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Author Topic: Perplexing Panorama Photograph Problem  (Read 6771 times)
sharperstill
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« on: July 19, 2013, 01:08:00 AM »
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Hi,
I've not done a huge amount of stitched panoramas in my life, but have found them to be not too problematic until now.
I was road testing my new Canon TS 17mm and thought I'd womp together a stitched pano at a nearby swamp to see how it'd look.
See attached, and notice the two distinctive bumps on the horizon line. The power lines to the right of the nearest tower are also very mis-aligned.
I was reasonably careful when levelling the tripod head.
Any clues where I let this one get away?
The two version are two different panorama modes in Photoshop, but virtually identical.

Jon
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BartvanderWolf
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« Reply #1 on: July 19, 2013, 02:09:23 AM »
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Hi,
I've not done a huge amount of stitched panoramas in my life, but have found them to be not too problematic until now.
I was road testing my new Canon TS 17mm and thought I'd womp together a stitched pano at a nearby swamp to see how it'd look.
See attached, and notice the two distinctive bumps on the horizon line. The power lines to the right of the nearest tower are also very mis-aligned.
I was reasonably careful when levelling the tripod head.
Any clues where I let this one get away?

Hi Jon,

Hard to say, because of the black-box approach of Photoshop. In my experience, which is extensive when it comes to Pano-stitching, Photoshop can do an okay kind of job, as long as the input is not too problematic/challenging.

Input can be problematic if there is no EXIF data, or the images have been cropped or distorted before stitching. Photoshop can also have a problem with Tilt and Shift lenses, especially with when shift was applied. Also when there is very little overlap between the images and they were not rotated through the axes at the location of the entrance pupil of the lens, it may be impossible to align both foreground and background detail.

A dedicated stitching program should not have too much problem with most of that, and even leveling should not be absolutely necessary, also because the program would allow to manually tweak the parameters that need to be used to get a better result. Photoshop doesn't allow adjustment of parameters, so if it works it works, but if it doesn't, you're usually stuck. All that then remains is editing with e.g. the Warp tools.

If the problem you experience is caused by missing EXIF data, you could try and paste a copy of the image in an image that has the same camera settings, especially knowing the correct focal length is important for stitching. If the problem is caused by (some of) the images having shift applied, you can pre-process the image tiles by adding some transparent Canvas space to each one of them, enough to vertically center the real horizon in each image.

For problem images, you could also try a free very capable dedicated stitching program such as Hugin, which does allow lots of manual intervention. It can also use better resampling algorithms than Photoshop, and that will produce sharper output.

Cheers,
Bart
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keithrsmith
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« Reply #2 on: July 19, 2013, 02:09:56 AM »
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could be distortion from the lens - see if the lens distortion correction makes a difference.

could be mismatched stitching - maybe ptgui would do better as you can define the stitching points.

keith
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Tony Jay
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« Reply #3 on: July 19, 2013, 02:28:10 AM »
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Perhaps a silly question but are the 'bumps' actually represented in the geography?

Another question: Are the seams of the stitches overlapping the 'bumps'?
You did not mention in the original post how many images were used to stitch the panorama.
If there were only two then those bumps are not due to the stitching.
Three images stitched may be responsible.

From a technical perspective you also did not mention whether you rotated the lens or used the shift ability of this lens.
Also, you may have leveled the lens and camera appropriately but that in itself does not guarantee a good result.

I think that if you explain your technique in enough detail we could probably work it out but currently there are so many variables involving both shooting and post-production as to make it impossible to guess.

Tony Jay
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BernardLanguillier
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« Reply #4 on: July 19, 2013, 02:36:35 AM »
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You should try autopano pro of PT gui.

Cheers,
Bernard
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NikoJorj
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« Reply #5 on: July 19, 2013, 06:12:58 AM »
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A typical and quite annoying quirk of PS' Photomerge, as far as I can see.

Go to a better panorama stitcher - one could add Hugin to Bernard's answer.
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Nicolas from Grenoble
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jrsforums
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« Reply #6 on: July 19, 2013, 07:04:06 AM »
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You might want to try 'Puppet Warp' to the stitched image to correct the humps.
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John
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« Reply #7 on: July 19, 2013, 07:32:19 AM »
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In french, we'd call that a plaster on a pegleg. Wink

But yes, I'm afraid it could be the only hope within PS.
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Nicolas from Grenoble
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wolfnowl
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« Reply #8 on: July 19, 2013, 02:54:26 PM »
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Sometimes you can get 'interesting' results!

http://www.wolfnowl.com/2010/05/panoramic-photography-and-stitching-errors/

Mike.
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Eric Myrvaagnes
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« Reply #9 on: July 19, 2013, 04:28:19 PM »
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Gosh, Mike! You've got a great new creative tool there! The "fix" on the second shot is my favorite.

Eric M.
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LesPalenik
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« Reply #10 on: July 20, 2013, 12:01:43 AM »
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It would be useful to know how many frames you used, and what was the overlap.
As mentioned by another poster, it could be caused by the lens distortion. If you can repeat the stitching experiment, you might find your answer by looking at the individual layers and then correlate the stitching lines with the problem areas in the final image.

Most stitching programs put priority on the alignment of individual segments, not taking into consideration the lens distortion or blurry edges.
For example, they may use the leftmost and rightmost images almost in their entire lengths, while discarding a lot of information from the neighbouring frames with much sharper and less distorted data.
   
To counteract it, sometimes I crop the individual images on both sides, thus eliminating the greatest distortions, and forcing the stitching program to use only the best portion of each frame.
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sharperstill
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« Reply #11 on: July 20, 2013, 06:23:38 AM »
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Thanks for the replies everyone and sorry for the delay in responding - blame the time zone and a busier than expected day yesterday.
Some points raised by respondents.
It was 4 images used to generate the panorama and overlapped a third of the frame
The lens was shifted upward slightly. I can't remember the exact amount but at a guess probably shifted half-way. There was no tilt applied.
The camera was positioned on a 'nodal slide' in a position I had worked out earlier from the two-candles-on-my-dining-table method.

"Input can be problematic if there is no EXIF data" - The file is on my other computer, but I imagine the EXIF data was intact. The RAW files were imported into Lightroom then all four selected and sent to Photoshop to Merge to Panorama.

"could be distortion from the lens - see if the lens distortion correction makes a difference." - I didn't think lens corrections could be applied to images from TS lenses?

"Perhaps a silly question but are the 'bumps' actually represented in the geography?" - No, it's pretty flat, it's a wetland...

I ditched the panoramas after  outputting the lo-res composite but had a look at the masks that Photoshop had made before doing so. They were weird. Previous panoramas (3 frames) that I've done with the 24TS PS used each image in one 'slice' but in this one there was one frame used where PS had selected several separate 'islands' of data from that frame only, including two that were really quite small and of insignificant areas.

I've downloaded Hugin, and will process the files in that and report back.

Cheers,

Jon
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BartvanderWolf
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« Reply #12 on: July 20, 2013, 07:00:44 AM »
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The lens was shifted upward slightly.

Hi Jon,

Well, as expected there's your problem, it confuses Photoshop.

Quote
I've downloaded Hugin, and will process the files in that and report back.

Once you've gotten a bit acquainted with the application, the solution for your issue is in the 'y shift (e):' parameter of the Optimizer Tab. Typically, you'd do a regular stitching optimization (which may get similarly confused as Photoshop), switch-off the optimization for all other parameters, then only optimize the 'y shift (e)' parameter, switch it off again, and do another regular optimization of only the other parameters again.

Once things improve, you can be so bold as to optimize the lot of parameters, but with so many variables, it can also result in total chaos. So make sure you save the project file between optimizations, before you accidentally lose the Undo capabilities ... It's not a question of if, but when ...

When you make a note of the shift quantity applied to the lens, it's easy to transfer that amount to the optimization parameter. A shift of 1mm on a 36mm sensor in portrait orientation, leads to an image pixels in height x 1/36 offset. You'll have to figure out if it's a + or - offset depending on the shift direction used.

Also note that, for a dedicated stitching application it is not absolutely necessary to shoot level and compensate for key-stoning or such by shifting the lens. It can help to get a better coverage of the sensor real-estate because no cropping is required afterwards, but mathematically it make no difference for the Pano-Stitcher.

Cheers,
Bart
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sharperstill
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« Reply #13 on: July 20, 2013, 07:54:25 AM »
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Thanks Bart,
Definitely sounds less 'black box' than Photoshop. I'll give the same files a go over the next day or two.

Jon
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BartvanderWolf
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« Reply #14 on: July 20, 2013, 08:42:21 AM »
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Thanks Bart,
Definitely sounds less 'black box' than Photoshop. I'll give the same files a go over the next day or two.

Hi Jon,

Absolutely less 'black box'. But the downside to more control is also more opportunities to make an even bigger mess. Hence the practical hints.

Cheers,
Bart
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OldRoy
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« Reply #15 on: July 25, 2013, 04:32:36 AM »
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Quite astonishing how the canard of "tripod levelling" recurs when stitched panos are discussed. As if, within reason, it mattered when you are remapping every pixel in the final image. As far as I'm aware all stitching software (I'm only familiar with PTGui Pro) has the inherent capacity to level the final image.
Roy
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Ellis Vener
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« Reply #16 on: July 25, 2013, 01:34:43 PM »
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Photomerge has gotten better with each iteration of Photoshop and it is to the point now where I try Photomerge in Photoshop CC before turning to PTGui Pro. Photomerge is still mostly a simpler "blackbox" as far as fine tuning the controls while PTGui Pro approaches infinity in terms of ability to tweak the workings.

If you have PsCS6 or Ps CC check out this video by Russell Brown on the Adaptive Wide Angle filter: http://www.youtube.com/watch?v=0LUlpj4DqIo  at 7;12 he directly discusses using it with panoramas and why he uses it now instead of Puppet Warp
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Ajoy Roy
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« Reply #17 on: August 08, 2013, 09:25:56 AM »
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I have done extensive stitching using my cell phone camera for various site related jobs. I have used both Hugin and Microsoft ICE. The problem with bumps always occurs on both when
. Taking a pano of a long beam head on - distance is quite short
. Taking a pano of a long wall head on

I have tried 20% to 80% overlap, but nothing helps in either of these software. The only remedy is to tape panorama shots at an angle, or use a software where you can specify a horizontal/vertical alignment line

You can see that there is a disjoint in the centre
« Last Edit: August 08, 2013, 09:28:19 AM by Ajoy Roy » Logged

Ajoy Roy, image processing
BartvanderWolf
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« Reply #18 on: August 08, 2013, 04:39:25 PM »
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I have tried 20% to 80% overlap, but nothing helps in either of these software. The only remedy is to tape panorama shots at an angle, or use a software where you can specify a horizontal/vertical alignment line

Hi,

Hugin allows to specify horizontal/vertical lines. When the images were taken with some care, even handheld images can often be stitched by using the offset parameters (Image center shift: d and e), and for flat surfaces the X, Y, Z parameters.

Cheers,
Bart
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AreBee
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« Reply #19 on: August 09, 2013, 02:51:50 PM »
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Ajoy Roy,

Quote from: Ajoy Roy
I have tried...but nothing helps...

Did you place control points manually?
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