Nothing if :schema:knows protocol filters.
Every value has a min, average and maximum value.
If you do your function on these three possibilities,
eg1: "[xmin= 0, xavg=127, xmax=255] * [ymin=0, yavg=127, ymax=255] / 255" = [0, 63, 255]
eg2: "[xmin= 0, xavg=127, xmax=255] + [ymin=0, yavg=127...