# Align a stack of photos

From PanoTools.org Wiki

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

- Start up a new hugin project for each series and load the images. Set the Field of View, lens parameters and projection type, ie. if your lens is a fisheye, set this for both the input and output projection.
- Create control points via the Photos tab. Align_image_stack is specialized for this task. But also Panomatic or Cpfind work for this use case.
- Select "Positions (y,p,r)" and "Optimise now!" in the Photos tab.
- If necessary, fine tune the control points in the Control Points tab and optimise again.
- In the fast panorama preview, the images will be on top of each other. Select "Move/Drag" and "Fit", then select "Crop" and "HDR Autocrop".
- In the Stitcher tab, select "Calculate Optimal Size", then deselect the default panorama outputs and select "No exposure correction, low dynamic range" in the "Remapped images" section. Select "Stitch!".

See a more detailed view of this article here.

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