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RTI results blurry because of windy weather???


Sigmund

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Hi!

 

Until now I worked with carved stones in a museum. Today I made RTIs of an erected carved stone outside for the first time. The results are OK but when I zoom in I realize that it is slightly blurry. I use a good tripod for the camera and two cheap microphone stands for the spheres. The stone was erected in a kind of garden so the stands and the tripod were standing on grassland - I tried to fix them as firmly as possible. Today it was quite windy. Not really stormy but it was blowing quite strong from time to time.

 

Now I wonder if the wind could be the reason for the slightly blurry results? Does anybody have similar experience? In addition, I turned the image stabilization (steady shot) out. This can't be the reason, can it...?

 

Thanks for all replies!

 

Sigmund

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Hi Sigmund,

 

It sounds likely that the wind and less than firm ground caused some movement of the camera--it doesn't take much.  You don't want to use image stabilization, regardless of the conditions, so it's good that you turned it off.  This is mentioned in the Highlight RTI Capture Guide.  Using image stabilization actually causes problems with image alignment, counter-intuitively.  One of the reasons for using two spheres instead of just one is that it provides redundancy in the event that one of the spheres moves during the capture sequence.  They will also be useful with the CARE tools, when they become available (parallax causes the light positions to be recorded slightly differently on the two spheres).

 

Try using sandbags or other improvised weights to help stabilize the tripod and stands.  Also, using spikes on the bottoms of the tripod can help provide more stability on slightly soft surfaces (but you want to really push them into the surface).  If the tripod is on a really loose surface, you'll need to take extra care.

 

As long as no individual elements in the scene moved independently (for example, the spheres), there are techniques for aligning the images.  I put a guide for doing this with PTGui into my Dropbox folder here:  http://tinyurl.com/rti-align

I haven't tried this yet, myself.  I understand there are also ways to do this in Adobe Photoshop and that CHI is working on an Imalign tool.

 

Best of luck!

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  • 3 weeks later...

Dear Taylor,

 

thank you for your advice! I tried it today - it was windy - with weights and the results are perfect.

 

Techniques for aligning the images would be a very helpful thing. I will try PTGui - thank you.

 

CHI is working on a  tool? This is interesting. Can anyone tell more about it?

 

Best regards from the Baltic

 

Sigmund

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Our collaborators at Princeton University for the CARE tool project are developing an image alignment tool called Imalign that is specific to RTI (and AR) data sets. We have been testing a beta version. We need to do some work to get the process history tracking right, and to get a user guide created, and similar tasks. Getting out updates to some of the other software has been a higher priority lately (stay tuned for new RTViewer and RTIBuilder updates, and a new capture Guide) We are hoping to get some more work done on the Imalign tool this summer so that it can be released. There are other ways to align images, but none of them is really doing what is needed for RTI, and so you are working around tools that were built for other purposes. We have used PTGui (I'm attaching here a guide for working with that created by another CHI collaborator, Greg Downing) It's a bit painstaking - but it works. Photoshop has alignment tools, but they aren't really set up to align 40-50 hi-res images and the whole thing is brought to it's knees, so it is very cumbersome. The Imalign tool has very useful features for correcting a variety of issues. We'll tell you more when we get closer to a release date. Carla

Stabilizing minor camera shifts for PTM using Image Stitching.pdf

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