Recursive Gradients

The underlying idea is to generate the equivalent of an image with gradients and uniform in the RGB spectrum (like this RGB Gradient Sample), while also enforcing the uniqueness of its colours.

Outline of the approach:

1. Start with a single area comprising the whole image and all available colours assigned to it.
2. Split each area into two equally sized inner and an outer areas, with respect to the centre of the image. Reassign colours with a higher/lower red intensity respectively to the inner/outer area.
3. Split each area into two equally sized upper and lower areas. Reassign colours with a higher/lower green intensity respectively to the upper/lower area.
4. Split each area into two equally sized left and right areas. Reassign colours with a higher/lower blue intensity respectively to the right/left area.
5. Repeat from 2. until all areas are reduced to a pixel with a unique colour assigned to it.

Image Licence: Public Domain (CC0).