Extend blue noise dithering from 2D patterns to 4D patterns #71
Description
For each 4D pattern in primary sample space, currently only the first 2 dimensions have spatial blue noise dithering between pixels. Ideally the blue noise properties would be present across the whole 4D pattern. This shortcoming was identified after user testing and gathering feedback, with clearly sub-par results shown.
Z-Order dithering was tested, which does stratify across all 4 dimensions. However, this method is not progressive. First attempts to make the method progressive were not successful as these lead to a reduction in quality of the original sample pattern and its convergence rate within a pixel.
Based on this, we believe the best approach is to continue using a priori / offline optimization approach, but extend this to optimize across 4D. Given the additional constraints on the optimization process, it's expected that a naive approach will reduce the quality of the results for 2D. So further exploration is required.