scanner to accurately reproduce an original, it must be able to register the complete density range present. Getting tricky Exposing a film to increasing light levels raises the opacity or blackness of its emulsion after development. The opacity of a film is defined by the total amount of light falling on it, divided by the amount transmitted through it. You can use the same calculations for reflective materials. If a printed area on paper gives 50-percent light reflectance, its opacity is 2.
Opacity is the inverse of transmission or reflectance.
An opacity of 2 results in a transmission or reflectance of half of the incident light. For this reason, the term density was introduced, which directly corresponds with the thickness of a filtering layer. Transparencies generally have a Dmax of about 3.3 and a Dmin of 0.3, giving a density range of 3.0 D. Reflective materials may have a density of 2.0 D, but in most cases the range is nearer to 1.7 D. Because transparencies contain a tonal range 10 times wider than reflective materials, they require scanners that are far more sensitive. Becoming fluent Before scanning any original, you should check whether it contains a restricted tonal range or unusual color balance. More likely it was overexposed or poorly processed.