[Gegl-developer] Area filters

[David Gowers]

Hi Øyvind,

On Thu, Jun 26, 2008 at 10:01 PM, Øyvind Kolås <pippin at gimp.org> wrote:
> On Thu, Jun 26, 2008 at 12:05 PM, yahvuu <yahvuu at gmail.com> wrote:
>> Øyvind Kolås schrieb:
>>> Making the  blur filter assume the
>>> buffer abyss (the region outside the defined image) to be transparent
>>> and extend the defined region by the kernel radius gives what I expect
>>> as the result from blurring it, a rectangle with a fuzzy edge.
>>
>> GIMP allows to blur a layer without getting fuzzy edges.
>> How will GEGL serve this use case?
>
> Formulated like that, this is GIMPs problem not GEGLs problem, one way
> to achieve this is to crop the resulting image to the pre-extended
> extents, I suspect that the result on the edges by doing this, will be
> roughly equivalent to what you get in GIMP when blurring a
> layer/rectangular selection etc.
>
> Another option is to define a new operation that doesn't grow, that
> also encodes the edge/abyss behavior (I hve written som GEGL
> operations based on random sampling of the neighbourhood that discards
> the random sample if it falls outside the defined area and does
> another random one instead).
>
> Another option that hasn't been fully explored that might prove more
> fruitful is allowing GeglBuffers to define the abyss/edge behavior.
> Whether the abyss is transparent blank (or opaque black for no alpha)
> like it is now or it mirrors/extends pixel data.

I believe tiling/wrapping would be more useful than mirroring. Right
now, I know two applications, tiling and texturing, where tiled edge
behaviour would help;  Offhand, I cannot think of any way to employ
mirroring abyss behaviour at all. Are there any?

David