Colour Printing

The nineteenth century saw the flowering of colour printing. Until that time, nearly all the colour that appeared in books was applied by hand, but then several processes were developed for colour printing on a commercial scale. They all,rift gold like the Baxter prints and chromolithographs, entailed repeated printing in exact register of each colour that constituted the final picture, a laborious and expensive procedure. Technical progress in this field depended on a proper understanding of the theoretical background of the nature of colours and how they could be produced by mixing the three primary colours, red, blue, and yellow. Some progress was made in applying the three-colour theory to photography, and with that and the invention of the half-tone screen, the way was clear to convince the eye that it sees the range of colours in the original when what it really sees is a collection of dots of yellow, magenta (red) and cyan (blue) ink (known as process colours) of varying intensities. A fourth colour was added later—black, to give greater depth of tone. The first example of three-colour printing was exhibited by F.E.Ives at Philadelphia in 1885, and it became a practical proposition from 1892. It could be applied to any of the three printing processes. Four plates are made by photographing the coloured original four times through a halftone screen, using a different coloured filter each time—blue, green, red and yellow for printing successively in yellow, magenta,rift gold cyan and black ink. More recently, the orthodox process camera began to be replaced by more sophisticated equipment, that is, by the photoscanner. It was in 1937 that Alexander Murray working for Eastman Kodak built the first scanner, in which a scanning head picked up light from a coloured transparency and a photomultiplier converted this into electronic signals. From these, various kinds of output can be derived, according to the printing process. Laser light is now used to expose the output film.