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Thread: Preventing Subtle Nadir Seams

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Panotracks

Posts: 32
Location: Florida, United States
Registered: 19 Oct 2012
Preventing Subtle Nadir Seams
Posted: 7 Nov 2012 at 17:47 GMT
updated: 7 Nov 2012 at 17:47 GMT
Shooting Nikon D800 with 16 mm fisheye (6x+Z+N), I'm getting great results in general in PTGui-control point distances around 0.5 to 1.5, including the zenith and nadir shots. However, I noticed on some images such as those that contain gravel, asphalt, sand, etc., that we get a subtle seam at the bottom of the pano. You can see it just to the right of the arrows in this image:

bit.ly/WB1tOc

The seams are extremely difficult to notice in the final pano, but I don't seem to find them on other type of images, such as tiled floors, etc. I doubt the casual viewer would ever notice them. But, other than retouching them in Photoshop, it'd be good to know if anyone has suggestions on how to prevent them from appearing. (I try to get things to work straight out of camera and PTGui rather than bring things into Photoshop if possible.) I'm using a Nodal Ninja R1 + R4, and the nadir shots are offset in viewpoint from other shots, so this is probably related.

Any ideas are appreciated!
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Panotracks

Posts: 32
Location: Florida, United States
Registered: 19 Oct 2012
Re: Preventing Subtle Nadir Seams
Posted: 7 Nov 2012 at 18:12 GMT
It might also have to do with focus on the nadir shot vs. the other images, so I'll look into that and report results here later.
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DennisS

Posts: 1787
Location: Los Anglels, United States
Registered: 1 Sep 2007
Re: Preventing Subtle Nadir Seams
Posted: 7 Nov 2012 at 18:20 GMT
Panotracks,

PTGui's blender has difficulty with situations as you described.

The only way I have found around this is to do two stitches. One with PTGui (name the file TOP) and Smartblend (name the file BOTTOM).

Bring the two images into Photoshop and copy the top portion of TOP over the BOTTOM image. Use layers to blend the seam.

Smartblend does a much better job of blending dirt and gravel and such BUT cannot blend across the Zenith.

PTGui does a great job of blending from the center of the image and up across the Zenith.

By manually blending two stitched images you get the best of both worlds.

For a different issue, if you can see that the Nadir shot is sharper than the bottom of each of the side images, you may have to blur the Nadir shot a bit prior to stitching. Otherwise you might see a seam along the edge of the Nadir shot and the side images. This is not always required, but I run into it a lot.

Dennis
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Sam Rohn

Posts: 321
Location: Brooklyn, New York, United States
Registered: 5 Mar 2008
Re: Preventing Subtle Nadir Seams
Posted: 8 Nov 2012 at 0:19 GMT
i've seen this too, easy enough to fix w a bit of quick cloning on bottom cube face

adjusting seam positions via masking tools may help as well

sam

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Bob Stone

Posts: 387
Location: Rochester, NY, United States
Registered: 20 Oct 2007
Re: Preventing Subtle Nadir Seams
Posted: 8 Nov 2012 at 2:39 GMT
updated: 8 Nov 2012 at 2:43 GMT
Also have seen this but it seems a recent thing. I don't remember anyone having this issue a year ago (or earlier). At one point I was wondering if PTGui made a change to their blender recently. I don't think it's focus related as all areas on both sides of the seam look to be equally sharp.
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John Houghton

Posts: 3934
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
Re: Preventing Subtle Nadir Seams
Posted: 8 Nov 2012 at 7:17 GMT

Panotracks said:

Shooting Nikon D800 with 16 mm fisheye (6x+Z+N), I'm getting great results in general in PTGui-control point distances around 0.5 to 1.5, including the zenith and nadir shots. However, I noticed on some images such as those that contain gravel, asphalt, sand, etc., that we get a subtle seam at the bottom of the pano.

The blurry seams are the result of misalignment of the images in those areas. You should put control points in those areas (using the "Generate control points here" option) to help the optimizer improve the alignment. Given that the R1 setup cannot correct parallax perfectly both at the nadir and the horizontal level at the same time, you may want to move the camera backwards a little to favour the nadir. Possibly you don't have anything close to the camera at the horizontal level, so parallax there should be much less of a problem. As has already been suggested, Smartblend provides an effective solution to the blurring, but can replace that with noticeable double imaging if the parallax is really bad. A good nadir shot can also help by simply covering up the bad seams. However, you can get blurry seams at the edge of the nadir shot too! Recourse to manual blending in Photoshop may be necessary by using the warp tool to fine tune PTGui's alignment of the nadir, working with rectlinear views extracted from the panorama and aligned nadir.

John
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DemonDuck

Posts: 418
Location:
Registered: 10 Mar 2011
Re: Preventing Subtle Nadir Seams
Posted: 8 Nov 2012 at 19:55 GMT
Blurry seams in the nadir are really hard to totally eliminate. If you look close (pixel peep) at even the best panos, you can usually find some blurryness in a seam somewhere. Masking carefully and lots and lots of control points can do a lot to minimize.

Also, the Sharp/Soft feather slider can help. Sometimes setting the slider to sharp can minimize the blur on some textures. Joost recommends two panos. One with Sharp feather for nadir and one with Soft feather for clouds/sky in zenith. Then blend the best from both together.
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Juergen Schrader

Posts: 229
Location: Germany
Registered: 14 Jul 2006
Re: Preventing Subtle Nadir Seams
Posted: 18 Nov 2012 at 23:05 GMT
I second John, and from my experience I can tell that it's not an issue of the blender. With a full frame fisheye or rectilinear lens, a proper setup and of course a stable shoot and correct controlpoints these seams won't appear.

But due to the nature of things there are several sources that may influence the outcome, and sometimes there is no other way then to fix it manually.
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DennisS

Posts: 1787
Location: Los Anglels, United States
Registered: 1 Sep 2007
Re: Preventing Subtle Nadir Seams
Posted: 19 Nov 2012 at 1:20 GMT
John and Jeurgen are spot on. Since 99% of my panoramas are done on a monopod I never maintain perfect alignment. I am so used to fixing the seams. I forgot that with proper pano head/tripod calibration and a good workflow the seams should not appear in the first place.
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Panotracks

Posts: 32
Location: Florida, United States
Registered: 19 Oct 2012
Re: Preventing Subtle Nadir Seams
Posted: 20 Nov 2012 at 16:48 GMT
Thanks, folks-I believe I have solved the problem doing just what you suggested.
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