[HDR-photo] Number of exposures - Was: Re: Following on questions...

[Geraldine Joffre]

On Thu, 15 Feb 2007 19:24:05 +0100, John Callan wrote
> In your response to Royce Howland you said...
> 
> >More samples will still help improve the quality of the HDR image, thanks to a
> >more accurate calculation of the HDR values and to the noise reduction
> >benefits produced by averaging.
> 
> If that is the case, are you suggesting that one should always shoot 
> high
> (minimum of 12 - 15) exposures of a subject to allow software to 
> produce a high content image ?
It depends on the dynamic range of the scene and it also depends on how you
define the term "high content image". If the dynamic range spans a four EV
range or less, 12 exposures separated by one-EV or more will be overkill, as
it would add shots that are either too overexposed or too underexposed to be
useful, and may even confuse the HDR merging algorithm.  And then there are
the issues of misalignment and ghosting that become more exacerbated with more
shots, especially if you have to change the shutter speed manually to achieve
the number of exposures.

If your purpose is to produce an image that has the least level of noise
possible, then stacking a lot of shots of the same scene makes sense. But you
will have to make sure to adjust the EV-spacing to the dynamic range of the
scene, or even take some of the shots at the same exposures if the dynamic
range does not justify more.

Geraldine Joffre