In working on an implementation of Exact Area Box Filtering (modified so it does well both upsampling, downsampling, and actually, for arbitrary warps), which is particularly well-suited for downsampling, I have determined that the sampler should receive the inverse of the Jacobian matrix from the (currently, affine) transformation that is calling it. This inverse need not be exact--it can be an approximation, though the more accurate the approximation, the better the results. The motivation for this modification is that future developments such as warps, perspective, and other transformations of the same type will also be able to rely on the new sampler and use it to maximal effect. I propose modifying each affine transformation's create_matrix () method to generate both the Jacobian and (an approximation of) the inverse Jacobian. In addition, I will need to expand the OpAffine struct to include an additional GeglMatrix3 (call it matrix_inverse or inverse_jacobian?) to store this data. Now, I will also require passing this new matrix to the sampler. This appears to necessitate a slight API change, though the pre-existing samplers will simply ignore this new information. This expansion encourages further development of methods that take advantage of this inverse Jacobian data and sets a framework for future transformations that may also want to pass inverse Jacobian data to samplers that use it. My question at the moment is: what is the best way to pass this data to the sampler? Note: Passing the Jacobian matrix itself may be better, but Nicolas is of the opinion that degenerate cases are easier to handle if the inverse is passed. Adam Turcotte _______________________________________________ Gegl-developer mailing list Gegl-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gegl-developer
