GB1574249A - Additive colour-synthesis apparatus - Google Patents

Description

(54) ADDITIVE COLOUR-SYNTHESIS APPARATUS (71) I, JEAN MICHEL WEISS of French Nationality of 50 rue Sebastien Mercier, 75015 Paris, France, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to an apparatus for the additive synthesis of colours, the apparatus including at least one light source and providing constant-intensity illumination, a plurality of different colour filters, shutter means comprising at least one electrooptical element having a light-transmission coefficient variable as a function of an electric field applied to it so as to vary the intensity of the elementary beam of coloured light produced by each filter, a control circuit for the shutter means and means for superimposing the elementary beams of coloured light provided by the filters.

A known arrangement of this kind is described in French patent specification No.

2,211,132. This known arrangement is particularly intended to be used for making colour corrections in the copying of cinematographic films, the control circuit providing electric signals containing information as to the required intensity of the different colour components The object of the present invention is to provide an apparatus which allows a very extended range of different colours to be obtained and which is useful in many different applications in various fields, for exam ple, to provide an apparatus which may be used as a reference colour source in the field of colour printing on paper, fabric or photosensitive materials, or as a variable colour source for multi-colour image selection. In such applications it is essential to be able to encode, identify and easily and accurately reproduce all the hues which can be produced.

According to the present invention there is provided additive colour-synthesis apparatus, comprising at least one light source arranged to provide light of constant intensity, an array of different colour filters illuminated by said light source, shutter means comprising at least one electro-optical element having a light transmission variable in accordance with the magnitude of an applied electric potential so as to vary the intensity of the beam of light of an elementary colour as herein defined produced by each filter, wherein an intensity control circuit associated with each said beam includes selector means provided with numerical indications and arranged to apply to the or each respective electro-optical element an electric potential difference chosen by the selector means from one of a plurality of predetermined values determined so as to associate an individual numerical value with each intensity level of a light beam, whereby there is associated with each synthesized colour a numerical code of which the elements are representative of the respective intensities of the beams composing the synthesized colour.

Thus there is associated with each hue produced a numerical code which not only identifies the hue but, in addition, can be used to produce the hue to the extent that the elements of the code are representative of the intensity levels of the elementary colours composing the hue.

Other features and advantages of apparatus in accordance with the invention will appear from the following description given with reference to the accompanying drawings, comprising Figures 1, 2, 3 and 4 each of which schematically represents one embodiment of colour synthesizing apparatus embodying the invention.

In Figure 1, L1, L2 and L3 denote three similar light sources, for example wide spectrum lamps fed with equal constant voltage.

In the path of the light produced by the sources L1, L2, L3 are placed respective colour filters FV, FR and FB to produce, for example, green, red and blue beams, respectively. It should be noted that the number of elementary colours could be chosen greater than three, by increasing the number of filters and associated light sources. In addition, white light could equally be produced by means of an associated unfiltered source, the term 'elementary colour' is to be understood as comprehend i.lg all the primary colours and their combinations.

The beams of each colour are superimposed by means of a mixer M constituted for example by an assembly of prisms and/or mirrors and chosing a suitable arrangement of the directions of incidence of the beams and of the prisms.

In the path of the light beams produced ov each source L1, L2 and L3 and in front of or iehind each filter there is arranged an ;o-optical element 01, 02, 03 respec lively, allowing the intensity of the beam of ach colour to be varied.

Each electro-optical element 01, 02, 03 is an element in the form of a flat plate, like a Kerr cell, and is provided with an electrode on each of its faces. These elements may for example be liquid-crystal cells or, Dreferably. ferroelectric electro-optical ceramic elements provided with a transparent electrode on each face. Such ceramic element are described for example in French patent specification No. 2,156,263 rd i an article by G.M. Haertling and (?.E. Lund entitled "Hot-Pressed Ferroelectric Ceramics for Electro-Optic Applications" published in "Bulletin of the Amer ican Ceramic Society", Vol. 49, page 411.

April. 1470.

The electrodes of each electro-o-cal element 01, 02, 03 are connected o a vesoectie intensity control circuit C1, C2, C3. Each corltrol circuit includes voltage divider means to establish a controllable potential difference between the electrodes of the respective electro-optical element and thus to vary quasi-instantaneously the amount of light transmitted through this electro-optical element in the direction nor mol to to its faces.

;5ne control circuits C1, C2, and C3 are d;Fcretely variable voltage dividers. In parti i tl;. progranimable voltage dividers may be o ntrolled manually by means of push buttons or in response to numerical information suppiied on an information carrier.

The control circuits are grouped in a desk P comprising keyboards P1, P2, P3 each associated with a respective control circuit and thus with a respective elementary colour.

By applying to each key of a keyboard a numerical character, for example a digit corresponding to a predetermined intensity level of the colour associated with the keyboard, each hue produced by the synthesizer apparatus may thus be encoded by a number formed by the digits corresponding to the respective intensity levels of the elementary colours composing this hue.

Each encoded hue is thus easily and exactly reproduced later.

The simple expression of a hue by the number defining it give a concrete idea of this hue by the ratio of the primary colours that compose it, the colours always being placed in the same order in the code. This digital code thus indicates the amount of purity, of saturation, or darkening or of lightening of the hue.

It will be seen that the use of electrooptical elements such as the ceramics mentioned above allows the intensity of illumination of each colour to be varied between zero value and the maximum value available from the associated light source.

Figure 2 illustrates a second embodiment of an apparatus according to the invention.

Elements common to the apparatuses shown in Figures 1 and 2 are denoted by the same reference numerals.

The electro-optical elements 01, 02, 03 are arranged opposite three faces of a cube formed by an assembly of four prisms R1, R2, R3 and R4. Two dichroic filters F1 and F2 are arranged in the two diagonal planes of the cube.

Each of the electro-optical elements 01, 02, 03 is associated with a respective light source L1, L2, L3 and with its intensity control circuit C1, C2, C3. As before, these control circuits are grouped in a desk P comprising three keyboards P1, P2, P3.

The beam produced by the source Ll is reflected by the filter F1 and passes through the filter F2 to yield a beam of a first colour.

The beam produced by the source L2 passes through the filters F1 and F2 to yield a beam of a second colour. Finally, the beam produced by the source L3 is reflected by the filter F2 and pr s through the filter F1 to yield a beam a third colour.

All three beams have a common direction of emergence D, normal to the fourth face of the cube formed by the prisms R1 to R4, in front of which face no electro-optica element is placed.

Figure 3 illustrates a third embodiment of apparatus in accordance with the invention.

A single light source L, for example a wide-spectrum lamp, is placed behind a filter array F contituted by a mosiac of filter elements and transparent elements.

A set of filter elements FVl,FV2... FVn forms the filter providing the colour green, a set of filters FR1, FR2 ... FRn forms the filter supplying the colour red, a set of filter elements FB1, FB2 ... FBn forms the filter supplying the colour blue, and a set of transparent elements FW1, FW2 ... FWn supplies white light.

Preferably the filter elements and transparent elements associated with the different colours each occupy the same fraction of the area of the mosaic and the filter elements or transparent elements of each set are distributed over the mosaic so as to have, beyond the mosaic, beams of each colour substantially mixed together; the mixture of these beams being then achieved by means of an optical mixer M'.

In front of or behind each filter element or transparent element there is disposed an electro-optical element (not shown) such as described above each provided with a first and a second electrode. The first electrodes of the electro-optical elements associated with the same colour are electrically connected together, as are the second electrodes, these first and second electrodes being connected to a respective intensity control circuit C'1, C'2, C'3 or C'4 similar to those previously described and grouped in desk P'.

Figure 4 illustrates a fourth embodiment of apparatus according to the invention.

Three filters, respectively a green filter FV, a red filter FR and a blue filter FB, as well as a transparent element F'W occupy the four quadrants of a rotatable disc T and pass in succession in front of a light source L'. Between the light source L' and the disc T is interposed an electro-optical element 0'.

The rotary disc T carries a reference element RT which passes in succession in front of four fixed detectors D1, D2, D3, D4. The detectors may for example be magnetic detectors and the reference element may be a metal member.

Each detector is associated with a respective colour, and, in response to the passage before it of the reference element RT. yields a control signal to a synchronizing circuit CS when the filter of the colour associated with that detector appears in front of the light source L' that is to say, when the disc T occupies a particular angular position.

The synchronizing circuit CS is also connected to four intensity control circuits C"1, C"2 C"3, C"4 similar to those previously described and grouped in a desk P".

The output of the circuit CS is connected to the electrodes with which the electrooptical element 0' is provided.

The operation of the apparatus is as follows. The electro-optical element 0' being rendered opaque by the application of a potential of appropriate polarity between its electrodes. these latter are successively connected to the outputs of the intensity control circuits C"1 to cn4 by way of synchronizing circuit CS and in response to commands developed successively by the detectors D1 to D4. Each time, a voltage pulse is applied to the electrodes of the electro-optical element 0', which thus passes more or less of the light emitted by the source L' in accordance with the amplitudes of these impulses. At the end of each impulse produced by an intensity control circuit, the electro-optical element 0' is returned to its initial opaque state.

Light emitted by the source L' can therefore pass through the electro-optical element or only when one only of the filters FV, FR, FB and the transparent element FW is situated in the path of the light beam.

Since the modulation of the optical state of the electro-optical element 0' may be effected at a high frequency, the disc T may be rotated at a high speed and excellent apparent superposition of the different coloured beams is obtained without any disturbing effect upon an operator.

It should be noted that various modifications or additions could be effected to the above described embodiments of a light synthesis apparatus in accordance with the invention without departing from the scope of protection defined by the appended

Claims (7)

claims. Thus, in the case of the arrangements illustrated by Figures 1 and 3, the different light sources could be replaced by a single lamp, respectively of rectilinear and of U-shape. Wide spectrum lamps as used in carrying out the present invention are gas-discharge lamps having an emission spectrum substantially continuous throughout the visible range. WHAT WE CLAIM IS:

1. Additive colour-synthesis apparatus, comprising at least one light source arranged to provide light of constant intensity, an array of different colour filters illuminated by said light source, shutter means comprising at least one electro-optical element having a light transmission variable in accordance with the magnitude of an applied electric potential so as to vary the intensity of the beam of light of an elementary colour as herein defined produced by each filter, wherein an intensity control, circuit associated with each said beam includes selector means provided with numerical indications and arranged to apply to the or each respective electro-optical element an electric potential difference chosen by the selector means from one of a plurality of predetermined values determined so as to associate an individual numerical value with each intensity level of a light beam, whereby there is associated with each synthesized colour a numerical code of which the elements are representative of the respective intensities of the beams composing the synthesized colour.

2. Apparatus in accordance with claim 1, wherein each said control circuit comprises switchable voltage divider means.

3. Apparatus in accordance with claim 1 or claim 2 and comprising a plurality of light sources each arranged to produce a beam of light of a respective said elementary colour.

4. Apparatus in accordance with claim 1 or claim 2 including a single light source arranged to illuminate an array of filters providing beams of light of respective elementary colours.

5. Apparatus in accordance with claim 4, wherein said array of colour filters comprises a fixed mosaic of filter elements, each colour filter being constituted by a plurality of filter elements distributed over the mosaic, and that an individual electrooptical element comprising a first and a second electrode is associated with each said filter element. the first electrodes and the second electrodes of the electro-optical elements associated with the filter elements forming one colour filter being respectively connected together and connected to a respective intensity control circuit.

6. Apparatus in accordance with any one of claims 1 2 or A. wherein a single said electro-optical element is interposed between a light source and a rotary support carrving said filters.

7. Apparatus in accordance with claim 6 and comprising detector means arranged to supply signals representative of the angular position of the rotary support to a synchronizing circuit connected also to each said intensity control circuit and arranged to supply to the electrodes of said electrooptical element a potential developed by the intensity control circuit corresponding to a respective filter element disposed in the path ol the light.

S. Apparatus in accordance with any of the preceding claims wherein the or each said light source is a wide-spectrum lamp as herein defined.

Y. Additive colour-synthesis apparatus substantiallv as herein described with reference to Figure 1. Figure 2. Figure 3 or Figure 4 oi the accompanying drawings.