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Author Topic: Problem with Photomerge  (Read 6387 times)

ternst

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Problem with Photomerge
« on: July 04, 2008, 07:15:17 pm »

Anyone have an idea what I am doing wrong to get the following results - sometimes the image on the right will be distorted, sometimes the image on the left will be distorted. This happens if I overlap a lot (50%), or a little (20%), and if I use two images or three or four. These are 39mp files from a P-45+, running on a Mac, CS3. I have found that if I run photomerge from within Bridge the left photo is distorted; but if I run it from within photoshop right photo is distorted. The images are shot with a variety of lenses, bot norma, tele, and wide, and I have been getting the same results (camera level, etc.). Any ideas what I'm doing wrong? Thanks.

Tim Ernst in Arkansas

Each of these is a merge of the same two files - one done from within bridge and one done from within photoshop. It does the same thing with a four-shot series of this same view.
« Last Edit: July 04, 2008, 07:22:07 pm by ternst »
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Panopeeper

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Problem with Photomerge
« Reply #1 on: July 04, 2008, 09:11:29 pm »

1. There is no distortion here. When stitching images, they have to be warped. The effect depends on the angle of view, horizon, and most prominently on the projection method. What you did is the rectilinear projection, in Photoshop named "perspective".

In this particular case the cylindrical projection might be better, but one needs to understand the implications: vertical straight lines remain straight, horizontal straight lines get warped, except the "horizon".

2. I don't know how you can adjust the arrangement, I am not using Photoshop for stitching (it is for occasional pano makers), but I guess there is some command to set the "center" of the pano.
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Gabor

ternst

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Problem with Photomerge
« Reply #2 on: July 04, 2008, 09:26:01 pm »

Thanks for your thoughts. Photomerge does the same distortion no matter which method is used. I see no reason for the program to distort one of the images - especially to do it on one end one time and then on the other end the other time - both images were lined up perfectly when shot, all the program has to do is merge them together - I've done that thousands of times before with no issues. I don't know if perhaps this is because these are p-45+ files - it has never done this with my p-45 files, nor with any other camera I've used. I get the same results with the same files on different computers, even when running standard PS vs. Extended (which should be the same anyway, but I tried it just as a control). I've never seen a command for the center of the photo - can't find any options really, other than choosing Auto, perspective, etc. I just checked and decided that the two different ways I was doing this was via auto, and then perspective. I tried doing it using cylindrical and it does work better - thanks for that. I've never had to do this in the past, ever - I wonder why? I wonder if it is because I normally do vertical shots and these are horizontal? Oh well, I'll keep plugging away - I've found photomerge to do a great job with this and have never found a seam anywhere (only issue is this funny distortion stuff of late)..
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BernardLanguillier

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Problem with Photomerge
« Reply #3 on: July 04, 2008, 09:43:12 pm »

It would appear that this was shot with a pretty wide lens, wasn't it?

I would tend to agree that what you are getting here is a normal result.

You might want to try more advanced pano packages like Autopano Pro or PTgui. They offer more projections options than PS does and would have no problem at all dealing with panos under 100 MPixels like this one.

Cheers,
Bernard

Panopeeper

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Problem with Photomerge
« Reply #4 on: July 04, 2008, 09:56:44 pm »

On the photomerge panel, select the "interactive layout" option; there are some controls there, I guess you can utilize them.

The warping you are seeing is very normal with the rectilinear projection; the shape/balancing depends on where you (or Photoshop) place the middle point.
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Gabor

ternst

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Problem with Photomerge
« Reply #5 on: July 04, 2008, 10:47:35 pm »

THANKS for the info guys!

Tim Ernst in Arkansas
« Last Edit: July 05, 2008, 08:03:04 am by ternst »
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Paul2660

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Problem with Photomerge
« Reply #6 on: July 05, 2008, 09:43:37 am »

Tim,

Which lens was that taken with? and did you do 2, 3 or more segments?  
As you found interactive mode will fix the issue, not sure what causes this.  I have found it to happen anytime I use Photomerge to stitch landscape oriented shots from the Phase.  

Paul C
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Paul Caldwell
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ternst

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Problem with Photomerge
« Reply #7 on: July 05, 2008, 10:19:39 am »

Paul:

Yes, same deal with me - I think it is the horizontal format that messes it up - don't have the issue when I do verticals, no matter what lens I use. As panopeeper suggested I just used the cylindrical tab and it worked fine (the final version above was five shots, but it looked exactly the same using just three of the shots, with 35mm lens). I don't recall having this issue with the normal back, just the plus back.
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Panopeeper

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Problem with Photomerge
« Reply #8 on: July 05, 2008, 11:33:58 am »

Quote
I think it is the horizontal format that messes it up - don't have the issue when I do verticals, no matter what lens I use
The "issues" are the very same, no matter in which orientation the frames are in the composition.

However, the degree of the "distortion" (which is none) depends on the angle of view and the projection. When you put a landscape oriented frame horizontally not in the center, then it has to be warped more than one in portrait orientation, because the former covers a wider area horizontally. The same with a wider lens.

The warping is particularly large with rectilinear projection far from the center. The reason, that the rectilinear projection is limited to a horizontal angle of 180° (of the total composition) is, that at that angle the vertical edges would have to be increased to infinity. In practice the limit is around 120-140°.

The rectilinear projection's result looks like a single shot with a rectilinear lense (as opposed to a fisheye). Imagine, how the scenery would look like at a very wide angle: objects at the edges appear smaller than in teh center. When you make separate shots with much smaller focal length, the frame depicting the "edge" covers a much smaller area than the edge of a single frame with large angle of view. Therefor the far edge has to be stretched - that's what you think of as "distortion".

The warping is linear with rectilinear projection, but it becomew curved with the other projections. For example with cylindrical projection the top and bottom edge of the frames have to be warped in barrel-like shape, the degree depending on the angle of view.

You may profit from going through following demonstrations, which I created just to explain some closely related subjects:

http://www.tawbaware.com/forum2/viewtopic....t=4700&start=12
http://forums.dpreview.com/forums/read.asp...essage=24047035
« Last Edit: July 05, 2008, 11:35:23 am by Panopeeper »
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Gabor

ternst

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Problem with Photomerge
« Reply #9 on: July 05, 2008, 11:44:55 am »

I still wonder why it would distort the image on the left one time, then distort the image on the right the next time, even though the exact same three images were used and all settings were the same? And why it would just distort a single image on one end and leave the other two alone? And why this never happens on vertical shots, no matter how wide the lens? Does really matter to me I guess now that I know I can just push the cylinder button and it will work perfectly! (I just want the stitch to work, not have to know why or how, nor do any of it manually - CS3 does such a terrific job with just one button - just gotta know which button.)
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NikoJorj

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Problem with Photomerge
« Reply #10 on: July 05, 2008, 05:22:05 pm »

Quote
I still wonder why it would distort the image on the left one time, then distort the image on the right the next time, even though the exact same three images were used and all settings were the same?
[a href=\"index.php?act=findpost&pid=205713\"][{POST_SNAPBACK}][/a]
It's because, unlike more advanced pano stitchers (PTGui is indeed very nice, Hugin is not that bad too, and there are plenty others), with photomerge you can't set the center of your image, ie the reference point for all the perspective conversions needed to stitch the pano. It is set automatically, and sometimes in a curious way, of course.

With cylindrical projection, the transformation is rather constant from one photo to another ; with rectilinear, it is proportional to the distance of the image center. hence the 'distorsions' (re-projections actually) you see here.
There still can be a perspective problem with the cylindrical projection : when photomerge doesn't have the same sense of horizon as you (and the world), happens generally when shooting handheld. Mild cases can be solved with the warp command( not very elegant though), more drastic ones simply need a proper sticher.

In a nutshell, I'm really glad Photomerge is there, because the CS3 version makes now a very good job in most cases, and that eases the workflow quite a bit. But if you want to take stitching seriously, you need a proper stitcher.
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Nicolas from Grenoble
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JeffKohn

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Problem with Photomerge
« Reply #11 on: July 06, 2008, 11:20:38 am »

I've found that resuls such as in the first post are quite common when using Photomerge with the Auto or Perspective options, it's just not a very good stitcher and aside from the warping it will also often leave errors at the seams. The only thing I use Photomerge for is the 'Reposition Images Only' when stitching shifted images (where the camera was not rotated and a projection is not needed). That's the one thing PS can do that the dedicated pano tools cannot (at least, not the more popular ones such as PTGui or Autopano Pro).
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Jeff Kohn
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ternst

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Problem with Photomerge
« Reply #12 on: July 06, 2008, 11:34:45 am »

I guess I've just been lucky or something since all of the stitches I've done with CS3 have been just fine - until these recent horizontal P-45+ files - and I've been printing them up to eight feet wide with no seams or artifacts - I take a pretty close look on screen and under the bright lights. And now using the cylinder route even the + files are great, so I'm a happy camper...
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BernardLanguillier

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Problem with Photomerge
« Reply #13 on: July 06, 2008, 11:49:30 am »

Quote
The only thing I use Photomerge for is the 'Reposition Images Only' when stitching shifted images (where the camera was not rotated and a projection is not needed). That's the one thing PS can do that the dedicated pano tools cannot (at least, not the more popular ones such as PTGui or Autopano Pro).
[{POST_SNAPBACK}][/a]

You might find the following link interesting:

[a href=\"http://www.ptgui.com/support.html#6_13]http://www.ptgui.com/support.html#6_13[/url]

I have never tried to use this for flat stitching, but it should probably work.

Otherwise, Realviz Stitcher can do that.

Cheers,
Bernard

SeanBK

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Problem with Photomerge
« Reply #14 on: July 08, 2008, 02:37:17 pm »

Quote
I guess I've just been lucky or something .......P-45+ files - and I've been printing them up to eight feet wide with no seams or artifacts - ....... even the + files are great, so I'm a happy camper...
[a href=\"index.php?act=findpost&pid=205945\"][{POST_SNAPBACK}][/a]
 Tim, I saw your site & the images are great. Looks like you are taking advantage of longer exposures by Phase backs. Your waterfall series what is longest you have used & which one? I hope you don't mind sharing that, as Hasselblad's back limits one with 32 secs, while Phase goes much higher, albeit noise increase, hence the question. Thanks
   Sean
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JeffKohn

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Problem with Photomerge
« Reply #15 on: July 08, 2008, 03:38:11 pm »

Quote
You might find the following link interesting:

http://www.ptgui.com/support.html#6_13

I have never tried to use this for flat stitching, but it should probably work.

Otherwise, Realviz Stitcher can do that.

Cheers,
Bernard
[a href=\"index.php?act=findpost&pid=205947\"][{POST_SNAPBACK}][/a]
Thanks, I'll give that a try. Looks like it could also be useful for aligning focus-bracketed images.
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Jeff Kohn
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BernardLanguillier

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Problem with Photomerge
« Reply #16 on: July 09, 2008, 12:22:09 am »

Quote
Thanks, I'll give that a try. Looks like it could also be useful for aligning focus-bracketed images.
[a href=\"index.php?act=findpost&pid=206476\"][{POST_SNAPBACK}][/a]

Yes, I have used it for that and it works well, but I believe that it could also be used to do flat stitching.

Regards,
Bernard

ternst

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Problem with Photomerge
« Reply #17 on: July 09, 2008, 07:26:02 am »

Sean:

Most of my waterfall images were taken in the 5-10 second range. Once in a while I will do one that requires an exposure of 30 seconds or longer, but that is rare. The Phase back does great with these times (no noise), but as one of the phase dealers noted here on another thread, the "one hour with no noise" claim by phase is simply false - in fact you can't get anywhere close to an hour "noise free" exposure, but I guess we have come to expect false advertising these days - what a shame. I would feel handicapped if I could only go to 32 seconds with my camera - is it true you can't do longer exposures even on bulb? Wow, I could not imagine...
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