MULTIVERSE . Code Red, Green, Blue

Give a child a box of crayons and paper, and watch. A vast majority of children not only draw, or at least doodle, but they do so with multiple colours. Do humans have a predisposition to colour? It causes us significant discomfort when we close our eyes and imagine a world where our closest companions and familiar forms are without colour. So it is only natural that painters through the ages have had a predisposition to painting with multiple colours.

Wall paintings in ancient caves such as Lascaux in France and Altamira in Spain show that even prehistoric artists took considerable trouble to create and use colour.

In all tones: A variety of colours was readily available to artists by the Middle Ages and they painted with myriad hues, shades and tints — all produced by various ratios of different paints, fillers and binders. Jan van Eyck’s The Arnolfini Portrait (1434).

Fast-forward about 40,000 years and we are in the Middle Ages, by when humans had carefully collected materials of different colours, found methods to grind them into fine powders and made binders to allow the formation of paints as we know them today. Once a variety of colours was readily available to artists, they could not only paint with myriad hues, shades and tints — all produced by various ratios of different paints, fillers and binders — but also wonder about the production and emergence of colours.

Renaissance artists such as Leon Battista Alberti and Leonardo da Vinci were experimenting with the science of colours in the 1400s. Centuries later, Isaac Newton would bring colour firmly into the realm of science. A mix of theory and hypotheses ensued. While theories banked on imagination and mathematical technique, testing the hypotheses led to the use of precise measurement and fabrication techniques.

Photography became a standard affair a century after Newton’s death in 1727. Black-and-white images, formed by a variety of chemical techniques, became common in Europe. The domain of the realist painter — portraiture and landscape — had a new method to be explored with. Photography was fast, accurate and rapidly reproducible, precisely the attributes a newly industrialising society desired. Its popularity soared, but colour remained an elusive idea.

How could you reproduce all possible colours by mixing only a few? The question can be more precise. What is the minimum number of colours which, when mixed, can make up ‘any’ other colour? The answer — one we now take for granted — took artists and scientists centuries to arrive at: The colours red, green and blue when mixed appropriately can create an array of colours.

Colour photography arrived in the late 1800s in a method that was as visionary as it was cumbersome. Imagine you have taken three black-and-white photographs of the same static scene. But there is a trick. For the first image, you put a red filter — a piece of red glass that will only pass red light — and click the shutter. For the next, use a blue filter, and then one more with a green filter. You will be left with three black-and-white images — sheets of film with greyscale images imprinted on them. Now imagine that you have a device that can project the image of a film back onto a white wall. Think that you have devised an elaborate contraption by which the images from three projectors — with red, blue and green filters, respectively, in front of the lenses — are projected onto the same rectangular spot on the wall at the same time. Conceptually, this is what happened. The coloured image in front of the lens is broken up into RGB (red, green and blue) components and is mixed back together by the projection method.

This method, while cumbersome, was immediately adopted by the Russian photographer and polymath Sergey Prokudin-Gorsky, who produced the first known colour photographs documenting Russia and her neighbours. The colour film which enabled a single sheet of film to capture all colours in one go soon came into vogue. This was achieved by coating three different light-sensitive layers onto the plastic film. The layers responded to... you got it... red, green and blue light. Without such inventions, the continuous miniaturisation of photographic technologies, particularly colour, would not have been possible. It is why we have a photo-realistic documentation of the 20th century in colour, brought to life by colour films commercially produced by companies such as Kodak, Agfa and Fuji.

Is it possible to still miniaturise such a system? Digital cameras overcame the need to carry film rolls, but they still could not record colour since putting three independent RGB pixels, one below the other, was impractical. A three layer chip design would have too much light being blocked by the time it travelled to the last layer of pixels.

A Kodak engineer, Bryce Bayer, came up with the solution that is ubiquitous today. Imagine a grid of pixel — dots that make up your image. Bayer proposed that each pixel in every row be provided with microscopic colour filters running thus... RGGBRGGBRGGB... and so on. You would get a mottled black-and-white image where some pixels were filtered red, others green and blue. Bayer developed the first algorithms — mathematical methods coupled with computer programs — that could infer three layers of colour based on incomplete colour information. The result is a powerful tool that many photographers, artists and filmmakers use every day without realising that it produces ‘accurate’ colour because of mathematical wizardry, something that would have been considered voodoo even a century ago.

Santanu Chakraborty

Santanu Chakraborty is a Bengaluru-based engineer, scientist and photographer

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