The canvas is split into squares, with uniform surrounding space to form a grid. Each square is filled with concentric circles, but the rendering is offset to avoid the centre of the circle. Rotation and some scaling is applied to offer variation.

Features:

Granularity - a larger granularity means smaller sections of circle and stripes of a larger width. There is still a chance of small lines within a grid, but they become less likely as granularity increases.

Grid size - The number of squares. Mid-range values are more likely.

Grid lines - These can be black or white, with equal probability. A complementary drop-shadow is also selected.

Grid spacing - The distance between individual squares.