How to Create Simple Panoramas
by Dana Yoerger
PERSIAN WAR SHIPWRECK SURVEY
|These images were produced using a
technique called mosaicking or photo stitching. Under simple conditions,
commercial software can be used to take a sequence of overlapping images
and turn them into a single, blended image. In these examples, a series
of pictures were taken while rotating the camera from one side to the other.
If you simply printed the images out and tried to paste them together, you would find that the pictures don’t really fit together, even if you were careful to simply rotate the camera about the vertical axis and kept it fixed in all the other axes (pitch, roll, and 3 dimensions of position). The lack of agreement is caused by a number of factors, most importantly the projection of the lens, the tilt of the camera, and lens distortions.Image stitching software can compensate for many of these factors and can also blend the images together, smoothing the boundaries between the pictures. The image below shows 3-images and the resulting panorama. On the images, you can see the registration flags used to connect the images. Also, if you look carefully at the mosaic you can see that the edges of each of the individual images have been warped to reflect the parameters of the lens and the tilt angle (these were determined in an earlier step that requires the user to match many points in two overlapping images). You can also see that I didn’t hold the camera level, look at the angle of the waterline, but the software corrected my error. The software can determine the connections automatically, but I have gotten better results by providing the flags manually.
These results can be achieved by amateur photographers with a little practice and the right software (this describes my circumstances pretty well). Better results are obtained if the camera is rotated carefully without changing the pitch (vertical tilt) or roll (keep the horizon level) and if the images overlap by about 25% or so. I produced these mosaics using a program called Panavue Image Assembler, which has really changed my picture-taking. You can download a demo from the web for free to see if it works for you (www.paravue.com). Last I checked it is available for Windoze only, unfortunately for you Mac-only folks. Their “Getting Started” section is worth going through even for someone who is allergic to following instructions. I have listed a few hints for using Panavue at the end of this document. I haven’t tried other available packages, but there are many available. Most digital cameras come with such software.
I should also point out that this is the simplest form of mosaicking or stitching. Commercial software will also allow you to make 360 degree “wrapped” images and even fully immersive images that are effectively mapped onto the inside of a sphere, in which case you can simulate looking in any direction to the side or up and down. You can find these kinds of images on web sites advertising real estate, resorts, and in web-based versions of encyclopedias.
On a related topic, recent research results are allowing images to be assembled automatically even in challenging environments like underwater. These techniques go far beyond the simple results shown here. They allow large areas of the seafloor from hundreds of images taken in a complex grid to be assembled automatically into a single image with very low distortion. Search the web for work by Hanumant Singh at the Woods Hole Oceanographic Institution and his colleagues Oscar Pizarro and Ryan Eustice and you will find some recent results. They recently published a very large mosaic of the Titanic in the National Geographic Magazine. I apologize for not providing any links here, but I am writing this at sea and for one of the few times in my life I don’t have an Internet connection!
June 23, 2005
Dana’s hints of using Panavue (I assembled this list so my friends will start making their own panoramas and will stop bugging me about it).
1) Everything I’m about to tell you is in the
Panavue Getting Started and Tutorial sections. But if you’re like
me you’ll just download the software and start playing with it.
Follow the next three steps and you might save some time.
2) When you take your pictures, keep the camera at a
constant tilt angle (it’s OK to tilt it up or down, just keep it
constant) and keep the horizon as level as you can (the software will
fix small errors, but if you roll the camera too much you won’t
end up with a rectangular strip). Get some good overlap (25% or so) between
images. Stand still and simply rotate the camera from one side to the
other. Don’t move other than the side-to-side rotation. Better:
use a tripod.
3) For a regular stitching project, always use the Lens
Wizard first. This involves selecting two or 3 images from the center
of your panorama and matching up a bunch of points (I think it’s
7 for the 2 image version). This lets Panavue figure out the lens parameters
and also the vertical tilt. You’ll get better results if you do
this before starting the stitching. Save the lens parameters when prompted.
I make a lens definition for each panorama.
4) When you start your Photo Stitching project, go to the Lens Selection page and pick out the lens you just made in the previous step. Then look in the Options page. Choose “Cylindrical” under type of projection. First try “automatic stitch (no flags)”, and run the mosaic (little running man icon on the top toolbar). If this works, you’re done! If you see flaws in the results from the automatic stitch option, you can go back to Options and select “manual stitch with 2 flags” and fix up any image pairs where you don’t like the match. You’ll see two flags linking each image pair. If you click on a flag, then zoom in (magnifier + button on the top tool bar), Panavue will zoom both images centered on the flag (just what you’d want it to do) so you can move the flags to unique features in each image. Choose flag points that are near the edges of the images and are spread top to bottom.
THE PROCESS OF MAKING A PANORAMA USING PANAVUE SOFTWARE