Gradients (off unless asked for) found a blurred or noisy linear gradient in
part or in pieces, with bands around it.
The areas that may be a gradient are tried largest first, and one that is a
gradient is grown over every pixel next to it whose colour is within 10 levels
of the gradient's there: the pixels noise put a little off, a soft rim, the
pieces noise cut off it.
Linear-gradient inputs with Gradients on, paths beside the gradient, before ->
after: blurred 3.0 -> 0.5 (6 Colors) and 55.5 -> 0.5 (High Fidelity Photo);
noisy 11.0 -> 0.5 and 23.5 -> 1.5; scanned 5.5 -> 3.0 and 46.5 -> 37.0; clean
and aliased as before; dE within 0.02. No gradient on any input that is flat
colour, with any preset (the harness fails if there is one).
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