[HDRI] Re: CanonHDRcap exposure determination

[Greg Ward]

Hi Mark,

> From: "Mark Banas (lists)" <listmail at mab3d.com>
> Date: February 2, 2006 8:30:26 PM PST
>
>> CanonHDRcap works as you surmised, but only looks at the image  
>> thumbnails, not the whole image (which would take too long).  As a  
>> result, it doesn't always pick the right exposure to start with --  
>> if your bright spot takes up less than a pixel in the thumbnail,  
>> it may choose a shutter speed that's slower than it should to start.
>
> Hmmm... so is there any way in the Canon SDK for CanonHDRcap to  
> look at the thumnails *without* transferring the full-res files  
> from the camera over the USB/Firewire cable? For the ones it  
> "keeps" it would simply be writing them to the CF card for later  
> conversion to HDR. This would speed things up for those of us with  
> the low-end cameras, but also for the high-end cameras that can  
> knock out 8+ frames a second!

Indeed, this is what I originally had in mind, but I scaled back my  
ambitions after a little quality time with the Canon SDK  
documentation.  Saving to the card and downloading images later is a  
bit of a hassle, requiring figuring out rather a lot I don't  
currently understand...  If I just left the images on the card, that  
would be one thing, but I need to download them for my application,  
and figuring out which images were saved, where, and how they were  
named, and doing all the associated file management is rather  
painful.  Not having the images written to the card in the first  
place is a whole lot simpler, so that's what I did.  I may get around  
to the more sophisticated method at some point, but don't hold your  
breath.

>> I could be persuaded to add a parameter for the starting shutter  
>> speed.  If set to some positive value, CanonHDRcap would then  
>> start from the specified speed rather than doing its search.
>
> That sounds great for those situations where the range is already  
> "known" and repeatability is required (and I run into that all the  
> time). Actually, what would be great would be for a way in the  
> CanonHDRcap.out screen to have it pause at the end of a cycle and  
> then accept a keystroke to either "repeat" the series of shots it  
> just did with no searching (for multishot panoramas, stitched ultra- 
> res images, or the off-axis shot of a mirrorball), or to "restart"  
> the process (allowing time for on-camera adjustments like aperture,  
> ISO, etc.).

Pausing for input with this stupid interface means using 100% of the  
CPU in a polling loop.  (CodeWarrior and the Carbon library needed by  
the SDK are incorrigible on this point.)  You can always run  
CanonHDRcap in auto mode first, check the exposures, then set the  
camera and put it in manual mode again (by setting the f-stop search  
step to 0).  I just added this feature.

> And then it would also be great to let CanonHDRcap do its magic and  
> find the best starting point and proceed up until it either hits  
> the # of exposures specified, or a shutter speed specified as an  
> "ending limit" (to avoid those 15 sec. exposures).

Hmmm...  I can give you the code, and you can do what you want to  
with it.  I'm not quite so fussy, it seems.

> Of course, the basics are already there (and it works great so far)  
> so really these are situation-specific requests. Thanks a lot for  
> this, Greg. It really will be a time-saver!

The new version with manual control over the starting point is now on  
my website.  I've also made some enhancements to raw2hdr, which works  
for non-Canon cameras as well.

-Greg

P.S.  The URL is still http://www.anyhere.com/gward/pickup/ 
HDRcapOSX.tar.gz