How people get to know which colour it is when they convert a black and white photo into coloured one?
In: Technology
Partly research and partly guessing. Some elements may be obvious (brown wood, blue sky, skin tone, etc), some may be researched (most popular color of a certain year of car) and some is just a colorists’ choice.
Someone just converted an awesome pic from the 1900s from black/white to color and they explained in the comments that almost every gray corresponds with an actual color. But it’s not an exact science. It was really interesting to read. I think it was in r/pics.
I’ll try to find it.
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.
It is generally research and informed guesswork.
If you have the original negative and know what kind of black and white film it was then you can check against a colour response curve for that film which will give you some clues as to what a particular grey is likely to be – but this still involves a lot of guessing. Mainly it is by consulting other references, e.g. we know that leaves are green, certain street signs are red or blue, bricks are red, slates are grey etc.
There is one exception to this. If you have a black and white film of a video that was originally photographed in colour then there is a recently developed process that can restore the colour based on the existence of “chroma dots” in the black and white image. This technology is being used to [restore the colour to old TV shows](https://www.theguardian.com/technology/2008/dec/11/digital-video-restoration-dad-s-army).
There’s a famous film that was converted from b&w to color. And along the way, they colored Frank Sinatra’s eyes brown. In reality, Sinatra was famously nick-named “old blue-eyes” because of his blue eyes.
So part of the answer is that they guess.
Latest Answers