| Imabug 2006-02-25, 8:54 pm |
| The answer to your question depends entirely on the manufacturer of the
CR system in question, since they all compute an 'exposure index' using
different methods. Fuji's S values are intended to reflect the
sensitivity used to read a plate and is inversely proportional to plate
exposure. Agfa uses a different logarighmic scale (lgM) with values
that typically range from 0 to 4, with higher values indicating higher
plate exposures. Each change of 0.3 in the lgM value represents a
change in plate exposure by a factor of 2. Kodak uses yet a different
index which has a linear relationship to plate exposure.
Also, CR/DR receptor exposure generally has no bearing on the final
look of the digital image. All manufacturers map the digital image
values so that even an underexposed image will have roughly the same
appearance as a properly exposed image. The only differences between
underexposed, properly exposed and overexposed images are the noise
properties.
|