WO2003027958A1 - Procedure for the selection of groups of colours in harmony belonging to a tintometric system - Google Patents

Abstract

A procedure for the selection of groups of colours in harmony belonging to a tintometric system comprises the preparation of means of selecting a range of colours defined by colorimetric coordinates, selection of a reference colour from this range of colours, and generation of a group of colorimetric coordinates which define one or more theoretical colours in harmony. The procedure also comprises conversion of the group of colorimetric coordinates into a corresponding group of parameters belonging to a tintometric system, which define one or more real colours.

Description

PROCEDURE FOR THE SELECTION OF GROUPS OF COLOURS IN HARMONY BELONGING TO A TINTOMETRIC SYSTEM

The invention relates to systems for the processing of colours, and in particular systems for the selection of groups of colours which are coordinated and in harmony. The invention has been developed with particular regard to a procedure which, when a reference colour belonging to a colorimetric space has been determined, is capable of selecting a group of respective colours, in harmony with said reference colour, belonging to a tintometric system.

There are numerous known colour selection systems capable of selecting one or more groups of colours which are in colorimetric harmony with a predetermined reference colour. These systems have been extensively developed in particular in the sector of computerized graphics, where an ever- increasing number of applications requires different colours to be generated and combined with each other. To facilitate this selection operation for users with little expertise in colour perception theory, there are various known solutions which envisage greater or lesser interaction on the part of the users. In some of these systems it is possible to produce numerous combinations by selecting each individual colour in turn, in others the selection of a group of colours in harmony with the reference colour selected is performed directly by a procedure implemented on a computer.

United States patent US 5,311,212, for example, illustrates a colour selection system in which a reference colour is parameterized in a uniform colorimetric space, such as for example the CIE 1976 space (L*a*b*) , and the generation of one or more groups of colours in harmony is performed by a procedure implemented on a computer. At the end of the procedure, the coordinates of the colours obtained with the harmony algorithm are converted directly into coordinates of the RGB reference system, which is a non-uniform device- dependent colorimetric space, and the corresponding colours are displayed on a screen. The adoption of a uniform colorimetric space illustrated in this patent refines the choice of the reference colours and improves the selection of the respective colours in harmony.

The known types of procedure are particularly effective for those electronic colour processing and management procedures in which the final objective is to generate a colour which can be displayed, on a screen for example.

In the sector of painting products, such as wall coatings, paints, enamels and inks, the colours which can actually be reproduced, which we shall call real colours since they result from a combination of compositions with defined chemical-physical characteristics, such as, for example, colouring pigments mixed with white, neutral or variously coloured bases, may not correspond to the colours, which for comparison we shall call theoretical, defined by coordinates in a colorimetric space of either uniform or non-uniform type. To assist in understanding this concept, fundamental to the invention, we shall give some definitions of the terms which will be used in the description which follows.

A uniform colorimetric space, a CIE space for example, but not limited to this, is a reference system capable of representing all colours visible to the human eye, including monochromatic radiation colours, with the points defined by three coordinates. A non-uniform colorimetric space, for example RGB or HSV, is a reference system capable of representing only a limited number of colours from among those visible to the human eye, and is generally used for operating electronic devices such as computer screens, for example . A tintometric system is a set comprising a plurality of chemical compositions such as colour pigments and bases, for example, each having specific chemical -physical characteristics. Each composition in a tintometric system can be identified by a least one identification parameter which distinguishes it unambiguously within the specific tintometric system.

By reference formula we mean a function defined in a tintometric system, that is to say a sequence of one or more parameters identifying the compositions of the tintometric system and a quantity parameter for each of them. In this way, each reference formula enables a wall coating or paint of a predetermined real colour to be reproduced by mixing the compositions identified by the identification parameters in the proportions indicated by each quantity parameter. Any real colour, which can be defined either by a reference formula defined in a tintometric system, or by the corresponding colorimetric coordinates of any one of the colorimetric spaces of known type, belongs to a set which will be referred to in what follows as a tintometric colour space .

From the above definitions it follows that, in the sector of painting products, the colours obtained as a result of processing colorimetric coordinates defined in any one of the colorimetric spaces of known type might not belong to a tintometric system and therefore might not be defined by a reference formula and thus might not be actually reproducible .

From this point of view, the known types of procedures and systems for the automatic selection of groups of colours which are coordinated and in harmony are scarcely satisfactory for the production of paints, varnishes and similar. The purpose of the invention is to provide a procedure capable of selecting a group of colours in harmony with respect to a predefined reference colour, in which such colours belong to a tintometric colour space, and are therefore associated with reference formulae which enable them to be actually produced.

Another purpose of the invention is to provide a procedure which can be used directly in combination with devices of known type for the production of wall coatings and/or paints, such as for example colour pigment dispensers which deliver defined quantities of pigments in a base product, in accordance with selected reference formulae. In this way, after a reference colour has been selected, it is possible at the end of the procedure according to the invention to obtain a group of wall coatings and/or paints in harmony with the colour selected.

In order to achieve the above aims, the subject of the invention is a procedure for the selection of groups of colours in harmony belonging to a tintometric system comprising the steps of preparing means for selecting a range of colours defined by colorimetric coordinates, selecting a reference colour from among said range of colours, and generating a group of colorimetric coordinates which define one or more theoretical colours, said coordinates being generated according to at least one predetermined colorimetric relation with the coordinates of the reference colour, characterized in that it also comprises the step of converting said group of colorimetric coordinates into a corresponding group of parameters belonging to a tintometric system, which define one or more real colours.

Other characteristics will become clear from the following detailed description of a preferred form of embodiment. According to one of the preferred forms of embodiment of the invention, the procedure may be implemented on a computer comprising a memory, a display unit or video screen and an input device such as a keyboard, mouse, joystick or similar. Optionally, the computer may be connected to a data network or to a telephone line or similar. In that case the user is able to display the colours, reference colours or generated colours in harmony via a display device which utilizes any one of the known reference systems, for example RGB or HSV, and is capable of selecting the reference colour by means of any one of the known types of input device, such as keyboard, mouse, joystick or similar.

The first step in the procedure comprises the choice of a reference colour from a range of colours . The range of colours may belong to a uniform colorimetric space defined for example by the L*a*b* coordinates, though not limited to these, or to a non-uniform colorimetric space or, equally well, to a tintometric colour space. To allow the user to display the range of colours from which to make the above selection, the colorimetric coordinates which define each colour in the range are converted into coordinates of the reference system used by the type of display device, for example the RGB coordinates of a monitor. In this way it is possible to select one of the colours displayed on the monitor by means of the input devices of the computer, such as a mouse, for example.

Numerous procedures are known capable of converting the colorimetric coordinates of different colorimetric spaces to and from each other, but a specific description of these goes beyond the purposes of the invention and will therefore not be considered in more detail.

After the desired reference colour has been selected, it is possible to select and/or key in a predetermined harmony function by means of which the colours in harmony with the reference colour can be computed. A harmony function comprises an algorithm which, on the basis of colorimetric coordinates defined in a predetermined reference system, preferably in a colorimetric space, is capable of selecting a group of further coordinates associated with the same number of colours according to a predetermined colorimetric relation. The algorithm may for example be a computing algorithm or, preferably an algorithm based on a reference table, or alternatively an intermediate form between these.

On the basis of the colorimetric coordinates and of the type of harmony function which have been keyed in, the algorithm computes a group of colorimetric coordinates corresponding to a group of colours which are coordinated and in harmony with the reference colour.

The colorimetric coordinates thus obtained are used as selection criteria to carry out a search within a predetermined tintometric system. The purpose of the search is to identify those real colours belonging to a tintometric system which are the same as or most similar to the theoretical colours supplied by the harmony algorithm. To effect this selection, every colour obtained from the algorithm is compared with the colours associated with the reference formulae, stored in forms, defined by the parameters belonging to the tintometric system.

In particular, a comparison is made between the colorimetric coordinates of the colours of the tintometric colour space, which may be stored in the computer, for example, though without being limited to this, and the colorimetric coordinates of each colour generated by the algorithm. The comparison is based on mathematical criteria of a minimum and preferably on a criterion of minimum distance between the colorimetric coordinates stored and those generated. At the conclusion of this step, the colours selected will therefore be real colours which can actually be reproduced, since they are defined by a reference formula which enables them to be produced within the specific tintometric system. Naturally the real colours selected in this way will be close to the theoretical ones proposed by the harmony algorithm in so far as the search area has a sufficient variety and richness of real colours, and therefore of reference formulae, stored.

The real colours in harmony selected from the tintometric colour space can therefore be displayed on the computer screen by means of a conversion of colorimetric coordinates such as the one described above, thus allowing the user to make the final choice of the desired colour. In addition, or alternatively, the reference formulae of the real colours in harmony selected from the tintometric colour space may be supplied directly to a known device, such as a colour pigment dispenser, for the production of wall coatings and/or paints corresponding to the real colours in harmony.

According to another particularly advantageous characteristic of the invention, it is also possible during the step of selecting the reference colour, to choose a sub- space of the tintometric colour space in which to carry out the search for the real colours corresponding to the theoretical colours in harmony. The selection of such a search area speeds up the step of selecting the group of colours in harmony and, above all, establishes a specific colorimetric area from which to make the selection. For example, where the reference colour is a colour belonging to a tintometric system, and is therefore already defined by a reference formula, the search area may coincide with the sub-space comprising said reference formula. This choice is determined by the fact that it is assumed that the real colours in harmony will be used in ambient conditions similar to the reference colour and must therefore have the same chemical and physical characteristics .

A further particularly advantageous characteristic of the invention comprises the possibility of associating a filter function with the search carried out within the tintometric system, so as to exclude from the search the reference colours and/or formulae which have defined characteristics. In other words, it is possible to key in one or more parameters which make it possible to change, according to one or more predetermined criteria, the group of real colours from which to select the colours defined by colorimetric coordinates which are in colorimetric correspondence with the coordinates of the theoretical colours. The parameters keyed in can equally well belong either to a tintometric colour space, and thus relate to colorimetric characteristics, or to a tintometric system, and thus relate to chemical or physical characteristics of the shade, such as its commercial characteristics, for example.

According to an alternative form of embodiment of the invention, after a group of colorimetric coordinates corresponding to a group of theoretical colours has been obtained from the harmony function, the real colours may be selected by a colour matching procedure. As previously illustrated, the colours belonging to a tintometric colour space are defined by coordinates of a colorimetric space and associated with a reference formula. In a procedure of colour matching, once the colorimetric coordinates are known of a colour which it is desired to reproduce physically with a wall coating and/or a paint, it is possible to go back to a reference formula for it by means of conversion functions implemented, for example, on a computer.

One of the main advantages of this form of embodiment is that of appreciably increasing the correspondence between the theoretical colours in harmony and the real colours in harmony and, optionally, enriching a tintometric system by being able where appropriate to store, at the end of the colour matching procedure, further reference formulae associated with colours defined by colorimetric coordinates.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of implementation may be widely varied with respect to the one described and illustrated, without thereby departing from the scope of the invention.

Claims

1. A procedure for the selection of groups of colours in harmony belonging to a tintometric system comprising the following steps in combination with each other: a) preparing means of selecting a range of colours defined by colorimetric coordinates; b) selecting a reference colour from said range of colours; and c) generating a group of colorimetric coordinates which define one or more theoretical colours, said coordinates being generated according to at least one predetermined colorimetric relation with the coordinates of the reference colour, characterized in that it also comprises the following step : d) converting said group of colorimetric coordinates into a corresponding group of parameters belonging to a tintometric system, which define one or more real colours.

2. A procedure according to claim 1, characterized in that the step of converting the group of colorimetric coordinates comprises the following steps: e) preparing a group of real colours defined as a function of parameters belonging to a tintometric system and of colorimetric coordinates; and f) selecting from within said group those real colours defined by colorimetric coordinates having the minimum relative distance from the colorimetric coordinates of the theoretical colours .

3. A procedure according to claim 2, characterized in that it also comprises the following step: g) changing, according to one or more predetermined criteria, the group of real colours from which to select the colours defined by colorimetric coordinates which are in colorimetric correspondence with the coordinates of the theoretical colours.

4. A procedure according to claim 3, characterized in that the group of functions which defines a group of real colours on the basis of parameters belonging to a tintometric system is organized and stored on an electronic medium.

5. A procedure according to claim 3, characterized in that the colours from which a reference colour is to be selected are defined by colorimetric coordinates of a uniform colour space .

6. A procedure according to claim 3, characterized in that the colours from which a reference colour is to be selected are defined by colorimetric coordinates of a non-uniform colour space.

7. A procedure according to claim 3, characterized in that the colours from which a reference colour is to be selected are defined as a function of parameters belonging to a tintometric system.