Gradients left a radial gradient as bands. An area whose colour does not go
along one direction is now tried as a radial gradient: the middle is the common
middle of the circles its pixels of one tone lie on (three tones, which must
agree within 3 px), the stops are read outwards from it
(`TracedGradient::radial`; a radial gradient fill in the document).
Harness: a radial-gradient input with known middle and stops; a gradient counts
as found only if it is of the input's kind.
Radial input with Gradients on: found in all 7 drawings, 0 to 1 path beside it
(8 to 15 without); dE 2.69 -> 0.25 (6 Colors, clean), 0.80 -> 0.25 (High
Fidelity Photo). The linear inputs are as they are without this. No gradient on
any input that is flat colour.
4024db4a42