[HDRI] CanonHDRcap exposure determination

[Mark Banas (lists)]

Here is one for Greg (of course):

How does CanonHDRcap determine the "minimum" exposure that is  
relevant for an HDR capture dataset?
 From my observations it seems to "search" for the darkest exposure  
where a min. % of pixels are "blown out" and then start marching up  
the exposure scale from there based on your spacing and # of shots.  
I'm sure this is an over-simplification of things, but I tried (in my  
"tethered-to-a-G5-tower-in-a-windowless-office" tests) to find that  
threshold of minimal % where the limits of my camera's shutter speed  
would be hit.

Since I'm stuck inside with my workstation, the "best and brightest"  
to focus on is a 22w halogen bulb on the ceiling track lights. It  
seemed that under certain "ideal" camera conditions (f/8, ISO 100)  
the "searching" would stop at 1/500 sec., regardless of the step  
amount for searching (and 1 stop search takes a while). If I shot  
additional images I could march down to 1/2500 sec. and still have  
nearly the same # of blown out pixels in the image (after that I  
started to resolve the bulb and reflector).

I then checked to see if the captured image resolution has anything  
to do with it (a strict # instead of %) and found no difference. When  
I tested it under tungsten bulbs, it started the series at the point  
where *no* pixels were blown out, but perhaps this is due to my  
camera settings and the dimmer bulb. Again, this is without a laptop  
to go out and sample some serious range, but I'm working on that...

BTW, I shot 13 HDRs in 2 hours, including a disappointing panorama of  
the dusty floor of my office (without being able to "lock" in the  
settings after a "search," multi-shot panos are impossible - the  
range keeps adjusting).

-Mark