¥LCT schema in use today have one
central idea: proper motions of features
in 2 successive images - whether G-band filtergrams, Ha images,
or photospheric magnetograms - separated in time by Dt are found by
maximizing a cross-correlation function, or minimizing an error function
between sub-regions of the images. The concept is generally attributed
to November & Simon (1988).
¥The FLCT method (which we developed) is
similar. For each pixel, we:
Ðmultiply each of the 2 images to be
correlated by a Gaussian, of width s, centered at that pixel; crop the
resulting altered images 1 and 2 by
chopping the insignficant parts of
the images;
Ðcompute the cross-correlation function
between the two cropped images
using standard Fast Fourier Transform (FFT) techniques;
Ðuse cubic-convolution interpolation to
find the shifts in x and y that maximize
the cross-correlation function to one of two precisions (chosen
by the user), either 0.1 or 0.02 pixel; and
Ðuse the shifts in x and y and Dt between images to find the intensity features'
apparent motion along the solar surface.