Gaussian Pyramid
Iterative (convolution with the same Gaussian and resizing) is conceptually similar to convolution with successively larger Gaussians.
The larger the Gaussian with which one convolves, the narrower the low pass filter effect.
(diagram)
Used a cell array to represent the pyramid.
Used built in Matlab functions such as imresize with 'bilinear' mode because it is good enough and decently invertible.
This is technically "wrong" for various reasons but good enough for government work.
fspecial was handy to create a Gaussian filter.