hjulenissen wrote:That may mean oddly shaped kernels that may be impossible to obtain using "tensor" methods?
This was the original reason for using a EWA for distortions. Also why it is not used for one of the polar distortions as the 'area' the source of a pixel covers is actually a circular arc and not an ellipse (de-polar distort method).
Though that does not mean a elliptical area is not a bad compromise, I just felt it was better not to bother using EWA in that situation, as the blurring near the center of the resulting image would be too sever.
However in resizing or scaling images, the saming area are either rectangles or circles. You have then three posibilities, tensor (2-pass orthogonal) weighted filters, and cylindical (radially weighted) filters. Resize does the first, distort does the second.
Nicholas and I are also considering another Area Weighting sampling method that is really more like a distorted 2-pass area resampling for distort. In a scaling distortion (resize type) situation this would directly devolve to the same result as a tensor 'resize', but in a single (less optimized) pass. In heavy distortions it would have a rhombus like sampling area.
For image scaling there is another group of possibilities. Single 'point' interpolation (not a interpolative filter) whcih produces heavy aliasing when educing image size, while interpolative filters default to this for enlargements. Or a Super-sampled variation (take many points, using a grid, disk, or some other sampling of the source area that contributes to the destination pixel).
And there is also a thrid posibility... forward mapped 'splating'. though that is used more for the display of 3D objects that has a sparse surface sampling, than 2D image distortions.
Just remember a resize is just a special restricted case of a normal image distortion, and as such all teh introductory explanations given in Image Distortions actually apply, even before you get into 'areas', 'super-sampling', or 'tensor filters'.
See General Distortion Techniques
And in final summary (the second last line in the above section)...
Remember however all resampling techniques are just methods for determining the color of each individual pixel