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#1 Benjamin Knight

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Posted 02 January 2007 - 12:53 PM

Full disclosure: I?m not really a cinematographer yet; I just edit.

In the Miami Vice DVD commentary Michael Mann talks about the fundamental difference between photochemical cinematography, which he characterises as ?protecting the blacks?, and digital cinematography, ?protecting the whites?; this time from ?clipping?.

Could you point me in the direction of a beginner?s resource that covers this difference? It can get technical quickly, if that helps.

Thanks in advance.
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#2 David Mullen ASC

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Posted 02 January 2007 - 01:05 PM

He's vaguely referring to the old rule about shooting negative film (which doesn't work for video): "expose for the shadows, print for the highlights." Film negative has much more tolerance for overexposure than underexposure that's better to err on the side of more exposure (density on the negative) than the opposite. Digital has to opposite problem: it is more tolerant of underexposure than overexposure so it's better to err towards underexposure.

The problem with both digital cameras and digital sound is that they just unnaturally cut-off ("clip") a signal when it gets overloaded / overexposed.

Film negative responds to light in a non-linear way -- instead of a straight diagonal line (linear) on a graph charting an equal increase in density for every increase in exposure, it's an s-shape that is called a "characteristic curve" (logarithmic).

http://en.wikipedia....Driffield_curve

The middle is straight-lined, but the ends flatten out, meaning that density builds up more slowly in extreme under and overexposure. This has the effect of causing overexposure detail to more gradually burn-out to white. Video cameras can simulate this by applying "knee compression" to the top of the linear response, artificially lowering the amount of signal generated by the exposure, but it doesn't provide the same overexposure range that negative film provides. If enough exposure information is provided by the digital camera, the signal can be shaped into film-like Log shape similar to a scan of a film frame.
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