Fig 7. Side and top views of our 3D-ellipsoidal fittings to all categorical boundary data in lsY space.

For each category, we considered all points bordering with its categorical neighbours, including the achromatic centre. The ellipsoids’ sizes and positions were calculated by minimizing the planar distances between the points and the ellipses generated by intersecting the 3D-ellipsoid with the six constant-Y (horizontal) planes described in the main text. The top view also includes the triangle formed by the monitor’s RGB phosphorous.