Source image is a crop of A Sunday Afternoon on the Island of La Grande Jatte by Georges Seurat.
For each pixel in the source image, the algorithm uses a vantage-point tree to find the closest unused color in the Lab color space, and places it in the output. It iterates over the pixels based on their value in the 4096x4096 Bayer matrix, so the late "bad" pixels are evenly distributed across the image.
This image was produced by a 16-threaded version of this algorithm in 20 minutes.
