Marc Wossner wrote:
> Dear ng,
>
> concerning the available luminance range of slide films Hunt writes in
> 'The Reproduction of color' that
>
> '...the effect of the dark surrounds in reducing the apparent
> contrast of projected transparencies is such that this range of
> reproduction luminances, 2,1 log units, is equivalent to only about
> 1,4 lof units in scene luminance...'.
>
> Now I understand that slide film must have a high gamma value/steep
> characteristc to compensate for the reduction of apparent contrast
> caused by the dark surround, but can anyone imagine how this affects
> the range of available scene luminances?
>
> Thanks a lot for all your input!
> Marc Wossner
>
>
in film photography, gamma is the slope of a graph with the
x-axis being the exposure and the y-axis a measure of the
response of the film, such as the percentage of light that
is transmitted. In that context, exposure is light intensity
at the surface of the film multiplied by the duration of the
exposure.
The range of the response is a property of the film and the
method of development,so it is fixed. In digital
photography it is a property of the sensor, which is also
fixed. When the gamma is higher, i.e., the line is steeper
(higher slope), the range of exposures that the sensor can
measure is less.
Putting this on graph paper may help you to understand.
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