Straightening horizontals in Panoramas

[Pete JF]

I was wondering if anyone has any Photoshop tips or tricks that would help in straightening the often tooo curved horizontals in panoramic images.

Im working on a series of architectural documents. The pano format (stitched) is perfect for what I'm doing. The only thing that's bothering me is the way the some of the structures and buildings are being curved in certain images.

I don't like the rectilinear format because it's not wide enough and if you push it to the max, the edges get that sort of "rushing" distortion.

I've had some luck with using the various transform options in PS..warp, distort etc..

I'm wondering if any of you have any tips or ideas as to taking this further. In most cases I just want to modify these curves..make them a little bit straighter.

I find that this phenom in the architectural setting starts to make the images become much more about process, as opposed to content.

[Jonathan Wienke]

I'm confused by "not wide enough". Rectilinear is mandatory if you want to keep all straight lines straight; if you want to widen your FOV, shoot more frames. I've shot 270° panoramas, and 360° circular stitches are possible. If your horizon is curved, either your tripod is not level, or your camera, or both. That's something fixed by better shooting technique, not PS fixes after the fact.

[Pete JF]

Yeah,

I'm not dealing with bad horizons and poor shooting technique, the camera is level and everything is fine, horizonwizen.

The thing Im talking about is the natural distortion that occurrs in a panorama from the need to take horizontal lines and make them bend The Rectilinear format works except that there is a nasty bit of distortion at the edges, rushing edges is how I like to describe it..it happens especially when you really push the limits of the FOV for a rectilinear pano. So i guess in the respect, it doesn't work for me.

Yeah Johnathan, I understand that you can go to 360..Im not interested in that. In fact, i find those 360 panos to be a bit tedious sometimes, unless there is something particularly compelling going on all round. The stuff Im working on is,the most part, less than 180. 180 would be one of the extreme examples.

I have had some luck making corrections in the facades of buildings..curved rooflines, curved windowlines etc. I'm not trying to rescue the entire image from curved lines, only certain elements where I feel that the building is being represented way wrong.

The  "wide enough" statement was meant to express what happens in a Rectilinear pano when you push it to it's useful limit. The edges distortion gets to be pretty bad and I don't like it. I find the curves to be more acceptable than the edge distortion.

What I am experiencing are delightful panoramas that have the typically bent horizontal lines.

And yep, I'm looking to Photoshop to fix some of this after the fact. In this case I'm asking PS to iron out a curve and edge it towards being more of a truth. It's a wonderful program for this and it does help me, occasionally, when my shooting technique is not up to par after a hamburger and 12 beers.

Like i said, I'm having some luck using marquis selections and the warp tool to straighten some roof lines and such...Im looking for a little bit more control and some additional ideas/tools/selection methods...

Crafty ways of making quiet corrections to specific areas where curves are bugging me.

[Jonathan Wienke]

If you're swiveling the camera between shots, selecting rectilinear lens type and cylindrical projection will minimize the edge distortion you're complaining of, but beyond that, what you're asking for simply isn't possible. It is mathematically impossible to capture a 180° FOV centered perpendicular to a street or fence and have the it remain completely straight throughout a flattened-out image. Rectilinear projection keeps lines straight, but you start to get a "stretched" look at the edges as you go past 90° FOV, and you can't go past 180°. Cylindrical projection solves the edge "stretch" distortion problem, but then straight lines going through a wide horizontal FOV become curved. You can display your cylindrical projection prints curved (the viewer is standing in the center of a cylinder with your print attached to the inside so that the print itself is warped to match the warp of the image); if that is not practical, your only option is to manually warp the image to suit your taste, which IMO is a waste of time. Beyond that, you're asking for an exemption to the laws of optics/physics. You can't take a 180° FOV and flatten it out into a panoramic print without unstraightening or stretching something somewhere.

Your "straightened" photo looks less natural than the "uncorrected" version; you forgot to straighten out the sidewalk/curb in front of the building. And you'll find that there is no way to do that and keep the image looking natural. My advice is to quit obsessing over something that is an intrinsic part of extremely wide FOV images. You'd be better off wishing for gravity or some other physical law to go away.

[Pete JF]

I understand all of this and I appreciate your attempt to educate me but I don't think you are reading carefully.

I am trying to do some very selective straightening.

I'm looking, in this thread, for more control with transformation tools etc...ways to warp specific horizontals without having the verticals move ..stuff like that. (the verticals sometimes move when warping because of human hand spasms, and im trying to see if there any PS users who have a better handle on things)
 
I'm not trying to change the laws of process possibilities here. I'm trying to just go in and select certain buildings, small areas and tweak a few things.

Your statement that it is waste of time might be correct if I was trying to warp the ENTIRE image, but Im not trying to do that and think

[Pete JF]

I didn't ask for a judgement on what I should obsess about, I have a wonderful assortment of obsessions that are very close to my heart : )

[Pete JF]

Hi all,

Have they made any changes to the transformation tools in PSCS3?

I wish there was some way to freeze certain control points in the warp tool. Does anyone know if any advances have been made in this department?

Thanks

[jnaneshwars]

I was wondering if anyone has any Photoshop tips or tricks that would help in straightening the often tooo curved horizontals in panoramic images.

Im working on a series of architectural documents. The pano format (stitched) is perfect for what I'm doing. The only thing that's bothering me is the way the some of the structures and buildings are being curved in certain images.

I don't like the rectilinear format because it's not wide enough and if you push it to the max, the edges get that sort of "rushing" distortion.

I've had some luck with using the various transform options in PS..warp, distort etc..

I'm wondering if any of you have any tips or ideas as to taking this further. In most cases I just want to modify these curves..make them a little bit straighter.

I find that this phenom in the architectural setting starts to make the images become much more about process, as opposed to content.
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Hi Pete,

As I was reading about your problem it prompted me to share my experience with distortion. I have used a Sigma 10-20mm wide angle lens which is the widest possible and is a very good lens. The problem is that the vertical structures tend to tilt towards the center. As you compose check your horizon and tilt the camera a little up towards the sky and the vertical structures tilt outwards. Tilt the camera keeping an eye on the tilt of the structures till you are satisfied. Generally it requires a very mild tilt of the camera. I have tried this and has given positive results.