How people get to know which colour it is when they convert a black and white photo into coloured one?
In: Technology
Usually it’s an informed guess. How well-informed depends on if there are references available. Best-case scenario is that you have a color picture available of the same scene. Next best is that you have color references for some of the elements. And of course some things always have the same color anyway (blue sky, green grass, etc.). Also, the goal isn’t necessarily to get a faithful reconstruction of the original scene. Often it’s mainly done to bring more life to old footage – a heightened sense of realism. So while you do have to get some things right (e.g. the colors of objects that are familiar to people, or of things that matter to the story such as the color of a certain army’s uniforms), it doesn’t really matter if, say, you make the front door of a random house look green while it was actually blue. This process of educated guesswork is known as *colorization*.
Occasionally, you can reconstruct color perfectly because you’re dealing with black-and-white images that were originally converted from color images, and the original color signal has left certain tell-tale artifacts in the black-and-white results. E.g. quite a few old BBC shows (such as Doctor Who and Are you Being Served?) were broadcast in color but only recorded in black and white. Fortunately for us in the present, the color signal in the recording interfered with the luminance signal, causing a distortion phenomenon known as “dot crawl”, and these distortions can be (and have been) used to reconstruct the original colors. This is known as *color recovery* and is a different process from colorization.
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