On 12 Apr., 16:48, Marvin <physc...@[EMAIL PROTECTED]
> wrote:
> Marc Wossner wrote:
> > Dear ng,
>
> > concerning the available luminance range of slide films Hunt writes in
> > 'The Reproduction of color' that
>
> > =A0'...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. =A0In 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.
Well I do have H&D plots of several films/papers in front of me but I
simply do not see how Hunt relates the luminance range of 2,1 log
units of typical slide film (he derives this figure by subtracting
factors like stain, vignetting and so on from the usual max density of
3) to 1,4 log units of scene luminance by introducing the effect of
the dark surround of projection.
Marc Wossner
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