GB2501237A

GB2501237A - Colour crossfade engine

Info

Publication number: GB2501237A
Application number: GB1204267.7A
Authority: GB
Inventors: James Albert Powell
Original assignee: Lumonics Ltd
Current assignee: Lumonics Ltd
Priority date: 2012-03-12
Filing date: 2012-03-12
Publication date: 2013-10-23
Also published as: GB201204267D0

Abstract

A method for generating and selecting the colour produced by a colour mixing luminaire involves implementing functionality within the luminaire that automatically generates suitable colour transitions that can be controlled remotely using industry standard control protocols such as DMX or locally using the luminaire's user interface. The colours output by the luminaire may be calibrated with reference to a colour space system, such as by using standard CIE 1931 xyY chromaticity coordinates. The method is particularly suited to lighting fixtures that utilise the wavelength mixing of a plurality of different coloured light emitting diodes (LEDs) to generate a desired colour. The invention solves an inherent problem of unwanted intermediate colour output in such colour mixing luminaires that users encounter when changing from one colour to another or selecting different colours from an in-built colour palette.

Description

Page 1

TITLE OF INVENTION: COLOUR CROSSPADE ENGINE

METHOD OF COLOUR SELECTION AND COLOUR GENERATION IN LUMINAIRES

DESCRIPTION OF THE INVENTION

The invention described herein presents a method of generation and selection of colours within a colour mixing luminaire. Although reference will be made to LEDs as the primary light source within the fixture, the method equally applies to other types of illumination source.

Through the creation of a calibrated "colour crossfade engine" within the lighting fixture the user is able to select pre-defined colours from one or more colour palettes within the fixture and make smooth transitions from one palette colour to another without generating intermediate unwanted colours. The method also allows for the user to upload their own custom colour palettes via a connected personal computer or PDA using industiy standard colour definitions and use the same "engine" to manipulate and output those colours.

Figure 1 shows a typical implementation of the invention within a luminaire. The implementation involves the use of a digital controller (1) as the host for the colour crossfade engine (2). This digital controller may be a microprocessor, microcontroller or FPGA based system and the "engine" can be created in software or implemented in logic within an EPGA.

The digital controller does not need to be specific to the implementation of the colour crossfade engine and this functionality could be added to existing processor systems in a product.

A communications interface (4) is required to connect with the lighting control system and the protocol used for this communication can be any of the industry standard protocols such as DMX or ArtNET. This interface can also be used to connect the fixture to a personal computer to upload new colour palette information.

Page 2 The lighting fixture may also posses a local user interface (10) to enable colour selection if a dedicated lighting desk or controller is not available. Non volatile memory (3) is also required to store colour palette information and colour calibration parameters for the fixture.

Signals from the colour crossfade engine are then sent to the electronic drivers (5) of the light sources within the fixture. Here, four different colours of LED light sources are shown (6)(7)(8) and (9). Thcse light sourccs need not be LEDs and the technique described is not limited to any specific number of different coloured light sources.

In order for the luminaire to reproduce colours accurately and compute transistions between different selected colours, a colour space reference system is required. This implementation uses the Standard CIE 1931 xyY chromaticity coordinates as the reference for all colours within the luminaire. Although explanation is given here using the CIE 1931 coordinates, the technique can easily be adapted to work with other colour reference systems such as CIE 1976 L*,a*,b* or Hunter 1948 L,a,b colour spaces.

Figure 2 details how colours are represented on the CTE 1931 chromaticity diagram and shows how the present invention works. Red colours appear towards the right of the diagram, greens towards the top and blues towards the bottom left. Every colour can be defined by an x andy coordinate value. Whites are centred on the point x0.3, y0.3.

The actual intensity of the colour is defined by theY value of the xyY scheme and is actually a third dimension to Figure 2.

Figure 2 illustrates the problem outlined previously and shows how by the implementation of a colour crossfade engine solves the problem of intermediate colour generation. The four colours shown on the diagram indicate a small palette that may be present in a fixture. The palette selection channel would increment from Yellow (I) to Green (2), to Blue (3) and finally Red (4). Hence to change the fixture form Yellow to Red you would move through the intermediate colours blue and green, the unwanted effect. What may be required is a direct transition from Yellow(1) to Red (4) indicated by the dotted arrow. It is this transition that can be calculated by the engine.

It is by using a coordinate system of colour representation that the engine is able to compute the path to travel to change between required colours. In order for this procedure to work, in addition to all colours within the required palette to be represented as CIE coordinates, the lighting fixture must be calibrated at manufacture so the engine knows how to produce a specific colour coordinate given the light sources present in the fixture. It is prior art using speetro-radiometrie measurements of the light sources and subsequent linear matrix algebra to produce such calibration data which can then be held in the non-volatile memory of the fixture.

A critical part of the invention is how the crossfade engine is controlled by the user to transition between the required colours; a simple palette selection channel will not suffice.

Figure 3 illustrates how the control of this feature can be implemented.

Page 3 A minimum of two colour palette selection channels (3) and (4) are required, one to select the current colour to be output by the fixture and a second to select the next required colour.

Palette (1) and (2) indicate available colours Cl to C7 in each case. Although as drawn, both palcttc selection channels show the same colours available for selection, this need not be the case and a different set of colours could be programmed into each channel. Seven different colours per palette are shown for clarity however the number of colours available per channel is not limited by the invention.

Arrow (6) indicated that in this example the user requires to change from colour C3 to colour C6. It is then the work of the colour crossfade engine to calculate the correct transition within the CIE chromaticity diagram to facilitate this change.

The colour crossfade engine is controlled by a separate channel within the luminaire, indicated by erossfade channel (5) in Figure 3. The position or level of this erossfade channel determines at what point along the transition line (6) the erossfade engine calculates to.

This feature allows the user to smoothly fade been the two required colours. With the crossfade channel at one extreme of its range, the current colour is output, and when it is driven to its opposite extreme, the next colour is output in full by the luminaire. It follows that if both palette selection channels are set to the same colour, the position of the crossfade channel has no effect on the output of the luminaire.

This invention of an implemented colour erossfade engine based on a colour coordinate system and the presentation to the user of multiple palette selection channels coupled to a crossfade control solves all the problems regarding colour selection that are currently encountered in such products.

As all the colours produced by the fixture are in the form of CIE colour coordinates, user defined colour palettes are easily downloaded to the colour engine via the fixture's serial interface and stored in the non volatile memory. This is another feature not present within current designs and allows lighting designers the option to create custom palettes to their own speciation that used to be possible with traditional filter rolls.

Although the invention is described using two colour palette selection channels, this method can easily be expanded to used an increasing number of palettes and crossfade channels depending on the complexity of the lighting fixture and desired functionality.

This invention provides the user of a colour mixing luminaire with an advanced colour selection methodology. This method does not have to be the only way of selecting colours within the luminaire. This technique can be implemented alongside other more basic traditional methods of colour selection within the same luminaire.

Claims

Page 4DESCRIPTION OF CLAIMS1. An intelligent colour mixing luminaire consisting of at least two different coloured light sources whereby each independent colour has its intensity controlled remotely via an electronic circuit.
2. An intelligent colour mixing luminaire according to claim 1, in which the light sources are light emitting diodes LEDs
3. An intelligent colour mixing luminaire according to claim 1, in which the controlling circuit is a microprocessor or equivalent device with a communication port to allow the luminaire to be remotely controlled and programmed.
4. An intelligent colour mixing luminaire according to claim 3, whereby the light sources and controlling circuitry are calibrated with reference to an internationally recognised colour coordinate system.
5. An intelligent colour mixing luminairc according to claim 4 where colour palettes based on the reference colour coordinate system can be saved within the fixture.
6. An intelligent colour mixing luminaire according to claim 5 where custom colour palettes can be uploaded by the user through the communications port from a personal computer or PDA device.
7. An intelligent colour mixing luminaire according to claim 5 further comprising a software or hardware solution that allows the luminaire to calculate colour transitions automatically between different colours present in the palette using the chosen colour coordinate system.
8. An intelligent colour mixing luminaire according to claim 7 whereby two or more colour palettes are presented to the user via control channels in order to select the present and next colour required to be output by the luminaire.
9. An intelligent colour mixing luminaire according to claim 8 further comprising a least one further control channel presented to the user to control the internally generated transition from present colour to next colour.