Notes for the execution of the recipes:

The 2 Lin/Gain recipes expect by default that the frames in the SOF file 
are exactly 2 pairs (1 ON, 1 OFF) per different DIT value.

The requirement to have pairs in the ON / FLAT frames is unavoidable. 

However, there is an option to provide a number of OFF / BIAS frames 
instead of pairs of them, which will be used to compute a MASTERBIAS 
(used in Lin computation). The 2 first raw frames will be used for Gain 
computation. In this case, the parameter --collapse must be TRUE, 
otherwise the recipe will complain.

To activate the autocorr computation, the parameter --autocorr must be 
TRUE. If cpl was not compiled with fftw3 support, the process will be
extremely slow.

If autocorr is active, there is another parameter --intermediate which 
can be set to TRUE. In this case, the correlation images, and the 
difference images on which the autocorrelation is computed will be 
stored as intermediate products.

The default expects images of 1024x1024. If maximum size is smaller, it 
is necessary to use the params urx, ury, etc... for interest regions, 
otherwise the recipe will fail.
