PanoTools:
Re: dynamic range and noise (yet again)
Erik Krause 2005-Oct-27 18:26:27
On Thursday, October 27, 2005 at 16:04, pedro_silva58 wrote:
> imagine we expose for the highlights, ie, measure exposure so as to
> take the highest important highlight as close to clipping as possible
> without actually clipping. we take, say 8 shots with that exposure
> value (with tripod, remote, etc). if the scene dynamic range is high,
> shadows will be severely underexposed, and mids somewhat underexposed,
> too.
>
> now, we open all 8 images, and add (photoshop-screen?) them together
[...]
> so... does any of this make any sense?
Yes. You just re-invented a commonly used technology to reduce noise
by avaraging several shots. Helmut Dersch wrote PTAverage for that
purpose: http://www.path.unimelb.edu.au/~dersch/average/average.html
He reffered to scanned images of course but the problem is all the
same with any kind of digital images.
Hint.: Adding up the images would of course increase the exposure but
since you easily can cross the 8 or 16 bit limit if you don't use a
floating point format it is better to average the values in order to
have them inside the possible range.
However, the technique has it's limits: Camera shake, moving objects
and so on. And of course it's easier to extend dynamic range by
blending multiple exposures: To gain one f-stop dynamic range you
need to double the number of images.
best regards
--
Erik Krause
Resources, not only for panorama creation:
http://www.erik-krause.de/
Read panotools at GMane:
http://news.gmane.org/gmane.comp.graphics.panotools
------------------------ Yahoo! Groups Sponsor --------------------~-->
Get Bzzzy! (real tools to help you find a job). Welcome to the Sweet Life.
http://us.click.yahoo.com/A77XvD/vlQLAA/TtwFAA/.Cr1lB/TM
--------------------------------------------------------------------~->
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/PanoTools/
<*> To unsubscribe from this group, send an email to:
#removed#
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/