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

[Ferrell McCollough]

I would also think that continued overexposure of the scene would cause the 
dreaded color shift (aka hockey stick effect) at the high end of the tonal 
region to "spread" across the scene. Is the HDR merging designed to ignore 
the highest tonal region where color shifts are found?

Ferrell



----- Original Message ----- 
From: "Geraldine Joffre" <hdr-photo at hdrsoft.com>
To: "High Dynamic Range Photography" <hdr-photo at hdr-photography.com>
Sent: Saturday, February 17, 2007 8:38 AM
Subject: [HDR-photo] Number of exposures - Was: Re: Following on 
questions...


> 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
>
> _______________________________________________
> HDR-photo mailing list
> HDR-photo at hdr-photography.com
> http://www.hdr-photography.com/mailman/listinfo/hdr-photo