Stitching and exposure bracketing help needed

[michaelbiondo]

Hello, I am shooting arch & landscape, my working method is to shoot  with a dslr mounted onto the rear of a view camera, I  shoot bracketed panoramas, three rows of three frames (landscape orientation) the problem arises when i try to create three, one of each exposure, identical, pixel perfect stitches that I then use to blend together to create one HDR image. I know how to accomplish this using PTGui software but I am finding that the quality of the stitches created with PTgui is not up to par (misaligned elements). I am having much more success using PS3 photomerge BUT, I do not know how to get photoshop to create three identical pixel perfect stitches. Any ideas??

[JeffKohn]

PTGui is assuming that shot the images by rotating the camera, so it's going to do a projection based on that, which doesn't apply in your case. Normally my recommendation is to use Photoshop's Photomerge with the "Reposition Images" option which doesn't do any projection. But as you say there's no way to get PS to stitch a bracketed set using identical stitching.

I believe there's a workaround in PTGui for your situation, though. Disable able the option to read the lens info from EXIF. Then manually set the lens info to something like 1000mm. This has the effect of flattening out the projection to the point where it's almost the same as a flat stitch.

Out of curiosity, which DSLR, VC, and lenses are you using? I've been considering moving to such a setup.

[michaelbiondo]

thanks Jeff, overrode the auto extif lens setting and manually put it at 1000mm but this one particular image is still giving me a bad alignment, lot of repeating clapboard siding on this one particular building I photographed.Attached are jpegs
one thing I have found is that PTgui works better on some images than others
FYI, I am shooting with a cambo ultima 35, canon 1ds mark III, Schneider 28, hassi 50 and hassi 80mm. for the most part I am happy with the rig...

[attachment=20491:AG_2_19_10_shot_7A.jpg]

[attachment=20490:AG_2_19_10_shot_7.jpg]

[JeffKohn]

Yikes, that's pretty bad. I'm surprised PTGui did so poorly, the images should be pretty easy to stitch.

Changing to a different blending algorithm like Smartblend might help, but given the repeating details in your subject getting a clean stitch in the first place is important because the blender can only do so much.

You might try going in and manually adding some control points in the problem areas.

One other option would be to do the blending first, using something like TuFuse, so that you can stitch with Photoshop.

[feppe]

I've done several bracketed nighttime stitches which can be a nightmare to stitch. I've found PTGUI to give the best results - instead of "true" HDR I use exposure blending (I think that's what it's called).

For stitches which cause me heartburn I try Autopano Pro to see if it works better. If all else fails, I go the Tufuse way and blend the images before stitching.

[BernardLanguillier]

thanks Jeff, overrode the auto extif lens setting and manually put it at 1000mm but this one particular image is still giving me a bad alignment, lot of repeating clapboard siding on this one particular building I photographed.Attached are jpegs
one thing I have found is that PTgui works better on some images than others
FYI, I am shooting with a cambo ultima 35, canon 1ds mark III, Schneider 28, hassi 50 and hassi 80mm. for the most part I am happy with the rig...

If I may ask, why do you need HDR for such a shot?

Anyway, I don't do much HDR these days, but always use PTgui's Enfuse implementation when I do (need to correct distorsion after the fact though). A recent sample (no stitch here):



For single bracketed imagesI have never had a single problem stacking up with <0.01 pixel accuracy (PTgui optimizer value) up to 5 images shot taken with my DSLR and a very robust tripod/head. PTgui has by far the best alignement engine on the market for such images.

Now it could be that the combination of HDR and flat stitching was not part of the testing patterns for PTgui and that some problems occur. PTgui was clearly optimized for cylindrical stitching and makes assumptions based on this. It is also not that good at stitching images that have been assembled in DoF stacking software since this modifies the actual focal lenght of the lenses between images. PS works with a more generic pattern recognition engine and sometimes deals better with such non standard cases.

Else, your results might indicate that something is moving quite a bit between your frames:

- the tripod,
- the head,
- your view camera,
- the DSLR relative to the view camera

You would have a lot less problems with cylindrical stitching...

Cheers,
Bernard

[michaelbiondo]

Certainly, for this particular shot there is no need to expand the dynamic range. but when it is needed i mostly use Exposure Fusion, keep the brackets on separate layers and then paint in highlights & shadows as needed.  No doubt about Ptgui being a very serious bit of software, and I do not have this problem with all my images, there must be a workaround for this, I suspect it is a control point issue and will continue researching the topic as it is key to my workflow. I just joined there two user groups, google & yahoo. both are moderated by Carl von Einem (co owner of panotools ng) and  will keep the topic updated.
Thanks,

[EduPerez]

Have you tried using Hugin? There are a couple of tutorials about something quite similar to what you are trying to do, at Stitching flat scanned images and Creating linear panoramas with Hugin.