Shade halves of cells (vertical or horizontal; four possible shadings of a cell) so each possible shading of a cell is represented twice in each row and column.
Each cell may contain, as clues, up to 4 small pearls that refer to the corner of the cell they're in. If that sub-cell space is surrounded on 3 sides by shaded space and is unshaded, it can be marked with an unshaded pearl; the converse applies for shaded pearls.
The board's edge counts as the opposite shading of what's being considered. (unfinished)
Numbers in cell quadrants can denote how many quarters are in the shaded/unshaded orthogonal region it's in. (unfinished)