Interesting article

[Boudewijn Rempt]

One of the problems Krita faces atm is efficiently working at multiple
zoom levels. And a general problem in paint apps is working in fine detail.
Some parts of a painting will have finer detail than other parts, so ideally,
you'd want to be able to vary the resolution of your image locally.

Traditionally, we'd use a lazy-update pyramid. This is how gegl (and Oyvind's
experiments with gegl) work. I have heard Photoshop does the same,
internally. Krita doesn't do that yet -- we're only now running into
the problem.

http://www.visgraf.impa.br/Data/RefBib/PS_PDF/rita-lvelho-02/rita-lvelho.pdf 
uses wavelets to achieve that. Cool read, but a bit maths-heavy. But given
that we've got a wavelets fan in our midst...

Boudewijn