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"Sensitometric behaviour" of image sensors.

johngie

Mold, UK
300 posts

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johngie Registered since 07th Jul 2007
Mon 31-Aug-09 04:00 PM

Hi folks,

This is a fairly technical question but I hope someone will be able to throw some light <G> on it!

Film has a sensitometric curve (the D logE curve) that is non-linear: it has a gentle toe, with the slope of the curve (i.e. the contrast) increasing at the mid-point of the exposure range and then decreasing again at high exposures (the "shoulder"). This is what made film fairly "forgiving" and these curves were exploited superbly by Ansel Adams in his Zone System. Indeed he developed his films individually to make the film curve fit his subject brightness range!

I'm making the assumption that a digital image sensor characteristic is basically a straight line between full black and a highlight at which it starts to clip. (Is that correct?). No gentle toe or shoulder, just "hard clipping" at the extremities.

I also presume that HDR techniques aim to emulate the gentle toe and shoulder.

My last question (as it applies specifically to the Nikon) is:
If I choose the lowest contrast possible in my Picture Control, does that enable the sensor to cover a greater dynamic range? Or does it keep that fixed but just reduces the contrast?

Regards

John Gruffydd
Mold, Wales, UK
D300, D200, OM1, OM2n, Bronica ETRSi, Lumix LX5

G