This Summer, I mentor to GSoC projects, one which concerns general purpose resampling (more precicely, resampling tasks which are not dominated by downsampling), and one which is tailored for resampling tasks in which good downsampling behavior is more important. Let me describe one aspect of how I intend to set each of them up which some people may find unusual. The point is to generate discussion now as opposed as "after the coding is done." ----------- Motivation: ----------- When downsampling, the best image alignment convention is "corner-based physical coordinates" (that is: image extent goes from 0 to N, first pixel center is at .5; another version of the same convention: image extent from -.5 to N-.5, first pixel center is at 0). For example, exact area box filtering, the simplest decent downsampler, works more naturally with this convention. When upsampling, the best image alignment convention is "center-based physical coordinates" (that is: image extent goes from 0 to N-1, first pixel center is at 0). For example, bilinear, the simplest decent upsampler, works more naturally with this convention. The convention is used inside the sampler to determine the "physical" location of the sampling point relative to the pixel centers of the input image. ----------------------------------------------------- What I plan to have Adam Turcotte and Eric Daoust do: ----------------------------------------------------- The "tuned for upsampling" method will use the "corner-based coordinates" convention (Adam), and the "tuned for downsampling" method will use the "center-based coordinates" convention (Eric). A side effect of this choice is that if one downsamples with one and upsamples with the other, the resulting image will not be aligned with the original. (Of course, if one uses the same resampler for both, the results will be aligned, unless the calling routine (e.g., scale) messes things up, which I think it won't.) In my opinion, this is a small price to pay. Nicolas Robidoux Universite Laurentienne _______________________________________________ Gegl-developer mailing list Gegl-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gegl-developer
