Skip to content

About ColourWorker

Cameras are traditionally considered poor tools for recording colour accurately. The images below provide a simple illustration by comparing three photographs of the Mona Lisa. Although the subject matter is unique there are clearly visible variations in the reproduction of colour across the images (1).

The reason why cameras often reproduce colours poorly is that the colour of a surface depends on the way that it reflects light of different wavelengths. This reflectance spectrum can be quite complex as the adjacent graph illustrates by comparing reflectance spectra of human skin and a green leaf.

In general, the RGB signal that a camera uses to encode colour is too simple to properly represent the complex variations in reflectance spectra that can occur and this makes the accurate measurement of colour impossible.

Fortunately, many practical applications that involve colour measurement are concerned with quantifying colour variation across a group of related objects, such as ripening fruit, rather than measuring the colour or spectral reflectance of a large number of unrelated objects, such as skin and paints.

This has important implications because spectral variations in the way that related objects reflect light are much smaller than the general spectral variations in the way that all objects reflect light.

ColourWorker exploits the relative simplicity of distinguishing between related objects by optimally combining knowledge of the subject material with the relatively simple colour signal (RGB) provided by the camera. By simultaneously compensating for variations in the scene illumination and encoding characteristics of the camera ColourWorker is able to make accurate estimates of spectral reflectance and colour appearance regardless of the illumination conditions under which the photograph was taken or the type of camera used.

(1) The comparison of these three images is only intended to provide a very simple illustration of how colour can vary across different photographs of an identical subject. Without knowing precisely how these images originated we cannot be certain what causes the visible differences in reproduced colour.