Celtic Gilt Knotwork

The Celtic variant z -> |Re(z^2)| + i Im(z^2) + c iterated over the parameter plane and framed on its whole main body. Folding after the square rather than before closes the boundary into interlaced bands, and the set stays exactly symmetric about the real axis, whose slice is exactly [-2, 1/4]. Hue follows the smooth escape count and luminance follows an exterior distance estimate from the exact real 2 by 2 Jacobian.