PanEdit Lite: Image Stitching

The AutoStitch Dialog

Once the original flat images in the correct order, and the range of azimuth angles spanned by the scene has been specified, it is time to combine the images together into a seamless panorama. The stitching process is controlled mainly from the AutoStitch dialog. This dialog can be opened and closed by clicking on the "Stitch" button in the upper left corner of the main window. Additional stitching controls are provided by the Image Edit window. The Image Edit window can be opened by double-clicking on the main window.

The AutoStitch dialog comes in two forms based on the "Align All Sides" or "Align Selected Seam" setting. When first opened, this dialog has the "Align All Sides" option selected, as shown below:

The AutoStitch dialog has two sets of image stitching controls:

Ideally, the stitching process can be accomplished using only the automated controls. The recommended procedure for using the automated controls is described below in the section on Automated Stitching. Additional information describing each of the automated controls is provided under Automated Controls.

Depending on the properties of the original images representing the panoramic scene, it may be necessary to fall back on the Manual Controls. The automated controls work best for images captured using a tripod and pan head. If the original images representing the panoramic scene were captured using a hand-held camera, it is likely that it will be necessary to use the manual controls to help out the stitching process. Various factors which can influence the success of the automated stitching process are presented under Stitching Problems.

In either case (manual or automatic), the stitching process in based on the seams between adjacent images, not the individual images. The pair of images sharing a specific seam are identified by the names of the "Right Image" (the image on the right side of the seam) and the "Left Image" (the image on the left side of the seam). When the "Align All Sides" option has been selected, the specified operations are performed on all pairs of adjacent images. When the "Align Selected Seam" option is selected, the specified operations are performed only for the seam shared by the "Right Image" and "Left Image".

Return to AutoStitch dialog (top).
Return to Panorama stitching tool.

Automated stitching

If the original flat images are suitably "well behaved", the following procedure can be used to stitch the original images into a panoramic scene. "Well-behaved" means the original images do not suffer from the defects identified under Stitching Problems. Such images are typically captured using a tripod and pan-head. If the original images were captured using a hand-held camera, one should apply some of the Manual Controls before using the procedure given below.

Automated stitching procedure

  1. Make sure the Align All Sides option is selected, the Search Range is set to "broad", and the Pattern Size is set to "Medium". These are the initial default settings.
  2. Click on the Start button and wait for stitching calculations to be completed. Because of the thoroughness of the alignment searching, this step is relatively slow. The panoramic image in the main window will be updated after handling each seam. This step also performs a rough balancing of exposures.
  3. Inspect all seams to make sure every pair of adjacent images is aligned satisfactorily. The alignment is not expected to be perfect, but each seam should be close to the correct alignment. If any seam remains far from the correct alignment, repeat the previous step. If repeated application of the "Broad Search" fails to bring all seams into a rough alignment, see the section on Manual Stitching Controls.
  4. Click on the Minimize Adjustments button on the lower right side.
  5. Change the Search Range to "Narrow".
  6. Click on the Start button and wait for stitching calculations to be completed. This step should be much faster than the "Broad Search" performed in the previous stitching calculations. The panoramic image in the main window will not be updated until the last seam is completed, so do not worry if no improvements are seen as each seam is completed.
  7. Check all seams again to make sure each seam has come much closer to a perfect alignment. If not, repeat the previous step until all seams are very close to perfect alignment. If every seam does not apporach a perfect alignment, go to the section on Stitching Problems.
  8. Click on "Minimize Adjustments" again. This should have very little effect.
  9. Set the Search Range to "Tweak", then click on the Start button to polish up the alighment. This should be very fast and may be repeated a couple times to ensure that no perceptible changes are occuring.

When these steps have been completed, each pair of adjacent images should be correctly aligned, as shown in the following example.

Unlike the preliminary panoramic image shown above, the panoramic scene shown at this point should not show any duplication of scenery across the seam between any pair of adjacent images. Each seam may still be apparent as a vertical line where a pair of original images meet. The subsequent steps of Exposure Balancing and Blending the Images should make the seams invisible.

If there are no problems with any of the seams, one may click on the "Stitch" button to close the Autostitch dialog, then continue with Exposure Balancing.

Notice that this image exhibits black "fillets" above and below the seams between adjacent images. These fillets can be removed by reducing the upper and lower field of view angles before saving the final panoramic image.

Return to AutoStitch dialog (top).
Return to Panorama stitching tool.

Stitching Problems

The automatic stitching function only works when two adjacent images provide overlapping representations of the same part of a scene. This function can fail under any of the following conditions:

  1. A pair of adjacent images do not overlap, so there is a gap between the adjacent images, or the amount of overlap is too small to identify any recognizable features.
  2. Something moved or changed in the area where two adjacent images overlap.

    People, animals, vehicles, clouds, waves, doors, etc. tend to move. If any such motion occurs in the area where two adjacent images overlap, it can be difficult to decide how to align the images. Likewise, changes to lighting conditions, flashing lights, television screens, and computer monitors can all result in inconsistencies between adjacent images.

  3. There are no uniquely recognizable features in the region of overlap between two adjacent images.

    For example, two images may overlap in a blank wall, or an area covered by a repeating pattern such as bricks, blocks, or latticework.

  4. The camera was not rotated about the nodal point of the lens.

    This is okay when there is nothing close to the camera. Rotating the camera about an axis not passing through the nodal point of the lens causes parallax errors which are most noticeable for objects close to the camera. These parallax errors make adjacent images inconsistent so they cannot be stitched seamlessly. In extreme cases, this can cause the automatic stitching algorithm to fail.

  5. The camera roll and tilt angles are large or change a lot from image to image.

    These conditions are most common with images captured with hand-held cameras. See the section on Manual Stitching Controls for more information about these conditions and what can be done anout them.

In some cases, such as when there is a gap between adjacent images, it may be impossible to produce a satisfactory panoramic image. Likewise, if there are objects very close to the camera, and the camera is not mounted on a tripod and pan-head, then the overlapping portions of adjacent images may be incompatible, and it will not be possible to form a seamless panoramic image. In other cases, it should be possible to align adjacent images using the Manual Controls. After using the Manual Controls, the image alignment can be improved using the Automatic Controls with the Search Range set to "Narrow" or "Tweak".

Return to AutoStitch dialog (top).
Return to Panorama stitching tool.
Last modified January 13, 2000.