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Way back when I was at school, before colour photography became so common that black and white became in vogue again, I distinctly remember one of the teachers, it was either Mr Powel or more likely Mr Foister demonstrating something that has fascinated me ever since. How to realize the original colour of a scene from a black and white photograph. To demonstrate he reproduced identical copies of the image on three pieces of film, but whether they were positive or negative I couldn’t be sure. He then projected each with a different projector, one through a piece of blue film, one through green, and the other through red, all in register and there magically on the screen the black and white scene became, give or take a bit, coloured! I have been thinking for some time that it ought to be possible to simulate that same effect on a computer using red, green and blue channels and at long last I have got around to recreating the experiment, after all it ought to be so much easier now, with a powerful PC and some advanced software, shouldn’t it? Well no, it wasn’t. The colour didn’t turn out that great. Very similar to what my tutor achieved. Mainly bluish with, yes, a touch of green but little sign of any reds at all, as you can see above.
I got an e-mail from one Patrick Atherton explaining that it can be done if you use 3 negatives, each taken though a different filter, red/blue/green and then project them together, and the other problems. The brightness of each projector needs to be adjusted to produce whites that are pure, and not tinted. And that as the 3 projector lenses cannot be in exactly the same spot you get some trapezium distortion on the 3 pictures so parts of the picture will be out of alignment. This was one of the problems with early colour TV, dozens of internal adjustments to correct this white balance and alignment. Thanks Patrick.
Carrying out the trials on a PC immediately overcomes the trapezium distortion so that leaves the colour problem. The reference to television was apposite because the colours I achieved in initial trials were indeed reminiscent early colour TV experiments, but as I indicated last time I wasn’t finished yet. I had one more thing to try and that was playing with each individual colour channel, and Patrick was perhaps pointing me in the right direction. Using the greatly undervalued and misunderstood tool CURVES which can be found in all but the most basic image editors, I tried adjusting the intensity and tone of the channels, all at once and individually; and the white balance. I created some interesting effects but I did little better at achieving the original aim i.e. getting a colour image from the black & white original (negative or positive) for little effort. So, unless someone else knows better, I conclude that if you want to colour some of your B&Ws you’ll get the best results digitizing them and then tinting them, subtly, on your PC. People used to do it with inks. The finished effect was usually very tentative or garish. Now we can do similar digitally but, because we needn’t risk the original and we have an infinite range of colours, we can do it better. It can be especially effective with pictures of people, and if they were there and can remember the detail and colours, then those B&Ws take on a new life.
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