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).
Gradients (params `gradients`, a checkbox in the panel for Grayscale and Color;
off unless asked for): an area whose colour changes evenly along one direction
is traced as one path filled with a linear gradient, not as bands of flat colour.
Gradients are found before the palette is made, so no colour is spent on their
bands: a connected run of smoothly changing pixels is a gradient when a plane
fits each colour channel with all three sloping the same way, the colours along
that way are at most six stops with ramps between them, and painting them back
gives the area's own pixels. Flat colour, soft edges between flat colours and
shading that goes two ways are left as they were.
The harness gains two linear-gradient inputs with known lines and stops, and
measures whether each is found, the angle of its line and the colours of its ramp.
bflatastic