[sajqmrwy] Avoiding the lace card

Code data into a rectangular array of black and white pixels with no 3x3 block entirely of the same color.

Dividing the area into 3x3 blocks, setting 8 bits exactly to data and 1 bit as "parity" to avoid same-colored blocks does not work: two 3x3 areas can overlap at a parity block corner.  Perhaps the parity bit can also signify whether the data is inverted.

No 2x2 block
No 5-pixel cross

Inspired by 2D barcodes like QR, which want to avoid vast fields of the same color.  This is probably a solved problem.