On 10/17/06, Daniel Rogers <daniel@xxxxxxxxxxxxxxxxx> wrote:
I think you are mixing up interpolation and resampling. They are
similar (abstractly anyway), but separate operations.
My claim is that interpolation and decimation both are resampling
operations, and thus shuld be grouped together.
Geert's interpolation API is sufficient. Interpolation rarely takes or
needs more than 16 pixels. A rescaling API needs to be able to declare
the size of the neighborhood around the pixel (an interpolation API
could probably use this). They probably both need another object for
extending the region at the edges (copy, reflect, zeros, wrap, etc).
As I see it this needs to be handled by the buffer implementation and
not the resamplers, each operation will only operate on a smaller
region of the image any abyss behavior should already be applied to
the data outside when data is mapped from storage to a linear buffer
to be operated on. (currently the behavior is always zeroed out data)
Both these operations are similar in that they need a neighborhood and
produce a new value based on that neighborhood, but mathematicaly they
are acomplishing two very different goals. Interpolation doesn't affect
resolution and is used for shifting and scaling up. Resampling is for
downsampling (aka decimating) a signal and is a type of anti-aliasing.
They are used in very different cases, and should probably have
different interfaces to reflect that.
Both scaling up and scaling down is resampling, changing the spatial
sampling rate of the image raster. Increasing the samling rate is
interpolation, decreasing it is decimation, both of them are
resampling.
One place in the GIMP code where these are used is the transformation
tools, the transformation code in GIMP uses a matrix to represent the
entire transformation. In the case of a perspective transform you need
to do both interpolation and decimation with the same resampler. What
I was suggesting is to keep the same cache of pixels available both
for the interpolation and decimation and use different functions for
retrieving the data.
/OEyvind K.
--
«The future is already here. It's just not very evenly distributed»
-- William Gibson
http://pippin.gimp.org/ http://ffii.org/
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