FR2887642A1 - Image projector`s e.g. overhead video projector, imager e.g. micro-display, illuminating method, involves utilizing LEDs of different colors to provide illumination beam with sub-beam sequences each comprising clustered antagonist colors - Google Patents

Abstract

The method involves utilizing light emitting diodes (100) of different colors, where the diodes provide a sequential illumination beam (102) for an imager (105) of an image projector. The illumination beam has sequences of monochromatic illumination sub-beams comprising four colors such as red, green, blue and yellow. Each sequence comprises pairs of clustered antagonist colors e.g. blue-yellow or yellow-blue and green-red or red-green. Independent claims are also included for the following: (1) an illumination system illuminating an imager of an image projector, comprising light emitting diodes (2) an image projector comprising an imager and an illumination system.

Description

Method of illuminating an image projector imager,

  projector and corresponding system.

1. Field of the invention

  The invention relates to the field of image projection.

  More specifically, the invention relates to an illumination system based on light emitting diodes (or LED) for imager (also called micro-display of the English micro-display) in a video projector type front or backlight.

2. State of the art

  According to the state of the art, projectors comprise at least one imager which is illuminated by an illumination beam created by LEDs. Each imager comprises an array of pixels arranged for example in rows and columns on a substrate forming an active matrix. The light from the illumination system is modulated after passing through the imager (s) in the case of transmissive imagers or after reflection on the imager (s) in the case of reflective imagers. Such a system is described, for example, in the patent document EP1397792 filed by the company Infocus. This document provides LEDs that can be red, green, blue, cyan, yellow or white. This technique has the disadvantage of generating a rainbow effect (or rainbow effect or color break-up in English). This phenomenon is related to the use of a sequential display mode of images of different colors on a screen; it is associated with a spectator's perception of the decomposition or separation of colors into its primary components when, for example, certain objects of the image move rapidly or at a sudden movement of the head, a blinking of eyes, or any other sudden spatial variation of the retinal image of the observed scene, whatever the conditions of observation. This phenomenon is also manifested for still images, for example when the viewer's eyes quickly scan the screen, when the observer's eyes are subjected to nystagmus or micro-accommodation phenomenon, or for fast moving images with a fixed observer.

3. Summary of the invention.

  The invention aims to overcome these disadvantages of the prior art.

  More particularly, the invention aims to minimize the phenomenon of color break-up while maintaining a projection of good quality images.

  For this purpose, the invention proposes a method of illuminating an image projector imager using electroluminescent diodes of different colors, the diodes being adapted to provide a sequential illumination beam of the imager, the illumination beam comprising monochrome illumination sub-beam sequences, themselves comprising at least four colors respectively red, green, blue and yellow. According to the invention, each sequence comprises at least one pair of grouped antagonistic colors.

  Preferably, the antagonistic colors are grouped in pairs, each sequence comprising at least one pair (blue, yellow) or (yellow, blue) and at least one pair (green, red) or (red, green).

  According to a particular characteristic, each sequence comprises at least one pair (yellow, blue), the yellow color being placed before the blue color in each sequence.

  According to another particular characteristic, each sequence comprises at least one pair (green, red), the green color being placed before the red color in each sequence.

  According to advantageous characteristics, each sequence comprises at least one fifth cyan or magenta color and, preferably, at least one sixth cyan or magenta color, different from the fifth color.

  The invention also relates to an illumination system for illuminating an image projector imager comprising light-emitting diodes of different colors, adapted to provide a sequential illumination beam of the imager, the illumination beam comprising sequences monochrome illumination sub-beams, themselves comprising at least four colors respectively red, green, blue and yellow. According to the invention, the system comprises light emitting diode control means such that each sequence comprises at least one pair of grouped antagonistic colors.

  Preferably, the light-emitting diode control means controls the diodes so that the antagonistic colors are grouped in pairs, each sequence comprising at least one pair (blue, yellow) or (yellow, blue) and at least one pair (green, red). ) or (red, green).

  In addition, the invention relates to an image projector, comprising: - at least one projection lens; at least one imager; at least one illumination system, according to the invention, as described above.

4. List of figures.

  The invention will be better understood, and other features and advantages will appear on reading the description which follows, the description referring to the accompanying drawings in which: - Figure 1 is a very schematic block diagram of a backlight according to one embodiment of the invention; Figure 2 shows an illumination system implemented in the backlight of Figure 1; and FIG. 3 illustrates a timing diagram of the control signals of the illumination system of FIG. 2.

  5. Detailed description of the invention.

  The general principle of the invention is therefore based on the use of LEDs adapted to produce beams whose color varies according to sequences which comprise at least blue, red, green, cyan and yellow. More precisely, according to the invention, in each sequence, antagonistic colors are grouped in pairs, with blue and red being respectively associated with yellow and green; in other words, the sequence comprises at least one pair (blue, yellow) or (yellow, blue) and at least one pair (green, red) or (red, green). Preferably, each sequence also comprises the magenta and / or cyan color.

  As seen above, the object of the invention is to reduce the phenomena of "color break up". For this, the invention will exploit the intrinsic characteristics of human vision related to the use of antagonistic color channels.

  It is recalled that the theory of trichromaticity was born in 1802 with the work of Thomas Young, then developed in 1866 by Helmholtz.

  It is based on the mixture of three colored channels leading to the constitution and discrimination of all perceptible colors. This principle is used today by the majority of visualization and display devices that work by illuminating an image since they reconstitute the images from the 3 R, G, B channels. The antagonistic channel theory was proposed by Hering in 1872. It highlights the existence of a response of the visual system 5 according to 3 antagonistic channels - The red-green channel; The blue-yellow channel; -And the black-white achromatic channel called luminance.

  This very schematic description represents the practical effects of physiological processes and oversimplifies things.

  This property is nevertheless illustrated by the fact that it is possible to perceive either a red or a green, but never a greenish red, or a reddish green. It is the same for blue and yellow. Such an observation leads to the fact that the stimulation of a retinal surface with a yellow color, for example, inhibits the perception of blue on the same surface during the stimulation phase, and vice versa. It is the same for the so-called antagonistic colors that are red and green. In addition, a physiological consideration of the visual system shows that the stimulation of a retinal area by a color such as yellow will make this same area much more sensitive to the opposite color of said antagonist channel used immediately after stopping said stimulation; either blue, and vice versa. This is also demonstrated for the red-green chromatic channel, and is explained by the inertia of the polarization and depolarization chemical mechanisms of the cortical transmission system of visual information. This antagonism is also highlighted by the phenomenon of simultaneous contrast or "after images" in the English language that wants to set a certain time for a green pattern, we will see the same pattern in red if we fix immediately after a surface with a white background. Thus, by simplifying the process, it can be considered that for the human eye, green increases sensitivity to red, and conversely, that yellow increases sensitivity to blue, and vice versa. Different experiments by different researchers have given rise to publications, and highlight the existence of antagonistic color channels at the level of the visual perception of the human eye.

  All the work on the vision of colors, and more precisely on the antagonistic aspect of the channels composing it, led to the standardized simplified model comprising: - a receptor level with 3 types of photoreceptors for photopic vision, responsible for perception colors: the cones L, M, S, each being individually sensitive to a range of different wavelengths (red, green, blue).

  - a post-receptoral level (horizontal cells then visual cortex) where the opposition mechanism of the colors takes place.

  FIG. 1 is a very schematic diagram of a retro-projector 1 according to a first embodiment of the invention.

  The projector 1 comprises: an illumination system 10; an objective 11 receiving an illumination beam 16 created by the illumination system 10 and producing a beam 15; a rear projection screen 14 illuminated by the beam 15; and two folding mirrors 12 and 13 folding the beam 15 and reducing the depth of the projector 1.

  The lens 11, the mirrors 12 and 13 and the screen 14, as well as their arrangement are well known to those skilled in the art and are not detailed further.

  FIG. 2 illustrates in detail the illumination system 10 with transmissive imager and which comprises: a network of illumination LEDs 100; a lens 101 collimating the beams transmitted by each of the LEDs of the array 100 to produce a substantially collimated beam 102 (a beam being here substantially collimated if it does not diverge more or less 6 with respect to its optical axis); a convergence lens 103; a transmissive type imager 105 (transmissive LCD) substantially perpendicular to the axis of the beam 102, illuminated by the beam 102 having passed through the lens 103, the imager 105 producing an imaging beam 17; an LED driver 113 which manages the switching on and off of each of the LEDs of the network 100 via a link 115; an imager driver 114 which controls the imager 105 via a link 116 from the data associated with the images to be projected, which it receives sequentially via a link 20; and a controller 110 which controls the drivers 114 and 114 respectively via the links 111 and 112 by transmitting a synchronization signal and / or a signal representative of the color of the beam which illuminates the imager.

  The array of LEDs comprises red, green or blue LEDs, which respectively produce sub-beams of the beam 202 respectively red, green and blue when they are lit. The distribution of the LEDs on the network 200 is such that the illumination of the imager by each of the red, green and blue sub-beams is substantially uniform. The number of LEDs of each color depends on the respective performance of these LEDs and is such that the sub-beams have a similar intensity. These LEDs are, for example, monochrome power LEDs manufactured by Osram or LumiLeds.

  As an illustration, the array of LEDs comprises two matrices juxtaposed to form a network with four rows and four columns: a 2x4 array of eight green LEDs each having a luminous efficiency of 170mW / mm2 (totaling 1360mW / mm2) and a matrix 2x4 with four blue LEDs and four red LEDs each having a luminous efficiency of respectively 350mW / mm2 (blue LEDs, totaling 1400mW / mm2) and 280mW / mm2 (red LEDs, totaling 1120mW / mm2). According to one variant, the network comprises four columns each with two green LEDs, one red LED (or R) and one blue LED (or B), the green LEDs (or V), on the one hand, and the red and blue LEDs. being grouped in pairs and the pairs of LEDs of different colors being staggered in the array so as to produce a substantially uniform beam (in a synthetic manner the four columns are for example: GGRB, RBGG, GGRB and RBGG.

  When LEDs of different colors are lit simultaneously, the illumination beam corresponding to the superposition of the monochrome sub-beams, is yellow (when the red and green LEDs are lit), cyan (when the blue and green LEDs are lit), magenta ( when the red and blue LEDs are lit) or white ((when the red, blue and green LEDs are lit).

  According to a variant of the invention, the imager driver 114 transmits directly to the LED driver 113, a synchronization signal and / or a signal representative of the color of the beam that illuminates the imager, the controller 110 then being unnecessary.

  FIG. 3 shows a timing diagram of the control signals 115 (the signal being assimilated to the connection ensuring its transport) of the LED array 100 as a function of the color of the generated beam 102 (or of the signal 111) during the transmission of two images corresponding to time intervals respectively 36 and 37.

  According to the invention, the colors of the illumination beam 102, having an antagonistic character are grouped in pairs. Thus, for each image, the imager 105 is illuminated by the illumination beam 102 in a sequence of monochromatic sub-beams successively magenta (or M), cyan (or C), yellow (or Y of the English Yellow) , blue (or B), green (or G of English Green) and red (or R), this sequence being noted MCYBGR (the ordered succession of letters corresponding to each color of the sequence). Thus, in the sequence, there are two pairs 34 YB (yellow, blue) and 35 GR (green, red) of colors having an antagonistic character. The presence in the sequence of these two pairs of antagonistic colors makes it possible to reduce the breakup color phenomenon.

  Controls 115 of the red, green and blue LEDs 31 to 33, respectively, are indicated in a low state (or 0) when turned off and in a high state (or 1) when turned on.

  Each time interval corresponding to an image is divided into six sub-intervals of time during which the LED commands are fixed. Thus, in a first subinterval, the red and blue LEDs are lit forming a magenta monochrome illumination beam 102. Then, the red LEDs go off and the green LED turns on, the resulting monochrome beam 102 being cyan. Then, the monochrome beam successively takes the yellow and blue colors corresponding to the antagonistic pair of colors 34, the red and green LEDs then only the blue LEDs being lit. Then, the beam successively takes the green and red colors corresponding to the antagonistic pair of colors 35, the green LEDs then the blue LEDs being successively lit during the two following subintervals.

  In each sequence, the yellow color is placed preferentially before the blue color and / or the green color is placed before the red color. Indeed, blue (respectively red) transmits less power than yellow (respectively green); if the observer is sensitized to blue (respectively red), yellow (respectively green) will appear more powerful and vice versa. Also, it is better to have a yellow-blue pair rather than blue yellow and green-red rather than red-green.

  In addition, to limit the color break-up effect, it is preferable to have colors that emit a lot of power (ie yellow, green and cyan) at the time center of each sequence while keeping the pairs grouped together. by antagonistic colors. Thus, a good sequence is for example the sequence Magenta-Blue-Yellow-Cyan-Green and Red.

  According to a variant of the invention, the LED array 100 also comprises Cyan and / or Yellow LEDs. In this case, to obtain a yellow illumination beam 102 (respectively cyan), the yellow LEDs (respectively cyan) are lit and the red LEDs (respectively blue) and green LEDs are totally or partially extinguished.

  Of course, the invention is not limited to the embodiments described above.

  In particular, the invention is compatible with any type of headlamps (in particular headlamps or backlights) comprising at least one imager illuminated by a sequentially colored beam from colored LEDs.

  The person skilled in the art can also adapt the invention to any type of mechanical and / or optical structure using the colored LEDs. It can in particular vary the number of LEDs of each color (for example an LED of each color (high power LED) to more than ten LEDs of each color). The position of the LEDs in the illumination system may vary: they may be in a flat monolithic network as illustrated with reference to FIG. 3 or may be associated with several monochrome LED arrays (for example, three LED arrays respectively green, blue and red and possibly yellow and / or cyan) on the same plane or not (the structure may include dichroic return mirrors, allowing the combination of beams of different colors in a single beam illuminating the imagers) or remote from the imager, the colored beams being transmitted to the imager (s) via appropriate optical systems (for example via optical fibers).

  The invention is also not limited to the case where the illumination times corresponding to each color in a sequence associated with an image are identical but also relates to the case where they are different.

  The invention is also compatible with any type of imager; Thus, it applies not only to projectors with transmissive LCD (Liquid Crystal Display), but also to projectors with DMD (Digital Micromirrors Device) micromirrors. the company Texas Instruments) or LCOS (Liquid Crystal On Silicon) (the person skilled in the art integrating the appropriate optical elements (polarizers, lenses, mirrors, ....) between the source of illumination and the imager.

  More generally, the invention relates to a projection device with an illumination beam comprising color sequences with n different colors (n being, for example, 4, 5 or 6) or a display system implementing such a device, each sequence comprising antagonistic colors grouped in pairs, that is to say following each other in the time sequence. Thus, each sequence has at least one pair of GR or RG (green, red) antagonistic colors and optionally at least one pair of BY and YB antagonist colors (blue, yellow).

  Thus, the sequences comprising four colors corresponding to three primary colors and a complementary color, at least two antagonistic colors being grouped in pairs are compatible with the invention. As an illustration and not exhaustive, as indicated above, the temporal sequences (in the LED-based illumination beam) comprising the following colors are compatible with the invention: YBGR (or yellow-blue-green-red); BYRG (or blue yellow red green); YBRG (or yellow blue red green); - BYGR (or blue yellow green red); BMGR (or red green magenta blue); - BGRM (or magenta red green blue); BMRG (or magenta red green blue).

  The BYGR sequence is particularly advantageous, the human visual system being more sensitive to yellow and green colors which are thus placed in the center of the sequence.

  Likewise, the sequences comprising five colors corresponding to three primary colors and two complementary colors, at least two antagonistic colors being grouped in pairs are compatible with the invention. By way of non-exhaustive illustration, as indicated above, the temporal sequences (in the LED-based illumination beam) comprising the following colors in the order indicated are compatible with the invention: YBCGR (or yellow-blue) cyan - red green); YBCRG (or yellow - blue - cyan - red green); BYCGR (or yellow blue - cyan - red green); YBGRC (or yellow - blue - green cyan red); - CYBGR (or cyan - yellow - blue - red green); YBGRM (or yellow - blue green - magenta red).

  The BYCGR sequence is particularly advantageous, the human visual system being more sensitive to yellow and green colors which are thus placed in the center of the sequence.

  Likewise, the sequences comprising six colors corresponding to three primary colors (red, green, blue) and three complementary colors (cyan, magenta, yellow), at least two antagonistic colors being grouped in pairs are compatible with the invention. By way of non-exhaustive illustration, as indicated above, the temporal sequences (in the LED-based illumination beam) comprising the following colors in the order indicated are compatible with the invention: GRCMYB (or green-red-cyan - magenta - blue yellow); GRMCYB (or Red Magenta Green Cyan Yellow Blue); - GRYBMC (or green red yellow blue magenta cyan); - MYBCGR (or yellow magenta blue - red green cyan). The examples given above are not, of course, exhaustive and many other sub-beam sequence combinations created by LEDs (color and color order) are possible. Preferably, in order to further reduce the break-up color phenomenon, according to the invention, each sequence comprises two pairs of antagonistic colors grouped together (green, red) and (yellow, blue), as, for example, in the following combinations : -YBGR (or yellow blue - red green); YBCGR (or yellow - blue - cyan - red green); YBGRM (or yellow - blue - green - magenta red); -GRCMYB (or red green - cyan - magenta - blue yellow); GRYBCM (or green - red - yellow blue - cyan magenta); - MCYBGR (or magenta cyan - yellow blue green red).

  According to other variants, the sequences of the illumination beam comprise a white subsequence obtained by the simultaneous lighting of blue, green and red LEDs (and possibly cyan and / or magenta LEDs) and / or white LEDs, the pairs of antagonistic colors remaining grouped according to the invention. The sequences thus obtained thus comprise five, six, seven or more colors.

Claims (1)

12 CLAIMS   A method of illuminating an image projector imager (105) employing light-emitting diodes (100) of different colors, said diodes being adapted to provide a sequential illumination beam (102) thereof imager, said illumination beam comprising monochrome illumination sub-beam sequences, themselves comprising at least four colors respectively red, green, blue and yellow, characterized in that each sequence comprises at least one pair (34, 35) of grouped antagonistic colors.   2. Method according to claim 1, characterized in that the antagonistic colors are grouped in pairs, each sequence comprising at least one pair (34) (blue, yellow) or (yellow, blue) and at least one pair (35) ( green, red) or (red, green).   3. Method according to any one of claims 1 and 2, characterized in that each sequence comprises at least one pair (yellow, blue), the yellow color being placed before the blue color in each sequence.   4. Method according to any one of claims 1 to 3, characterized in that each sequence comprises at least one pair (green, red), the green color being placed before the red color in each sequence.   5. Method according to any one of claims 1 to 4, characterized in that each sequence comprises at least a fifth cyan or magenta color.   6. Method according to claim 5, characterized in that each sequence comprises at least one sixth cyan or magenta color, different from the fifth color.   An illumination system (10) for illuminating an image projector imager (105) comprising light-emitting diodes (100) of different colors, adapted to provide a sequential illumination beam (102) of said imager , said illumination beam comprising monochrome illumination sub-beam sequences, themselves comprising at least four colors respectively red, green, blue and yellow, characterized in that it comprises means (110, 113) of controlling light emitting diodes so that each sequence comprises at least one pair (34, 35) of grouped antagonistic colors.   8. System according to claim 7, characterized in that said light-emitting diode control means controls said diodes so that the antagonistic colors are grouped in pairs, each sequence comprising at least one pair (blue, yellow) or (yellow, blue ) and at least one pair (green, red) or (red, green).   9. Image projector (1), characterized in that it comprises: at least one projection lens (11); at least one imager (105); at least one illumination system (1) according to any of claims 7 to 8 for illuminating said imager.