Figure 1. Notion of quantal meta-surface inspired from analogue-to-digital conversion and image compression.

(a) Quantization of an analogue phase distribution with a uniform 2π-span and a fixed spatial resolution. (b) Lossy and (c) lossless compressions of figure (a) using wavelet transforms, with and without thresholding, respectively. In this example, the lossless alternative results (at first level) in a three branch tree to represent the structure of the decomposition; note here the spatial resolution doubles. Both, (b,c) contain less information and a smaller number of quanta—which are no longer uniformly distributed either spatially or in the phase domain.