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Author Topic: Stitching question  (Read 5565 times)

tsjanik

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Stitching question
« on: March 28, 2011, 06:29:44 pm »

I have little experience with stitching and so far photo merge in PS has been fine.  I recently stitched 5 exposures taken with a Pentax 645 35mm lens.  The lens has some barrel distortion, which apparently manifests itself as a wavy horizon in a stitch.  Any cures for this?
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Kirk Gittings

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Re: Stitching question
« Reply #1 on: March 28, 2011, 10:51:04 pm »

You can correct the barrel distortion before the stitch and eliminate some of this. I do this in LR3 first and then open the corrected files in PS5 for stitching. I think you could also do this with ACR.
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Thanks,
Kirk Gittings

BernardLanguillier

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Re: Stitching question
« Reply #2 on: March 28, 2011, 11:07:08 pm »

Wasn't there an option in CS5 to correct for distortion?

Or you can try the try out version of Autopano Pro, my guess is that you will have no issues.

Regards,
Bernard

Bart_van_der_Wolf

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Re: Stitching question
« Reply #3 on: March 29, 2011, 03:43:59 am »

I have little experience with stitching and so far photo merge in PS has been fine.  I recently stitched 5 exposures taken with a Pentax 645 35mm lens.  The lens has some barrel distortion, which apparently manifests itself as a wavy horizon in a stitch.  Any cures for this?

Hi,

A wavy horizon is usually caused by a (slightly) non-plumb orientation of the vertical axis of horizontal rotation. IOW, the tripod was probably not level (although is can also be introduced by the software). Fortunately this is less of an issue if you use a dedicated panostitcher software which allows to adjust the vertical position of the virtual horizon in the stitch.

Most panostitchers automatically correct for barrel/cushion/combined lens distortion, but as suggested you can also make sure your image tiles are properly corrected, which allows to also reduce vignetting for each tile. It will only make the automatic stitching easier and reduce the need for further manual touchups.

Cheers,
Bart 
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tsjanik

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Re: Stitching question
« Reply #4 on: March 29, 2011, 10:21:05 am »

Thanks for pointing me in the right direction fellows.  I don't use LR, since I was primarily using film and I'm somewhat embarrassed to admit I was unaware of the lens distortion feature in later versions of PS; having learned to use transform the few times when I wanted to correct distortion. 
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fike

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Re: Stitching question
« Reply #5 on: March 29, 2011, 12:35:28 pm »

In some panorama software (PTGUI is the one I use) in addition to specifying control points, you can specify lines, horizontal or vertical.  You can specify the line that is made by the horizon across two different images in much the same way that you would manually place a control point.

Water is difficult for panorama software.  The shape of the surface of the water is constantly changing so you don't have the ability to easily create control points where the subject hasn't moved. I often find that I need to manually enter control points in approximately the right position and then manually blend the water to make sure it doesn't show blending lines.

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scrinch

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Re: Stitching question
« Reply #6 on: March 30, 2011, 06:58:19 am »

I do not know where it is located in CS5 but in CS2 the lens distortion correction is under Filters>Distort>Lens Correction.  It is very effective. 
If you end up with wavy lines after stitching this can sometimes be corrected (again in PS2) Edit>Transform>Warp. 

As mentioned previously, dedicated Pano software usually does the trick better.  I have done pano's freehand standing in my 16' boat with a rolling sea and had good results with Panomaker.  For the best results though, a dedicated leveling Pano head on a tripod can't be beat.

tsjanik

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Re: Stitching question
« Reply #7 on: April 18, 2011, 11:06:45 pm »

Thanks all, fixed the problem.  Not a great image, but a proof of principle.  Crop from far left.  7 shots, 645D, 35mm A
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MichaelEzra

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Re: Stitching question
« Reply #8 on: April 19, 2011, 08:07:28 pm »

Try autopano giga (autopano.net).

You can use the ACR distortion model there on input of raw files.

If input is raw or developed TIF/JPG images you can manually override the lens focal distance value to model a different distortion correction.
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Peter McLennan

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Re: Stitching question
« Reply #9 on: April 20, 2011, 11:24:26 am »

On a finished, stitched image, in Photoshop CS4 and later you can do a SELECT ALL | EDIT | TRANSFORM | WARP  to adjust your wavy horizon.
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marcmccalmont

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Re: Stitching question
« Reply #10 on: April 21, 2011, 05:59:05 pm »

I'm not sure what equipment you are using but investing in a good leveling tripod along with a grid focusing screen will minimize the problem up front. i have also found correcting lens distortion during the raw conversion gives better results in difficult situations i.e. sky, water etc.
Marc
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Marc McCalmont

Bart_van_der_Wolf

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Re: Stitching question
« Reply #11 on: April 26, 2011, 05:39:10 am »

I'll try and get the point across one more time. Wavy horizons are caused by wrong leveling in the stitching software. Even when the camera wasn't perfectly level, the wavy stitching can be corrected by choosing an appropriate horizon (mostly pitch parameter, most likely together with some roll due to sloppy technique) when stitching.

Having said that, there is a benefit to do a proper leveling before shooting. It wil allow to crop less of the info from the final stitch, or reduce the need to (content aware) fill in areas that were not covered by our image tiles.

Cheers,
Bart
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