WO2009121620A1

WO2009121620A1 - Conversion of color information for activating a light source

Info

Publication number: WO2009121620A1
Application number: PCT/EP2009/002470
Authority: WO
Inventors: Kenneth Martin
Original assignee: Ledon Lighting Gmbh
Priority date: 2008-04-03
Filing date: 2009-04-03
Publication date: 2009-10-08
Also published as: EP2260678A1; DE102008017072A1; EP2260678B1; ATE524051T1

Abstract

The invention relates to a method for converting color information for activating a light source, wherein color information is transferred from a first color space (R1) into a second, larger color space (R2) using a coordinate system (S) which represents colors. According to the invention, two different color locations (f1, f2), which lie in the coordinate system (S) on a straight line (g) running through a central point (z), are displaced relative to the central point (z) nonlinearly along the straight line (g) to transfer the color information. In this manner, a transformation of the color spaces can be achieved while maintaining the color tones. Furthermore, through the nonlinear shift, there is only a relatively small color change in a central whitish area about the central point (z), so that the danger is reduced of obtaining a color location which has a significant color from a color location which is "whitish" originally, that is before the transfer.

Description

Implementation of color information for the control of a light source

The invention relates to a method for converting color information for driving a light source, wherein a color information is transmitted from a first color space into a second, larger color space using a coordinate system representing colors.

If certain color effects or color sequences are to be generated with a light source, for example an LED light (LED: light-emitting diode), the corresponding color information generally has to be generated as a prerequisite for a corresponding activation of the light source. This is usually done by means of a liquid crystal display (LCD) - also referred to below as a "display" for short - with the fundamental problem that in general the amount of all the colors which can be produced with such a display is In the case of common LED lights, which can produce colored light, it is generally true that not all the colors that are produced by the luminaire are different from the set of all possible colors of the light that can be produced with the light source in question can also be generated on the display.

To specify a certain amount of colors, there are different possibilities; For example, for this purpose, the known so-called CIE standard color chart (CIE: Commission Internationale de l'eclairage) can be used. This is a two-dimensional coordinate system for

Representation of colors, wherein the different colors lie within an approximately horseshoe-shaped area; on the abscissa x-coordinates of color locations are plotted, on the ordinate the corresponding y-coordinates. In Fig. 2, the CIE standard color chart is schematically sketched. (Please note that due to the given conditions no color representation is possible, therefore it should be remembered that blue shades are to be found in the lower left area of the "horseshoe", greenish hues in the upper area, red hues in the area of the right corner and there are yellow shades between the green and red areas, and in a central area of the horseshoe there is a whitish area.)

Furthermore, the three color loci R, G, B of the known sRGB color model (sRGB: standard RGB) are sketched in FIG. 2, which is usually used in displays (color locus R in the red region with x = 0.64, y = 0, 33, color locus G in the green area with x = 0.30, y = 0.60 and color locus B in the blue area with x = 0.15, y = 0.06). As is known, by mixing the corresponding three colors R, G, B, all the colors which lie within a triangle whose vertices correspond to the color loci R, G, B can be produced; in Fig. 2, this triangle is also shown.

In the following, the amount of all the colors that are within a certain range in the standard color chart or generally in a color chart will be referred to as "color space." The color space formed by the three named color loci R, G, B will be referred to as "sRGB color space". designated; In Fig. 2, the sRGB color space is designated by the reference Rl.

A light source with which light can be generated in different colors usually has a plurality of bulbs, each of which can emit light of a particular color. By appropriately differently weighted control of the lamps can produce light of different colors with such a light source. All colors that can be generated in this way are thus again in the representation of the CIE standard color chart within a polygon whose vertices exactly correspond to the coordinates of the colors in which the individual light sources of the light source can emit light. In FIG. 2, a triangle E1, E2, E3 is shown by way of example for such a polygon. Accordingly, the amount of colors limited by this triangle will hereinafter be referred to as "light source color space" R2.

It can be seen that in the schematically illustrated example, the light source color space R2 is larger than the sRGB color space Rl.

To convert color information from the sRGB color space Rl into the light source color space R2, it could be provided that the colors of the sRGB color space Rl be transferred with their x and y coordinates of the standard color table 1: 1 into the light source color space R2. However, this would mean that the possibilities of the light source to produce light of certain colors are far from fully utilized.

Alternatively, the sRGB color space Rl could be transformed into the light source color space R2 such that the vertices R, G, B of the sRGB color space Rl coincide with the vertices El, E2, E3 of the light source color space R2. This is indicated in Fig. 3 with corresponding dotted arrows. However, this would mean that shades move. For example, it can be seen that with such a procedure the color locus G is transferred or transformed into the color locus E2, and therefore this transformation from a more yellowish green creates a much darker green.

The invention is based on the object to provide an alternative method for the implementation of color information for controlling a light source; In particular, the color display options of the light source should thus be able to be utilized as much as possible.

This object is achieved according to the invention with the objects mentioned in the independent claims. Particular embodiments of the invention are indicated in the dependent claims.

According to the invention, a method for converting color information to control a light source is provided, wherein a color information is transmitted from a first color space into a second, larger color space using a coordinate system representing colors. In order to transmit the color information, two different color locations, which lie in the coordinate system on a straight line passing through a central point, are displaced along the straight line with respect to the central point in a non-linear manner.

Thus, nonlinear stretching is performed with respect to the central point.

By moving the color loci along a straight line that runs through a central point, it is possible to achieve that the hue or hue of a color locus does not change during the displacement or transformation. It is thus possible to implement color information in which the shades are preserved. Further, by having two different color loci lying on such a straight line shifted in a non-linear manner with respect to the central point, it is possible to obtain colors that are originally whitish-that is, before transfer or transformation-whitish only relatively little changed. In this way, the danger can be reduced that a color location, which has a distinct color, results from an originally "whitish" color location, thus making it possible that the impression of the original color information is as little as possible alienated or falsified by the conversion becomes. Advantageously, that color locus which is farther away from the central point than the other color locus is shifted further along the straight line than the other color locus. This allows for the fact that the human eye perceives differences between less saturated colors more clearly than between more saturated colors.

Advantageously, the color loci are shifted along the straight line with the aid of a non-linear mathematical function, for example an exponential function, a polynomial function or a staircase function.

Advantageously, a plurality of color loci are displaced along the straight line, whereby a color locus originally located at a boundary of the first color space is shifted to a color locus located at the corresponding boundary of the second color space. In this way, the second color space can be optimally utilized.

Advantageously, the central point is a white point. For example, it can be provided that a CIE standard color chart is used as the coordinate system and a white point as the central point, for example the point with the coordinates x = 0.3300 and y = 0.3300. If the central point is a white point, the displacement or transformation takes place along a straight line from the white point, so that the shift does not change the hue.

According to the invention, a use of a method according to the invention for programming light effects or light sequences of a light source is furthermore provided. It can be advantageously provided that the transmission of color information is performed using a display whose color space is identical to the first color space. In particular, it can be provided that the display is connected to a PC and the transmission is still performed using the PC. Alternatively it can be provided that the display is connected to the light source and the light source comprises means for carrying out the method. Further advantageously, the light source has a color space which is identical to the second color space.

The invention is explained in more detail below with reference to an embodiment and with reference to the drawings. Show it:

1 shows a sketch of an exemplary embodiment of a method according to the invention, in which a color information is converted from an sRGB color space into a light source using the CIE standard color chart. Color space is transmitted,

2 shows a sketch of the general relationship of an RGB color space to a light source color space,

Fig. 3 is an explanatory sketch for a possible implementation of

Color information from a first color space into a second, larger color space.

On the figures 2 and 3 has already been discussed above.

FIG. 1 shows a sketch of an exemplary embodiment of a method according to the invention for converting color information for controlling a light source. In this case, a color information is transmitted from a first color space into a second, larger color space using a coordinate system representing colors. Thus, an "original color information" is transferred or transformed by the conversion or transformation into a "transmitted color information", the original color information relating to colors from the first color space and the transmitted color information to colors from the second color space.

The color information may in particular be information that can be used to generate color effects or color sequences using the light source.

The light source may be a light source which has a plurality, in particular at least three, illuminants, each of which can generate light of a different color, wherein the luminous means can be dimmed independently of each other. By appropriate control can be generated with such a light source accordingly light in different colors.

The bulbs may be, for example, LEDs. Accordingly, the light source can be, for example, an LED chip with a plurality of corresponding LEDs.

It should be expressly mentioned that according to the invention, the light source can also have more than three bulbs, which generate light in each case a different color can. For example, therefore, a light source with four or five or even more such bulbs can be provided.

The coordinate system representing the colors may be, for example, the standard color chart according to CIE, 1931. However, it is also possible to use a different coordinate system for this purpose, for example the standard color chart according to CIE, 1964 or an equally spaced color chart, such as, for example, the CIE 1976 color chart.

The first color space R1 can be a color space of a color model that is used in a display. For example, it can thus be an RGB color space, for example the sRGB color space. It can be provided in particular that the display is used to program using a method according to the invention light effects or light sequences that are to be generated with the light source.

The second, larger color space R2 can be, in particular, the color space of the light source, ie the amount of all possible colors of the light that can be generated by the light source.

The second color space is, as already mentioned, larger than the first color space. Thus, in the coordinate system used, the area occupied by the first color space is smaller than the area occupied by the second color space. It is not absolutely necessary that in the coordinate system used, the boundaries of the second color space completely outside the

Borders of the first color space run. The two color spaces can therefore have intersecting boundary lines.

In order to transmit the color information, according to the invention two different color loci fl and f2, which lie in the coordinate system on a straight line g passing through a central point z, are displaced along the straight line g with respect to the central point z in a non-linear manner. In this context, "non-linear" is intended to express that the measure of the displacement is not proportional to the distance of the relevant color locus fl, f2 from the central point z, ie a non-linear extension is carried out with respect to the central point z In this case, it may be provided, in particular, that the two color loci fl, f2 lie on a half-line starting from the central point z, wherein the color loci fl, f2 are displaced exclusively along this half-line. In FIG. 1, by way of example, the two color loci fl and f2 are each marked with a cross, wherein the two color loci fl and fl lie within the first color space Rl, in the example shown within the sRGB color space. The color locus fl is shifted by the transfer or transformation of the color information into the color locus fl ', the color locus f2 into the color locus f2'. The shifted or transformed color loci fl ', G' lie within the second color space R2. In Fig. 2, the transformed color locations fl ', fl' are each marked with a small circle.

The central point z lies in a central region of the first color space Rl. For example, the central point z may be a white point, that is, for example, in the case of the CIE standard color chart shown, around the point with the coordinates x = 0.33 and y = 0.33. However, it is also possible to provide another white point as the central point, for example one of the white points designated in the literature as D50, D55, D65, D75 or D9300. By selecting a particular one of several possible white points as the central point z, special characteristics of an environment to be illuminated with the light source can be taken into account. It can therefore be provided that the central point z is selected as a function of properties, in particular light-color influencing properties of an environment of the light source.

Because the two color loci fl, f2 lie on the straight line g, which extends through the central point or emanates from it, it can be achieved that when the color loci fl, f2 are displaced or stretched into the transformed color loci fl ', fl 'No or at least no significant change in hue occurs. In this way, a color tone-preserving conversion of the color information is thus made possible overall.

In the example shown in FIG. 1, the color locus f lies farther from the central point z than the color locus f2. In this case, it is provided that the color locus fl is moved further along the straight line g than the color locus fl. In particular, it may be provided that the color locus fl, which is farther from the central point z, with respect to the original distance to the central point z and Compared to the shift of the closer color locus F2, disproportionately far shifted.

It can thus be provided that with respect to the central point z, a non-linear stretching is carried out, the imaging or stretching factor at a color location in an environment of the central point z being smaller than at a color location outside this environment. This will allow the entire color space R2, so the entire light source color space can be used. In addition, in this way it can be effected that in the vicinity of the central point z, the transformation or transformation of the color information does not lead to a color location which is originally, ie before the transmission of the color information, lying in a whitish area in the vicinity of z , is shifted so far that it receives a clearly perceptible color characteristic and in this way could contribute to a falsification of the impression of the original color information.

For example, it can be provided that the two color loci fl, f2 with the aid of a non-linear mathematical function, for example a

Exponential function, a polynomial function or a step function, along the line g are shifted.

In particular, it may be provided that a plurality of color loci are shifted along the straight line g, wherein a color location fg, which initially lies at a boundary of the first color space Rl, is shifted by the transmission to a color location fg ', which is at the corresponding boundary of the second color space R2 is. The term "corresponding" boundary of the second color space R2 denotes that boundary of the second color space R2 which, viewed from the central point z, lies in the same direction as the respective boundary of the first color space R1.

When using the exponential function, it is thus possible, for example, to provide that the color locus fg, which is originally located on the straight line g at the boundary of the first color space R1, is shifted so far at the intersection of the straight line g with the respective boundary line of the color space R1 that he is after the

Transmission as color locus fg 'is located at the corresponding boundary of the light source color space R2. For the color locus which originally coincides with the central point z, the displacement or stretching factor 1 = exp (0) (ie, the coordinate values) can be provided and for the intermediate color loci respective displacement or stretching factors resulting from a Weighting with the exponential function at the two mentioned boundary conditions.

For example, a function may also be provided in which a small neighborhood of the central point z is defined, which includes all color loci which may to some extent be called "whitish." For transmission, it may then be provided that those color loci, are originally located within this environment, are transferred 1: 1 and those color locations originally are outside the environment, are shifted so that the second color space R2 can be completely filled.

For the transmission of the entire color information, it may be provided that the method described above is carried out with arbitrary resolution accuracy for all color loci which are originally located in the first color space Rl. In this case, for example, accordingly any number of half-lines can be provided which emanate in a star shape from the central point z or from a white point.

In general, the result is that the transformation or stretching is different for each hue, because for two half-lines or for two different "hues", in general, two different distances between the boundary of the first color space and the corresponding boundary of the hue It can therefore be provided in particular that the transformation is non-linear and thereby selected for each hue so that just the boundary of the first and inner color space corresponding saturation to that of the corresponding boundary of the second and larger color space corresponding saturation is mapped.

As mentioned above, it is not absolutely necessary that the boundary lines of the first color space Rl do not overlap with the boundary lines of the second color space R2. Therefore, in the case of the aforementioned procedure, it is generally possible to form a half-line on which the color loci are pushed closer to the central point z by the transfer, so that all the color loci originally located on this half-line, after their transformation within the second color space R2 are located.

More generally, it can be provided that all color loci are located within the second color space R2 after their transformation.

Advantageously, the method according to the invention can therefore be used for programming light effects or light sequences of a light source. As already mentioned above, it can be provided that a display is used for programming the light effects or light sequences whose color space is identical to the first color space Rl. The display can be connected to a PC, whereby the transmission of the color information continues to be performed using the PC. Alternatively it can be provided that the display is connected to the light source and the light source means for performing the method having. Advantageously, the light source has a color space which is identical to the second color space R2.

Claims

claims

1. A method for converting color information for controlling a light source, wherein a color information using a color representing coordinate system (S) from a first color space (Rl) in a second, larger color space (R2) is transmitted, characterized in that for transmitting the Color information two different color loci (fl, f2) lying in the coordinate system (S) on a straight line (g) passing through a central point (z) with respect to the central point (z) are non-linearly displaced along the straight line (g) become.

A method according to claim 1, wherein the color locus (fl) farther from the central point (z) than the other color locus (£ 2) is shifted further along the line (g) than the other color locus (f2 ).

3. The method of claim 1 or 2, wherein the color loci (fl, f2) with the aid of a non-linear mathematical function, such as an exponential function, a polynomial function or a staircase function, along the line (g) are moved.

4. The method according to any one of the preceding claims, wherein a plurality of color locations along the line (g) are shifted and thereby a color locus (fg), which is originally located on a boundary of the first color space (Rl), to a color location (fg ') is moved which lies at the corresponding boundary of the second color space (R2).

5. The method according to any one of the preceding claims, wherein the central point (z) is a white point.

6. Use of a method according to one of the preceding claims for programming light effects or light sequences of a light source.

7. Use according to claim 6, wherein the transmission of the color information performed by means of a display whose color space is identical to the first color space (Rl).

8. Use according to claim 7, wherein the display is connected to a PC and the transmission is further performed by means of the PC or the display is connected to the light source and the light source comprises means for performing the method.

9. Use according to any one of claims 6 to 8, wherein the light source has a color space with the second color space

(R2) is identical.