RISMEDIA, May 27, 2010—Soon after a recent glossary posting in RealTown’s “TourTalk” group (http://www.realtown.com/mike/groups/tourtalk/24562), a question was sent in from one of our friends at another virtual tour company asking about the difference between 2D and 3D stitching. This company has been and continues to be a leader in the virtual tour industry, so I thought that if they have questions about this, most other virtual tour enthusiasts probably do as well. That said, the topic of this TourTalk article will endeavor to explain these differences in a clear and concise manner. To do this, I have asked Justin Furmage, CEO of Property Panorama to chime in (as it was Justin who explained the difference to me in the first instance).
The history of image stitching
Image stitching (The process of combining multiple photographic images with overlapping fields of view to produce a segmented panorama or image) has continually evolved since its introduction in the late 1970’s (see http://encyclopedia.jrank.org/articles/pages/1095/Photographic-Virtual-Reality.html).
Image stitching found its beginnings in a DARPA funded project, with the creation of the technology that is now found in Google Street View and other similar technologies. In the mid 1990s, image stitching started to go main-stream, as it became more widely used by many commercial entities, especially in the real estate and travel industries.
During this time, a host of innovative companies, such as PhotoVista and bamboo.com for example, began making stitching software commercially available, thereby empowering real estate agents with the tools necessary to create their own virtual tours.
Anyone with an adequate amount of computer ‘know-how,’ proper training, and moderate photography skills, could now create virtual tours and post them to the Internet. The stitching technologies employed in these solutions use a stitching technology referred to as 2D-Stitching.
With 2D-Stitching technologies, great care must be taken when capturing the overlapping photographs that will be used. The person taking the photographs must either use a tripod, or meticulously pivot around the camera, being careful to keep the camera in the exact position between shots as it would be if a tripod were being used. If this is not done correctly, the resulting (stitched together) panorama will be quite flawed, leaving the person who took the photos to choose between returning to the location to take new photographs or using flawed, distorted images in their tours.
Utilizing 2-D Stitching to stitch images together is a meticulous process that is somewhat limited in its versatility. Because the 2-D Stitching method moves the photos back-and-forth horizontally, trying to find similarities in the images, and thereby identifying the best possible matching points to use when blending any two images being compared into one, it is necessary that the person taking the pictures use great care when capturing such photographs. To illustrate the way that 2-D Stitching works, try to visualize the following:
1) You have taken a series of photos, in order from left to right, these photos overlap by exactly 25% and were taken using an old-style Polaroid camera.
2) After printing each of these photos, you stand them upright on a level surface, next to each other, in order from left to right.
3) While holding the first (left-most) photo in the series in a fixed (unmoving) position, slide the left edge of the second photo in the series over the top of the right edge of the first photo.
4) Slide the second image progressively further over the first image until the exactly matching area (overlap area) on the second image is exactly above the same matching portion of the first image below it (in this example when the photos overlap one-another by 25%).
5) Repeat this with the rest of the photos in the series.
3-D Stitching is the latest advancement in stitching technologies and has advanced the field significantly by eliminating most of the photo-taking requirements associated with 2-D Stitching. Rather than simply moving the images in the series back-and-forth horizontally to find the best match, as is done with 2-D Stitching, in 3-D Stitching, all photographs in the series are moved in all directions, and also skewed, rotated, warped, resampled and moved in all possible locations, three dimensionally to find a perfect match between the images being stitched.
This eliminates the requirement that the person taking the photographs use a tripod, keep the camera in a fixed position, overlap any specific or pre-determined amount, keep the camera level, keep the same exposure between photographs and a host of other requirements inherent with 2-D Stitching technologies. In fact, 3-D Stitching technology can seamlessly stitch photographs that were taken while the person taking the photos is walking around the room, provided the photos overlap any amount at all.
Due to the greatly reduced requirements regarding photo-taking, 3-D Stitching technology is rapidly empowering more and more individuals to incorporate panoramic virtual tours into their arsenal of marketing tools. Real estate agents who previously thought that they simply did not have (or did not have the time to acquire) the photography skills necessary to create high quality virtual tours of their properties are making virtual tours with a degree of quality that previously would have been attainable only by hiring a professional photographer.
Mike Barnett is the chief information officer for PropertyPanorama.com. For more information, visit www.PropertyPanorama.com.
