Back in the day (around the 1900s), people used to colorize black and white photographs using a technique known as Autochrome Lumiere, which is an additive-color mosaic screen plate process. The medium uses a glass plate coated on one side with a random mosaic of microscopic grains (made from potatoes), which were dyed red-orange, green, and blue-violet, and act as a color filter.
Anfractuosity managed to get his hands on an Eizo B&W monitor, which he intended to use to view black and white photos, and wondered if he could replicate the Autochrome Lumiere process to produce a color image. To do so, he utilized a cheap USB microscope to take an image of the LCD display pixels and found each had four sub-pixel elements. He then used the image to create a red/green/blue PDF that measures 433.1mm x 324.8mm.
Anfractuosity went on to make three PDFs, with one where each element is represented by one pixel from the display, another represented by 2 x 2 pixels, and a third represented by 4 x 4 pixels. He eventually used the second PDF (2 x 2) to create a Bayer pattern printed on acetate film. The film was then positioned over the display to transform black and white images (in this case, the movie Up) into color, or semi-color at any rate.
His process works by taking a pixel from a color image, breaking it down into four grey elements, and then uses the acetate overlay to generate a color image. It’s not quite the same as the Autochrome Lumiere method, but it isn’t bad either.
For those interested, Anfractuosity provides a walkthrough of his Rainbow colorization method on his project blog.