Registration for HDR image alignmentWritten by Paul Bourke
In the following two images, the second is to be aligned to the first. Sharp features are identified in the each image (blue guide lines in Photoshop), these form a polygon (red lines). The pixel positions are recorded for each of the 4 points. The second image is automatically warped so that the polygon in the second image becomes aligned with the polygon in the first image. Before alignment features in the second image were misaligned with respect to the first image by up to 50 pixels.
The result was registration of image features to at most a 2 pixel error (worst case) over 10,000 pixel image width over the whole image frame. Difference between images before and after the registration illustrated by subtracting the two original images and the registered images.. Note that one doesn't expect total black because these are taken with different exposure settings, the images were equalised before differencing to reduce this variation. The important feature is the lack of outlines in the differenced image after the registration.
More extreme example: test case