Capturing Colour

The earliest photographs were monochromatic (one colour). Photographic materials recorded the world in tones of grey, brown or blue, but they could not capture a full range of colour.

Hand-colouring, especially of portraits, became a common practice in the 1840s. Since then, artists have used a variety of means, including paints and dyes, to add colour by hand to the surface of black-and-white photographs.

Tinting, developed in the 19th century, was another method of adding colour. A tinted photograph has a single overall colour, like pale pink or blue. This is the result of dyes added to the photographic papers in the manufacturing process.

In the early years of photography, occasional experiments and accidents in the darkroom had produced colour images. But, they could not be made permanent. In 1861, Scottish physicist James Clerk Maxwell demonstrated a system that would begin to satisfy the public's demand for colour photographs.

Colour Addition
Colour Subtraction
Film and Prints
Digital

Colour Addition

Red, blue, and green are the primary colours of light. Maxwell showed that adding together these primary colours in different proportions makes any colour. He used three transparencies (slides) of the same scene, each taken through a filter of one of the primaries. He projected the transparencies one over the other, each through a filter of the same colour. The result was a full colour image.

Maxwell's process became known as colour addition. In the following years, many colour photographic processes based on adding together coloured light were developed. Colour addition is used to produce the different colours on television and video screens.

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Colour Subtraction

White light is a combination of all the colours in the spectrum. Only a light source like a light bulb or flame gives out its own distinct colour. All other objects appear to be coloured because, when white light falls on them, they absorb or subtract all of the colours in the spectrum except a single colour or mixture of colours that is reflected back to our eyes. Dyes, pigments, and paints work in this way. Forming colours like this is called colour subtraction.

Most modern colour photography systems are based on colour subtraction.

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Film and Prints

True colour photography became practically available to everyone with the appearance on the market of 35-mm Kodachrome film in the mid-1930s. This was the first of many chromogenic or colour-forming photographic processes.

Chromogenic films consist of a base and the emulsion (or coating). The emulsion contains numerous layers that control colour balance, as well as three separate layers that are each sensitive to either red, green, or blue light. The colours that make up the subject being photographed are recorded in the corresponding layers of film. Colour print materials also contain layers that respond to different colours. Silver halide particles are the light sensitive element in colour films and print materials.

A complicated developing process resulting in the creation of dye molecules transforms the film or print material into a coloured image. The red-sensitive layer of the film produces a cyan (blue-green) image layer. The green-sensitive layer produces a magenta image layer. The blue-sensitive layer produces a yellow image layer. These three image layers combine to form a full colour image.

The prints from commercial photo labs are chromogenic prints.

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Digital

The charge coupled device (CCD) in a digital camera converts light into digital signals called pixels. Together, the pixels form a digital representation of an image.

In a digital camera, the CCD captures colour by fitting permanent colour filters to individual pixels. The colour of each pixel is determined by the level of red, green, and blue present. For each pixel, the level of brightness for each colour is given a digital number expressed as one byte (8 bits) of information. In 24-bit colour depth, also called true colour, more than 16.7 million different colours are possible. This is more than the human eye can differentiate.

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