How to make a 2D isotropic matrix:
m = value * ones(336,512); % You pick what you want "value" to be.
How to add zero pixels (i.e. nothing to add at all) to 336:
336
How to make a 3D isotropic matrix:
m3D = value * ones(336,512,112); % You pick what you want "value" to be.
