Align a stack of photos

There are occasions where it is necessary to align a set of otherwise identical pictures:

  • Aligning red, green and blue channels to correct chromatic aberration.
  • Aligning photos taken over a period of time to create a time-lapse movie.
  • Aligning bracketed shots to create a single HDR or contrast blended[*] image.
  • Aligning photos taken at different focus distances to merge into a single extended Depth of Field image.

Panorama tools is particularly useful for this process since it allows sub-pixel alignment and has a sophisticated lens correction model for applying distortion - Even photos taken years apart with different cameras can be aligned perfectly.

Most tools for HDR generation such as photomatix[*] have some level of automatic alignment, so this may be sufficient for most purposes. Otherwise the hdrprep[*] perl script automates the process described below:

Aligning with hugin

  • Create a few hundred control points between each pair of consecutive photos with the g key in the control point tab.
  • Fine tune all points (available in the Edit menu)
  • Delete any control points with a correlation less than 90% (i.e. open the control point list (F3 or the Show Control Points icon in the toolbar), press the select by distance button, enter -0.9, and hit the delete button).
  • Optimise positions (ctrl-T), select points by distance again but this time enter 0.2. Optimise again.
  • Adjust the field-of view in the stitching tab to something slightly smaller than the input size so there are no transparent edges.
  • Stitch to multiple TIFF format.