What is Stitching?

Whether you use a specialist camera that creates super-large format images, or you use a more conventional 135 format camera and shoot lots of pictures, you will probably need to do some "stitching". "Stitching" refers to the technique of using a computer to merge images together to create a large image, preferably without it being at all noticeable that the generated image has been created by a computer.

"Conventional" cameras, panoramic cameras and parabolic mirrors

If you have a specialist panoramic camera you may want to use stitching software to stitch the ends of the panorama together and then you will be able to create a QuickTime VR movie or display your panoramic image in a viewer. However by far the most popular way of creating a panorama is to use a standard camera to shoot a sequence of images that you later stitch into a single large panorama using computer software. The advantage of the panoramic camera is that there is only one seam to stitch on, but panoramic cameras are expensive by comparison to standard cameras.

There is one alternative to stitching which is to use a mirror device that captures a full circle in one shot. It consists of a curved mirror that is mounted in front of the lens. You then point the camera straight up and take a picture: the mirror means that you take a circular picture of the scene all around the camera. The software that comes with this device allows you to extract a single panorama. Apart from the speed and simplicity of this solution, it means you can take pictures in locations where it would be difficult if not impossible to use anything else: such as a picture in a crowded concert where everyone is moving and therefore it would be unlikely that stitching software would achieve photo quality results.

An example...

The simplest example of stitching is a single row panoramic picture. Below is an example of what happens when a set of images (taken with a rectilinear lens) are stitched. The illustration left represents a set of 8 pictures taken by a photographer standing at point X turning his camera through a 360 degree sweep. The images shown to the right are in fact merely 5 from a set of 12 and therefore represent only 150 degrees.

 
Original images taken with rectilinear lens
 
Images warped during stitching - appears to create fisheye-like distortion
 
Images blended into final panorama

This is not as simple as the above illustration would make it appear. The software has to precisely warp the images so that they will align and can be seamlessly stitched together. The amount of warping required will vary depending on the lens used to take the pictures. Look at the above diagram: if I was to use a lens that could capture 180 degrees in one go I could use just three pictures, but the amount of warping required would be much greater. The reverse is also true, such as if I use a 100mm lens.

Spherical panoramas

A spherical panorama is one in which the vertical field-of-view is 180 degrees: therefore when this image is displayed in a suitable viewer you can look in all directions including straight up and straight down. When you look straight down you either see the tripod, or possibly the ground (depending on whether the photographer has bothered to edit out the tripod).

Different kinds of stitching in software

When looking for stitching software, you might need one or more of the following stitching capabilities:

  • mosaic - stitch multiple rows of pictures that were taken without rotating the camera around a single point, but with the camera kept perpendicular with the subject. For example: (i) in order to scan a large poster or a map, it is scanned in sections and re-assembled. But each image represents a flat image that merely requires alignment, not warping. (ii) in order to take a picture of a large building that does not fit in a single shot, the photographer shoots a grid of 3 x 3 shots standing in a single spot. Although in this case warping is required, the panning angle is likely to be small compared to a panorama.
  • panorama (single-row) - stitch a single row of pictures (created by rotating the camera around a single point in a flat plane, which is normally parallel with the horizon)
  • panorama (multi-row) - stitch multiple rows of pictures (created by rotating the camera around a single point in a flat plane but tilting or pitching the camera up and/or down so that for each row of pictures the lens is not necessarily parallel with the plane of rotation)
  • panorama (pano camera) - just stitch together the ends of a panoramic picture created with a panoramic camera
  • panorama (single shot) - extract an image taken using a parabolic mirror such as the BeHere system, Tateyama PAL360 mirror lens, Versacorp mirror lens, Egg mirror lens, or RemoteReality OneShot 360 mirror.
  • spherical panorama - stitch any number of pictures in such a way as to create a spherical panorama, the important distinction between this and single or multi-row panoramas is that the "poles" (i.e the very top and bottom of the image) must be stitched also so that the user can look straight up and down and see a smoothly blended image. Software capable of spherical panoramas will support either single or multi row panorama stitching, which in turn depends on the lenses supported.