Horizontal lines in final image are bowed? [Archive] - Nodal Ninja Forum

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jimjones3
08-30-2011, 08:32 PM
Hi:

I'm a newbie to the NN forums...sorry if this is posted to the wrong area, but hope the experts here can help!

I just got my NN3 MKII a week or so ago. I stumbled upon the "Camera and Lens Settings" page on the NN website and set up my gear (Nikon D300 with an 18-70mm DX lens), everything seemed to be great.

I did several pano shots inside a room in my house. When I stitched 3-4 of individual images together, it looked like I wanted it to. However, when I tried to create a pano out of more than about 4 individual images, I got a weird effect - the horizontal lines (like where the wall meets the ceiling or the floor) had a bowed effect to them. The lines bow "outward" - towards the top of the image for the wall/ceiling line, and towards the bottom for the wall/floor line. I hope this all makes sense...if it helps, I can recreate the images and post examples.

Anyway - I'm totally new to panos, but this isn't the way I expected it to work at all. Do I have incorrect expectations, or am I just doing something wrong in stitching the images together? I'm using Photoshop CS5, I selected the "Auto" option, and took all the defaults.

Thanks in advance for your help!

John Houghton
08-30-2011, 11:57 PM
The curved horizontals are simply a consequence of the layout (projection) chosen for the output panorama image. Using perspective layout (aka rectilinear, planar or flat), all straight lines are preserved, but stretching effects at the edges become noticeable when the field of view is increased above about 110 degrees. For larger fields of view you need to use either cylindrical or spherical (aka equirectangular) layouts, in which only vertical features and the horizon are preserved. All other straight line features become curved. See http://www.ptgui.com/man/projections.html . In your example, adding more images increased the field of view to an extent that the automatic layout selection process chose cylindrical or equirectangular as being the most appropriate.

John

Wim.Koornneef
08-31-2011, 01:04 AM
Hello Jim,

As John explained the curved lines in your stitched output are a result of the chosen projection and often visible when you view the panorama "flat" with an image viewer or as a print but as soon as the panorama is converted to an interactive panorama (f.e to a Flash panorama that you can view in your webbrowser) then all curved lines are gone and all looks fine just as you expected.

For stitching panoramas and converting them to interactive ones are several apps available, a lot of people are using PTGui and Pano2VR, both are not free.
If you are looking for a free app then Hugin is a good option.
Both PTGui and Hugin have options to use projections that produce less curved lines in images for print or flat display.

Success,
Wim

jimjones3
08-31-2011, 02:30 PM
Thanks John and Wim - this makes sense. I appreciate your advice.