Equirectangular Photos

[Jeremy Lezin]

This is a very amateur question but aimed at those who understand this program.

If I import a 360 file into other stitchers, the resulting equirectangular photo looks 'normal,' in that vertical lines are vertical and the entire (room, for example) looks as if it was taken by a wide angle camera.    People in the frame are upright, etc.

When I import a photo into PT GUI and select the Equirectangular projection, I end up with this 'swirling S" pattern.   IOW, it is distorted and not presentable.   I'd like to figure out how to import, stitch and end up with a conventional ER photo.

If necessary, I can include files to show what I'm talking about.  But if there's a simple solution, as in "select this projection,' then that would be great.

Thanks in advance for your help.

[John Houghton]

On Thursday, June 17, 2021 at 11:42:50 PM UTC+1 jerem...@gmail.com wrote:

This is a very amateur question but aimed at those who understand this program.

If I import a 360 file into other stitchers, the resulting equirectangular photo looks 'normal,' in that vertical lines are vertical and the entire (room, for example) looks as if it was taken by a wide angle camera.    People in the frame are upright, etc.

If you import a 360x180 equirectangular image into PTGui and set the output panorama projection to "Spherical 360 x 180 Equirectangular"  from the Projection menu of the Panorama Editor, you will get the same view as you describe.  The equirectangular image should have pixel dimensions in the exact ratio 2:1 - e.g. 6000x3000.  This aspect ratio is recognised by PTGui as indicating a 360x180 equirectangular image, and results in the automatic setting of appropriate lens parameters  (lens type Equirectangular, angle of view 360) on the Lens Settings tab (accessible in Advanced mode).

The panorama projection and angle of view settings can also be found on the fly-out menu of the Panorama Editor window (click the "<" icon in the top right hand corner to pull out the panel).

 

When I import a photo into PT GUI and select the Equirectangular projection, I end up with this 'swirling S" pattern.   IOW, it is distorted and not presentable.   I'd like to figure out how to import, stitch and end up with a conventional ER photo.

Importing regular photos is basically the same, except you need to select the lens parameters appropriate to the camera and lens used.  For an ordinary camera image, the projection would be Rectilinear, and the horizontal angle of view can be entered directly if known, or PTGui can work it out from the focal length and the size of the camera's image sensor.  If present in the image's file, exif data may provide this basic information automatically.  Panorama images generated by PTGui can be imported back into PTGui by setting lens parameters matching the creation parameters.

John

[Erik Krause]

Am 18.06.2021 um 00:42 schrieb Jeremy Lezin:

> If I import a 360 file into other stitchers, the resulting equirectangular
> photo looks 'normal,' in that vertical lines are vertical and the entire
> (room, for example) looks as if it was taken by a wide angle camera.
> People in the frame are upright, etc.

A 360° image in equirectangular projection looks never like a
conventional wide angle photo. That is because you can't flatten a
sphere without distortion. However, the distortion might not be obvious
depending on the subject.

> When I import a photo into PT GUI and select the Equirectangular
> projection, I end up with this 'swirling S" pattern. IOW, it is distorted
> and not presentable. I'd like to figure out how to import, stitch and end
> up with a conventional ER photo.

Now that is a different problem. If you have a S-shaped horizon and
verticals are not vertical (in equirectangular projection) the panorama
simply is not level. In PTGui you can try to level it manually by
dragging or rotating it in the Panorama Editor, or you can try to have
it automatically levelled by using appropriate control points. There is
an excellent tutorial about that by John Houghton:
http://www.johnhpanos.com/levtut.htm
Also see the FAQ page https://www.ptgui.com/support.html
and the tutorials and video tutorials section on the ptgui page (under
"Learn")

If that doesn't answer your question, please describe exactly, step by
step, what you do to reproduce the problem.

--
Erik Krause
http://www.erik-krause.de

[John Houghton]

An important consideration when importing images concerns cropping, which can result in curved horizons and sloping verticals.  For a levelled panorama, having properly vertical verticals, the horizon will be flat and be positioned across the centre of the Panorama Editor window.  When panoramas are imported, PTGui assumes that the horizon will be so positioned  - half way up/down the image.  If the image has been cropped at some stage,  e.g. to remove empty black space or for artistic reasons, and this results in the horizon position being no longer at the vertical centre,  then steps should be taken to restore the horizon position by making adjustments to the vertical shift lens parameter after loading in the image.  It's worth doing this manually in the case of large adjustment being required, but minor adjustment can maybe achieved during subsequent processing by including the vertical shift parameter in the optimizations.

Note that panoramas can be cropped asymmetrically for output by using yellow crop bars dragged in from the edges of the Panorama Editor image frame.  This often results in the horizon position no longer running across the centre of the created panorama image. 

John