Film versus DSLR dynamic range

Started Jul 24, 2007 | Discussions thread
Pierre Sottas Contributing Member • Posts: 787
Re: Bit depth and dynamic range...

Jay Turberville wrote:

Sure. It is possible. But show me one manufacturer who is doing
that when they record their raw data.

all CMOS sensors are able to do that during pre-amplification before AD conversion at the price of loosing some resolution (-> an intelligent form of "binning"). I know that recent Canon CMOS sensors have this property, and Kodak has recently filled a patent with a similar idea:
http://www.wipo.int/pctdb/en/wo.jsp?IA=WO2006130518&wo=2006130518&DISPLAY=DESC

There is some slight non-linearity in real life in the darkest
shadows which is probably due to lens flare. That probably explains
why we can actually reach and even exceed a tiny bit the theoretical
DR limits. You can see that slight non-linearity in this Imatest
graph. It is interesting on its own merits, but I don't think it has
much relevance to practical photography with most cameras. Note the
otherwise linear response.

You suggest that one cannot exceed 12 stops because of the linear response. This is false. Mario is right on this point. You can have an output very close to linear but some non-linearities applied before AD conversion. Read the graph of the 1DMkII: the maximum value is not achieved at the lowest (basal) ISO value but one-two stops higher. This is because of the 2-steps amplification (one before AD conversion at the pixel level and the second (linear) after AD conversion). As a result, I would not be surprised to see that the 1DMkII has slightly less resolution at its basal ISO settings.

Pierre

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