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# What's this?
This is a very simple pair of functions `pack` and `unpack` that accept a 3D
matrix and a binary mask of the same dimension. It will "compress" the matrix
by cutting away everything the is not part of a cuboid hull of the mask and
saves the original dimension and position in a structure.
It's intended to be used in larger arrays of arrays that contain masked brain
data (hence 3D) to reduce the memory footprint.
# Example
(see [doc/zipmask_example.m](doc/zipmask_example.m) )
First, we create a 20x20x20 cube and a spherical mask in the center:
```
d = 20;
m = rand(d, d, d);
mask = zeros(d, d, d);
c = ceil(d/2);
for x = 1:d
for y = 1:d
for z = 1:d
if (x - c)**2 + (y - c)**2 + (z - c)**2 <= 16
mask(x, y, z) = 1;
end
end
end
end
plot_lattice3D(m, mask, 'original matrix/mesh');
```
We cut out everything outside of the mask with `zipmask_pack()`:
```
s = zipmask_pack(m, mask);
plot_lattice3D(s.data, s.mask, 'compressed matrix/mesh');
```
And re-grow the small data with `zipmask_unpack()`:
```
[um, umask] = zipmask_unpack(s);
plot_lattice3D(um, umask, 'expanded matrix/mesh');
```
# Limitations
Only works in 3D for now.