Angus Manwaring wrote:

[Interpolation versus enlarging analogue film]
The difference is that you are enlarging true detail when you blow up a
film image.

Only up to the point where the negative still holds additional
information and where the gear used does not go past it's limits.
Blowing up a 35mm film to 4m x 6m should widely surpass said
limits.

Interpolation is an algorithm's best guess as to what the
adjacent pixels are likely to be,

True if you use a single image --- but (nitpick) if you have
multiple, near-identical images, you can do, ah, interesting stuff
http://auricle.dyndns.org/ALE/gallery-auto/
Note that that eats lots of CPU time for larger images.

-Wolfgang