a few images are missed. perhaps it helps if i scan line-wise and turn garbage collection off. or i can use a different acquisition method that stores buffers missed images
acquisition errors can not be prevented by linewise scanning
expose timestamp and imagenumber for grab results
with a partial computation one image is missed:
    0.02500104 0.02500104 0.02500104 0.02500104 0.02500104 0.02500104
     0.02500104 0.02500104 0.02500104 0.02500104 0.025001047 38.914654
(perhaps the garbage collector started)
implement extract_csf in c
generate the 3 fftwf plans just once
i got rid of a lot of consing:

28,999,072 bytes consed

mostly because i plan only once and i use a c implementation of extract.
the latter might actually not be necessary
store the fourierspace parts
there was a logic error in the code where i wanted to use multiple plans
get rid of warnings in run-several-s