How do you a create 360° panoramic image?
To create the images that are typically used in virtual tours there are two common approaches.
Single shot lens
One of the easiest and commonest methods is to use a single shot lens which can capture the complete room in one photograph. The field of view from these lenses is typically 360 x 240 degrees so only a small part of the ceiling (zenith) and floor (nadir) is missing from the image. The image can then be imported into the virtual tour software to create the tour experience. This is a great solution for people who want an easy to use system that makes it quick to produce a tour, for example estate agents who may have lots of properties they want to photograph and who only expect the tours to be used for a limited time period. The drawback is that image quality is limited by the optical system. Single shot lenses tend to use a mirror system so the sharpness and detail of the image is not as good as direct viewing through a lens. The other main drawback is that the exposure setting used by the camera will be an average for the whole scene. Whilst this creates an overall satisfactory effect, certain parts of the image will be incorrectly exposed. For example the windows are likely to be over exposed and appear as bright white areas. This can be a disadvantage if you want to show a nice view that a property has through its windows. Equally areas that are dark in a room may end up being undersexposed and the detail will be lost in the final tour.
Image from fisheye lens
Another method of creating panoramas is to use a very wide angle lens – normally a fish eye lens. To create the panorama you then need to take several shots at different rotations. A typical set up would involve taking 4 photogprahs, one each at 0, 90, 180, 270 degrees. These photographs are then stitched together using software to create a 360 x 360 image which can then be utilised for the virtual tour, you can see one of the images form the fish eye lens on the left. The advantage of this approach is that images are of an higher quality than the single shot approach allowing viewers of a virtual tour to see much more detail. Additionally the exposure can be altered to suit the subject matter being viewed and therefore you can avoid over and underexposed areas as described above. This allows you to show the spectacular views from the window and the details in the darker areas of a room.
The disadvantage with this approach is that it is more time consuming to create the panorama especially as multiple exposures may be needed to cope with the different lighting conditions. The end result does though create a high quality tour with excellent image quality which is ideal for use on a website where the tour is likely to remain in place for a considerable period of time, for example tours of hotels or businesses. See here to view a tour created by this method.