Colour

For many people first association with the idea of "colour" is usually its large subjectivity in description, evaluation, or in communication. Axiomatically thinking that everyone sees and describes his own vision of colour impression, there is obvious difficulty in specifying and agreeing on common statement for even two sides (and almost impossible for more) of the process of information exchange. Meanwhile, since the thirties of the last century, we have methods and tools for standardizing and enabling precise and objective description of the "colour", we can guess that only the initial limitations (cost of research equipment) narrowed the broad introduction to the common practice of these helpful tools. To this days “subjectivity theorem” mentioned previously cast a shadow on "colour" and the impossibility of its precise definition, hence the great popularity of all kinds of colour catalogues and atlases, which are tangible and physical assistance in trade and marketing of the paints, textiles and graphics/design areas. Easiness of use of sample-cards is due to their high standardization at the stage of production (printing), but they everyday use brings a certain danger, not always conscious to the user, associated with the conditions under which evaluation and comparison of the colour is carried out – certainly about the illumination. We come here to one of the three main factors involved in the process of perception of colour - light, without which it is difficult to talk about standardization of reproducible and objective assessment of the colour. The issue of lighting can be ignored to some extent in the case of self-luminous colours, that is, straightly speaking, coloured light sources (incandescent, LED, fluorescent, neon signs), while for object colours (i.e. coloured objects) lighting, under which we observe an object is crucial to the perceived colour. Here comes the third component of vision process, which is the receiver of radiation, mostly identified with the human eye. To sum up - the process of colour vision (both by humans and by measuring instruments) consist of the three components: lighting, object and receiver of visible radiation. On this basis it was decided to normalize the first and last element of the triad, i.e. lighting and receiver, to become finally possible objective and quantitative description of colour and to allow the exchange of data between users in remote locations often without having to exchange of physical samples (standards). Due to strong connection between colours and lighting the task of standardization of the colour assessment was took up by the International Commission on Illumination, (CIE - abbreviated from the French name of its own). According to the their recommendations CIE 1931, there were established so-called illuminants, standardized source of light, namely A, B and C. The first corresponds to a light bulb with a colour temperature of 2856K, the second suit to (according to contemporary knowledge) cloudless sky at noon on temp. 4874K, and finally the C source corresponding to the average daylight with colour temp. of 6774K. On the basis of Guild and Wright research in the twenties of the twentieth century, there was established so-called standard observer, corresponding to the average human eye sensitivity to stimuli in a narrow, 2º observation field. Additionally, in the sixties of the last century, based on research of Stiles and Burch and Speranskaya, there was established additional observer, corresponding to a wider field of view of 10°. Also there were introduced a new sets of illuminants: D (daylight) and F (fluorescent) series. Combining together mentioned standardized light and the observer we can make a quantitative description of the colour of the object or a light source, by integrating (in practice replaced by summing) the product of the triad of components resulting in a three numbers describing colour in an appropriate colour space (RGB, XYZ, L*a*b* or L*C*h*). We've got here once again confirmation of the three-dimensional nature of the colour phenomenon, any colour can be accurately described by a minimum of three parameters. One word of caution, there is impossible to get back any base parameter of colour, for example index of spectral reflectance on the basis of the final integral parameters (XYZ), we have here a one-way road - from the spectral parameters we could obtain the integral parameters, but there is no way back, from integrals to spectral, hence the difficulty or opportunity - the colour of the specific parameters we can made with completely different set of colourants. Turning to the colouring agents we can clearly say about the current primacy of synthetic dyes and pigments with a clear regression of natural materials. Advances in today's chemistry provide a wide range of means by which the colourist has the ability to solve colouring tasks sustainable, despite significant constraints on the part of environmental requirements (and pseudo-ecological), taking bans on the use of cadmium-based pigments for example. However, this does not diminish the responsibility colourist for the selection of the optimal solution, not only because of the colour effect, but primarily on a set of working parameters of coloured medium. Here, too, we see a role by offering technical support and around-colour services.