HowTo? Straighten bowed horizontal lines to be straight+slanted. PS Perspective Warp?

[l_d_allan]

I often use a 14mm uwa lens on a full frame for images like large grain elevators. When I have to get in close to the elevator, the panos end up bowed ("bulging")  and warped horizontally. I can get the vertical lines to be straight and vertical, but I have problems getting the horizontal lines like the roof and bottom to be a straight and slanted.

 

Here are some samples. First is a grain elevator where I’m able to get far enough away on a bridge to use one image, and a medium wide angle lens. It would be fine, except for power lines in front ... the bane of the urban panographer.

http://berean.zenfolio.com/p199715988/h32af2910#h32af2910

 

The next is the same grain elevator where I am not far away at all. The pano is comprised on 7 images with the 14mm (360 degrees FOV), in portrait mode:

http://berean.zenfolio.com/p199715988/h32af2910#h3013a600

 

The verticals are straight and vertical, but the roof line is bowed, and has a fish-eye appearance. I’d like to the get the roof-line to be straight and slanted.

 

I’ve used all the Projection choices in the Panorama Editor, but none seem to fix the bowed appearance. Cylindrical tends to be the least worst. I realize this is somewhat inherent with uwa panos.

 

Is there a way to correct this is in PTGui? If not, how about Photoshop, Lightroom, or ACR?

 

Is this something the new “Perspective Warp” in Photoshop CC is meant to address? I haven’t tried “Perspective Warp” yet, but thought I’d check with this forum.

[PTGui Support]

Hi Lynn,

You'd need to use rectilinear projection, see 5.1:
http://www.ptgui.com/support.html#5_1

Alternatively you could get the horizontal lines to be straight by using
one of the transverse projections, but this will bow the vertical lines.

Kind regards,

New House Internet Services BV
Joost Nieuwenhuijse

-----------------------------------------------
PTGui - Photo Stitching Software

www.ptgui.com
For support see: http://www.ptgui.com/faq/
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On 23/01/14 14:30, l_d_allan wrote:
> I often use a 14mm uwa lens on a full frame for images like large grain
> elevators. When I have to get in close to the elevator, the panos end up
> bowed ("bulging") and warped horizontally. I can get the vertical lines
> to be straight and vertical, but I have problems getting the
> horizontal lines like the roof and bottom to be a straight and slanted.
> Here are some samples. First is a grain elevator where I’m able to get
> far enough away on a bridge to use one image, and a medium wide angle
> lens. It would be fine, except for power lines in front ... the bane of
> the urban panographer.

> _http://berean.zenfolio.com/p199715988/h32af2910#h32af2910_

> The next is the same grain elevator where I am not far away at all. The
> pano is comprised on 7 images with the 14mm (360 degrees FOV), in
> portrait mode:

> _http://berean.zenfolio.com/p199715988/h32af2910#h3013a600_

> The verticals are straight and vertical, but the roof line is bowed, and
> has a fish-eye appearance. I’d like to the get the roof-line to be
> straight and slanted.
> I’ve used all the Projection choices in the Panorama Editor, but none
> seem to fix the bowed appearance. Cylindrical tends to be the least
> worst. I realize this is somewhat inherent with uwa panos.
> Is there a way to correct this is in PTGui? If not, how about Photoshop,
> Lightroom, or ACR?
> Is this something the new “Perspective Warp” in Photoshop CC is meant to
> address? I haven’t tried “Perspective Warp” yet, but thought I’d check
> with this forum.
>

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[John Houghton]

Lynn, In the 360 image, the building ranges across 147 degrees or so, which is way beyond what is reasonable for rectilinear projection even.  You might try specialist software like http://www.altostorm.com/corrector/ .  Otherwise it's not out of the question to remove the offending wires in the first image: http://ge.tt/2ui0Y5G1/v/0?c  - using Photoshop editing tools.

John

[l_d_allan]

On Thursday, January 23, 2014 11:27:48 AM UTC-7, John Houghton wrote:

In the 360 image, the building ranges across 147 degrees or so, which is way beyond what is reasonable for rectilinear projection even.

Agree. Rectilinear looks pretty distorted.  

Photoshop CC's "Perspective Warp" isn't helping much. Drat.

Photoshop's "Transform + Warp" allowed some interesting straightening.

I have been seeing some success with PS's "Adaptive Wide Angle" filter (AWA). If PS builds the pano, then it can do a LOT of line straightening.

With a small pano using a 24-105mm at 24mm and only a pair of images, AWA really works well to straighten the perspective lines going to the horizon. Those ends up being more or less bowed with PTGui. (Perhaps I am ignorant about how to straighten those lines?)

http://berean.zenfolio.com/awa

The first five images are the pair of 24mm images, and then stitched together in various ways.

With a Samyang 14mm with 4 to 7 images, and stitching by Photoshop, it gets very distorted. (next 11 images) 

I did attempt to use AWA, and it does seem to have potential. I've included screen shots at various steps while wrestling with AWA.

Which leads me to ask: Does PTGui have the equivalent of the AWA filter? If not, could this be a feature request?

Any chance the recently identified projection written about by Chang, Hu, Cheng, et'al might work well in this scenario?

 

[l_d_allan]

On Thursday, January 30, 2014 9:14:54 AM UTC-7, l_d_allan wrote:

With a small pano using a 24-105mm at 24mm and only a pair of images, AWA really works well to straighten the perspective lines going to the horizon. Those ends up being more or less bowed with PTGui. (Perhaps I am ignorant about how to straighten those lines?)

....

 

Which leads me to ask: Does PTGui have the equivalent of the AWA filter? If not, could this be a feature request?

Are the t3 (New Line) CP's intended to accomplish "straighten line" (not necessarily vertical or horizontal)? I've never used them, and they don't seem to do much ... but that may be inexperience on my part on how to use them. The documentation and tutorials I've looked at didn't seem to address the usage and purpose of the t3 CP's.

 

[Jim Watters]

You need to optimize with Panotools PTOptimizer for t3 point
They are useful for calculating abcde values.
The t3 points will try to make the lines straight in the output projection,
Panotools does not recognize all the projections that PTGui now offers.
T3 points are also good at aligning two pictures that have no feature except a
line going through them. like a power line or the corner of a wall or ceiling.

--
Jim Watters
http://photocreations.ca

[Rodrigo Alarcon]

Hi Jim,

Where can you get hold of Panotools and instructions for its installation and usage? I have tried using it in the past but always said that it could not optimise the equirectangle panorama so in the end I gave up as most of the time PTgui makes a good job at aligning, but some time you get a rogue pano. Also I don't know what are the different projection is there an explanation about them and what is the difference between them?, I normally just go for equirectangle to create a spherical panorama.

kind regards,

Rodrigo

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[John Houghton]

Rodrigo, You probably don't need the Panorama Tools package as such.  If you load into PTGui an equirectangular image and specify the lens type as equirectangular and with an apprpriate horizontal fov, you can use the default PTGui optimizer on it perfectly well - if that's what you want to do.  You may have to assign control points manually, though.  As Jim says, t3 points are not supported, but you can download the PTGui version of the Panotools optimizer from the PTGui web site, and that does support t3 points:

http://www.ptgui.com/panotools.html

As an example, I straightened a rainbow in a (partial) equirectangular image using a row of t3 points spread along its length:

http://www.johnhpanos.com/bow-straighten.jpg

You just assign pairs of t3 points NOT on identical features but along a feature that would be expected to be straight when correctly rendered in the selected output projection.  PTOptimizer will attempt to position the panorama on the spherical stitching surface such as to bring the feature into a straight line in the output area.  If you have more than one line feature to straighten, use t4 points on the second line, then t5 points on yet another, etc.

John

[PTGui Support]

Just keep in mind that t3 points are not a magical way to get straight
lines in a 360 degree panorama. In all 360 degree projections only
vertical lines and the horizon line remain straight, all other lines
will be curved. Control points cannot change that.

Joost

> <jwat...@photocreations.ca <javascript:>> wrote:
> On 2014-01-30 12:25 PM, l_d_allan wrote:
> > On Thursday, January 30, 2014 9:14:54 AM UTC-7, l_d_allan wrote:
> >
> > Are the t3 (New Line) CP's intended to accomplish "straighten
> line" (not
> > necessarily vertical or horizontal)? I've never used them, and
> they don't seem
> > to do much ... but that may be inexperience on my part on how to
> use them. The
> > documentation and tutorials I've looked at didn't seem to address
> the usage
> > and purpose of the t3 CP's.
> You need to optimize with Panotools PTOptimizer for t3 point
> They are useful for calculating abcde values.
> The t3 points will try to make the lines straight in the output
> projection,
> Panotools does not recognize all the projections that PTGui now offers.
> T3 points are also good at aligning two pictures that have no
> feature except a
> line going through them. like a power line or the corner of a wall
> or ceiling.
>
> --
> Jim Watters

> http://photocreations.ca <http://photocreations.ca/>

>
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[Roger Williams]

I think I misunderstood the purpose of t3 points, which is probably why I've never had them work properly for me.

I thought they were to make lines straight when the panorama was viewed in a proper VR viewer. Isn't that so?
I know better than to try to make any old line straight in the equirectangular projection.

Roger W.

[John Houghton]

On Friday, January 31, 2014 8:19:11 AM UTC, Roger wrote:

I think I misunderstood the purpose of t3 points, which is probably why I've never had them work properly for me.

I thought they were to make lines straight when the panorama was viewed in a proper VR viewer. Isn't that so?

No, that isn't so.  t3 points are used simply to identify features that ought to lie along the same straight line in the output panorama image. One classic use is for seascapes where you have some overlapping images that have no stationary features for control points - just moving waves on the surface of the sea, To get the images aligned with no visible glitches along the (straight) line of the horizon, you can sprinkle t3 points along the horizon in each image and the optimizer will align them perfectly, and also correct any tendency to bowing in the images due to barrel distortion at the same time.  Of course you would need to fix the horizontal positions by inputting known nominal yaw values if there is not even one common feature present (like a rock or buoy) to take an ordinary control point.  

And there can be straight line features in the output panorama image that are NOT straight in the real world.  Take a look at the levelled panorama image in my post to Bob's  thread: "Help with panorama".  The circular frieze below the dome is rendered  as a straight feature in the levelled equirectangular image, but wavy when the image is not levelled.  So you could use t3 points along that line to level the panorama (but there's no shortage of vertical features for t1 points in that case).

John  

[l_d_allan]

On Thursday, January 23, 2014 8:03:44 AM UTC-7, PTGui Support wrote:

You'd need to use rectilinear projection

I've rarely used the Rectilinear projection, and hadn't been aware of the options for vertical and horizontal compression. I think it might work well for some of the smaller panos (under 120 degrees FOV) as a good alternative to PS's Adaptive Wide Angle.

My impression had been that Rectilinear was primarily for virtual tours ... about which I am also mostly uninformed.