Got it. Thanks. Tom C.
>From: Godfrey DiGiorgi <[EMAIL PROTECTED]> >Reply-To: Pentax-Discuss Mail List <[email protected]> >To: Pentax-Discuss Mail List <[email protected]> >Subject: Re: Silly HDR Question >Date: Sat, 4 Nov 2006 14:38:53 -0800 > >No, that's not the right way to think about it. Read what I wrote >below carefully. > >The sensor has an absolute dynamic range. Exposure settings establish >the environment in which that dynamic range operates electically, >essentially setting the gain "window" over which the sensor can >capture intensity values. You can adjust what HAS been captured >within certain boundaries mathematically after the fact, which is >what you're doing when you modify the gamma correction curve in a RAW >converter, but you cannot change what has been captured. That can >only be adjusted by exposure at the time of capture. > >An HDR technique of taking multiple exposures at different settings >than merging them together allows the sensor's absolute dynamic range >to be extended, synthesizing a larger dynamic range through repeated >and different 'windows' on the subject intensities. > >Godfrey > >On Nov 4, 2006, at 1:56 PM, Tom C wrote: > > > What you say makes sense excpet when I think of it like this: > > > > I was thinking of the data captured by the sensor as basically a > > bitmap. If > > all adjusting gain (up/down) on the sensor effectively does, is to > > make an > > individual pixel, lighter or darker than it would have been > > otherwise, then > > it *seems* that the same thing could be done post-capture, sans- > > sensor. > > > > So is my thinking basically correct in principle, but not > > necessarially so > > in practice? > > > >> In simple terms: > >> > >> - Making one exposure and than adjusting it once out of the camera > >> always locks you into whatever happens to be the maximum analog > >> dynamic range of the sensor. If elements of a scene fall outside that > >> dynamic range, you get black/noise or total saturation, no matter how > >> much adjustability a RAW converter might have or how much data > >> recovery it can do. > >> > >> - Making a set of exposures at different exposure settings and then > >> integrating them together allows you to window the scene with a > >> dynamic range wider than what the sensor can acquire in one exposure. > > >-- >PDML Pentax-Discuss Mail List >[email protected] >http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
