Decimate the signal after low-pass filetering

[chrisgorgo]

Since low-pass filtering changes the effective TR it might be worth decimating (downsampling) the output to save space. This can be performed (in one step together with low-pass filtering) by one of the following functions:

• https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.resample_poly.html (FIR based)
• https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.resample.html (FFT based)

Important: the output file header information needs to be updated with the new effective TR

[chrisgorgo]

Started a discussion on NeuroStars about potential drawbacks of such approach: https://neurostars.org/t/decimate-downsample-fmri-data-in-time-after-low-pass-filtering/1173

[chrisgorgo]

Downsampling can also be done independently of filtering with https://docs.scipy.org/doc/scipy-0.15.1/reference/generated/scipy.ndimage.interpolation.zoom.html (with prefilter=False).