Eli5: How do photo restoration artists know the supposed colors of greyscale images?

Question

Are the colors based purely on their assumptions/imagination, or do the greyscale images retain some sort of data that tells what color on what part?

In: 641

Answer 1

In the absence of independent evidence it is mostly supposition.

Another factor I have seen that can cause error in colorization is the difference between pancromatic and orthochromatic black and white film.

Orthochromatic film was used frequently in earlier times & while it gives striking images it is insensitive to red light while being quite sensitive to blue and violet.

Pancromatic film was less frequently used in earlier times and was more evenly sensitive to different colors

So, a colorist taking an orthochromatic print of an orthochromatic negative may color items in the scene that were mostly red far darker or assume a different color because they show as practically black. While coloring blue items in the scene as very light tone even though in reality they were a mid blue.