[HDRI] Photosphere 1.6 available

[Kirk Thibault]

So if I do a little experimentation ahead of time and establish a  
manual set of exposures, and do that same set across all of the  
images I intend to stitch together, it sounds like Photosphere will  
make the HDRs and combine them in a way that will take care of  
balancing the exposure (tone-mapping exposure) across the panorama.

Also - for anyone trying it out, it took me a few tries to figure out  
that you have to select (click-drag) a small portion of the scene  
when designating matching feature points (versus simply clicking on a  
feature).

Re: barrel distortion - it sounds like if I try to take all of my  
LDRs into Photoshop and use the Lens Correction filter to remove  
barrel distortion, then I will lose important image info that  
Photosphere uses to do its magic.  I'll try a couple of different  
focal lengths with a simple LDR panorama and see what I get wrt  
stitching distorted images.  I'll also try varying the overlap amount.

Pretty cool.

kirk
------------------------------

Kirk L. Thibault, Ph.D.
kthibault at biomechanicsinc.com

p.  215.271.7720
f.   215.271.7740
c.  267.918.6908

skype. kirkthibault




On May 11, 2006, at 2:12 AM, Gregory J. Ward wrote:

> Hi Kirk,
>
> Thanks for the feedback.  I'm happy, and somewhat amazed, that  
> you've figured out how to use it already.  The interface is quite  
> different from other applications, but that's mostly because I'm a  
> really lame GUI programmer....
>
> Lens distortions don't always cause misalignment in panoramas, as  
> long as you overlap where the distortions match.  However, you will  
> get a kind of "waviness" to lines going from one image to the next  
> due to the uncorrected barrel distortion.  You are best off  
> experimenting with a few different lenses to see the results.  I  
> don't really have enough experience at this point to advise you  
> past that.
>
> Regarding image exposure, Photosphere uses the sample-to-nits value  
> (a.k.a. EXPOSURE setting) in an HDR file to rectify the brightness  
> scale between images.  This may not work if your images were  
> assembled by a program other than Photosphere or hdrgen, or if  
> you've manipulated the images with an application that doesn't keep  
> track of this setting.  (Most image editors that work on HDR such  
> as Photoshop CS2 and HDRShop don't.)
>
> For 24-bit RGB (standard LDR) images, you really need to nail the  
> exposure and keep it fixed on manual throughout your sequence.  If  
> if it were possible to correct for different exposures, you would  
> have issues with clamping differently in the highlights in many cases.
>
> The panorama stitcher in Photosphere does a better job than most at  
> hiding gradient differences between images, so things like lens  
> flare are not the usual disaster.  Instead of seeing a seam or  
> strong gradient, you may notice an erratic line where the two  
> images are stitched together.  That's the way this algorithm looks,  
> I'm afraid.  Sometimes it looks better than a smooth blend, and  
> sometimes it's worse.  It really depends on the scene.
>
> -Greg
>
>> From: Kirk Thibault <kthibault at biomechanicsinc.com>
>> Date: May 10, 2006 8:15:24 PM PDT
>>
>> Greg - that is pretty cool.  It is fairly easy to get the idea of  
>> linking one to the next image.  Thanks!  Now I have to go out and  
>> take a bunch of panoramic, multiple-exposure images and see what  
>> happens!  What do you think is the lower threshold from a lens  
>> focal length perspective (haha!) that will still give a relatively  
>> distortion-free stitched image?  i assume we can exposure balance  
>> the HDRs in Photosphere prior to stitching to get even exposure  
>> across the panorama.  Is there a way to get the panoramic exposure  
>> balance automagically?  I guess I'll experiment with it before I  
>> ask any more stupid questions.
>>
>> later,
>>
>> kirk
>
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