Patch for KCurve and KisPerChannelFilter

[Boudewijn Rempt]

On Mon, 23 Feb 2009, Дима Казаков wrote:

> Emm.. Can i read about that pyramid anywhere?

Basically, it would be a mipmap: http://en.wikipedia.org/wiki/Mipmap. That is,
there would exist besides the full version of the tile (or layer, or rendered
image), also a tile at 50%, 25% and perhaps even smaller. And you'd scale the
image from the nearest scale level, instead of always from 100%. For preview,
if the image is zoomed in (which is most of the case), you'd only filter the
50% or 25% -- only filtering the full image when the user presses apply,
in a background thread.

The reason for maintaining the pyrarmid is performance and quality. It's much
easier and faster to scale from 50% to 48% than from 100% to 48%.

> > where we could filter at the zoom level nearest to the actual zoom level.
> > That would be
> > one solution, sort of.
> 
> 
> Why do we need many thumbs? And why filtering the nearest one? Why not have
> only two layer representations: original and current zoom level? Zoomed copy
> could (?) be used by projection (keeping in mind interpolation).

We'd have to update the zoom cache every time the user zooms in or out for every
layer, while when using a pyramid, keeping the small versions up to date can be
done in a background thread.

> > What is present, but isn't used atm (because there was a big problem and I
> > have to redesign this class), is setting a region of interest on the
> > projection; this would mean that for preview, only the visible part of an
> > image is filtered, recomposited and redisplayed.
> 
> 
> I guess it's not very useful for filters as most of them work on the whole
> image (i don't speak about tools). In Krita1.6 we had an ability to see
> scaled down output of filter in it's dialog. I could add one more complaint
> about that=) It was quite bad :)

:-). Well, the idea is that if you have big image, at 100% zoom level, you don't
see much of the image. So, if we filter only the visible area for the preview,
it would be enough. Of course, there are complications, like scrolling (because
the filter dialog isn't modal and things like that.

Boudewijn