preview and birdseye

[Casper Boemann]

In fact

Perhaps we should do the filter on the entire visible part of the image and 
replace the image with the preview.

That is: Live preview which is the future I guess (see eg office12)

We would need to do it in a thread but that is needed anyway
whenever the user has made a change to configuration and the previous preview 
has been completed and shown the new previw calculation is begun by the 
thread. If no conf changes we don't start a new preview calculation.

My algorithm still holds for birdseye and layer thumbnails
-- 
best regards / venlig hilsen
Casper Boemann