DOWNSAMPLE

Resamples the image to be in line with the Nyquist-Shannon sampling theorem.
This operation should be performed before any bluring or denoising.  This
operation assumes that the point to point resolution of the microscope is
0.1 nm (can be modified by adjusting the d value in operations.downsample).

Pixel Size:
The size of each pixel in nanometers.

Nyquist:
The targer number of pixels per point to point resolution of the microscope.
According to the Nyquist-Shannon theorum, this should be between 2.3 and 3.
Lower numbers lead to more downsampling and a more "pixelated" image.