EP0539261A1 - Method and apparatus to optimise the performance of a liquid crystal matrix display as a function of the viewing angle - Google Patents

Abstract

The device of the invention includes an image suite consisting of an image generator (6), of a microregion processing unit (12), of a screen interface (31) and of an LCD screen (3). In order to optimise the performance of the screen as a function of the viewing angle, the position of the observer (sensor 33) is detected and, as a function of this position, the appropriate luminosity profile of the microregions of the screen is selected (32). <IMAGE>

Description

The present invention relates to a method and a device for optimizing the performance of a liquid crystal matrix screen as a function of the viewing angle.

A problem often encountered by users of liquid crystal screens (LCD), in particular using nematic liquid crystals in a helix, is the deterioration of the legibility of the images presented when one deviates from an axis of observation. normal on screen.

This degradation is characterized by a decrease in contrast and a colorimetric drift (desaturation or inversion of colors).

This phenomenon is mainly related to the fact that an LCD screen has a limited field of observation.

This field of observation is further reduced when presenting images containing shades of gray, for example synthetic imagery, requiring treatment of anti-aliasing type, to improve image quality.

According to the state of the art, this deterioration in performance is compensated for by an overall adjustment of the addressing voltages of the liquid crystal screen, by means of a control potentiometer placed close to the screen.

The subject of the present invention is a method for automatically obtaining optimum readability of the images presented on a liquid crystal screen, whatever the position of the observer relative to the screen, therefore whatever the direction of observation, as well as a device for implementing this process.

The method according to the invention, for optimizing the performance of a liquid crystal matrix screen as a function of the angle of observation, consists in dividing the space of observation, represented by a half-sphere, in front of the screen, in elementary zones corresponding to the various locations where the observer may be to look at the image, to associate a particular processing of the image to be presented on the screen at each zone, by determining for each zone a set of micro-ranges, themselves composed of several pixels of the screen, the luminance level of each pixel is determined experimentally, and the chrominance level of each micro-range, by function of the observation angle, to obtain optimal readability, to memorize these values, then, in normal use, to detect the position of the observer relative to the screen, and to modify one at least one parameters for processing the image to be displayed on the screen as a function of the stored values and corresponding to the angle of observation detected.

The device according to the invention comprises a device for detecting the position of the observer relative to the screen, connected by a processing device to a device for weighting the characteristics of brightness and / or colorimetry of the images to be presented. on a liquid crystal screen, the processing device determining, from the information provided by the detection device, the skills necessary for weighting.

• la figure 1 est un bloc-diagramme simplifié d'un dispositif d'optimisation conforme à l'invention ;
• la figure 2 est un bloc-diagramme d'un circuit de traitement du dispositif de l'invention ;
• les figures 3 et 4 sont respectivement des blocs-diagrammes de la mémoire d'écran et du circuit de corrélation du circuit de la figure 2 ;
• la figure 5 est un diagramme expliquant l'adressage de la mémoire d'écran du dispositif de l'invention, pour différentes positions d'une microplage ;
• la figure 6 est un diagramme des différentes étapes du traitement de microplages selon l'invention ;
• la figure 7 est un bloc-diagramme de la chaîne de traitement d'images du dispositif de l'invention ;
• la figure 8 est un schéma simplifié d'une unité de traitement dédiée pouvant faire partie de la chaîne de traitement de la figure 7 ;
• les figures 9 à 11 sont des diagrammes illustrant la détection de direction d'observation selon le procédé de l'invention, et
• la figure 12 est un graphique montrant quatre exemples de valeurs d'amplitudes de plages d'un jeu de microplages en fonction de différents angles d'observation.

The present invention will be better understood on reading the detailed description of an embodiment, taken by way of nonlimiting example, and illustrated by the appended drawing, in which:

• Figure 1 is a simplified block diagram of an optimization device according to the invention;
• Figure 2 is a block diagram of a processing circuit of the device of the invention;
• FIGS. 3 and 4 are respectively block diagrams of the screen memory and of the correlation circuit of the circuit of FIG. 2;
• FIG. 5 is a diagram explaining the addressing of the screen memory of the device of the invention, for different positions of a microplate;
• FIG. 6 is a diagram of the different stages of the treatment of microplates according to the invention;
• FIG. 7 is a block diagram of the image processing chain of the device of the invention;
• Figure 8 is a simplified diagram of a dedicated processing unit that can be part of the processing chain of Figure 7;
• FIGS. 9 to 11 are diagrams illustrating the detection of direction of observation according to the method of the invention, and
• FIG. 12 is a graph showing four examples of range amplitude values of a set of microplates as a function of different observation angles.

FIG. 1 shows the block diagram of the device of the invention. This device essentially comprises: a device 1 for detecting the position of the head of the observer 2, a liquid crystal screen (LCD) forming part of a display device 4, which is connected to the detection device 1 by a processing device 5. The display device 3 is also connected to an image generator 6 (synthetic and / or video images).

• Dispositif de détection de type électromagnétique :

   Un dispositif électromagnétique de détection de position est généralement composé de trois éléments :

• une source de référence, encore appelée radiateur, dont le rôle est d'émettre un champ magnétique de référence positionnant ainsi l'origine et l'orientation du repère tridimensionnel lié à l'espace d'évolution.

We will describe below various known devices for detecting the position of the head of an observer, which can be used as device 1.

• Electromagnetic type detection device:

An electromagnetic position detection device generally consists of three elements:

• a reference source, also called a radiator, whose role is to emit a magnetic reference field thus positioning the origin and the orientation of the three-dimensional reference linked to the space of evolution.

• un capteur de position dont le rôle est de recevoir suivant trois directions de l'espace, le rayonnement de référence émis par la source.

Le niveau énergétique reçu suivant les trois directions est caractéristique des position et orientation du capteur par rapport à la source de référence.
Ce capteur est généralement porté par l'observateur ;

• une unité de contrôle dont le rôle est de piloter la source et le capteur électromagnétique, de traiter les signaux issus du capteur pour en extraire les informations de positions (trois distances) et d'orientation (trois angles) de celui- ci par rapport à la source, de transmettre ces informations de manière cyclique et automatique sur une liaison informatique de type série à la cadence de 30 Hz par exemple.

This source is generally placed near the display screen;

• a position sensor whose role is to receive in three directions of space, the reference radiation emitted by the source.

The energy level received in the three directions is characteristic of the position and orientation of the sensor relative to the reference source.
This sensor is generally worn by the observer;

• a control unit whose role is to control the source and the electromagnetic sensor, to process the signals coming from the sensor to extract the information of positions (three distances) and orientation (three angles) from it relative to the source, to transmit this information cyclically and automatically over a serial type computer link at a rate of 30 Hz for example.

• précision de positionnement > 7 mm (valeur moyenne) ;
• précision d'orientation > 1.5° (valeur moyenne).
• Dispositif de détection de type électro-optique :

The average performances of such devices, for a source-sensor distance <700 mm are:

• positioning accuracy> 7 mm (average value);
• orientation accuracy> 1.5 ° (average value).
• Electro-optical type detection device:

• une source d'émission optique, comme par exemple une diode électro-luminescente émettant un rayonnement infrarouge sous un angle solide de 180°.

Cette source est généralement portée par l'observateur ;

• deux photo-capteurs de surface sensible 10 mm x 10 mm environ, associés à une optique permettant d'imager la source sur la surface active des capteurs.

Chaque détecteur permet de connaître la position de la source dans un plan de l'espace.
L'intersection de deux plans de l'espace judicieusement choisis permet de déterminer la troisième dimension.
Ces photo-capteurs sont généralement situés à proximité de l'écran de visualisation ;

• une unité de contrôle dont le rôle est de calculer, à partir des informations fournies par les capteurs, la position de la source dans l'espace d'observation, d'émettre cette position (trois distances) de manière cyclique et automatique sur une liaison informatique de type série, à la cadence de 30 Hz par exemple. La précision de tels dispositifs est de l'ordre de 1 mm pour une distance d'observation de 1 m.

An electro-optical position detection device generally consists of:

• an optical emission source, such as for example a light-emitting diode emitting infrared radiation at a solid angle of 180 °.

This source is generally carried by the observer;

• two photo-sensors of sensitive surface approximately 10 mm x 10 mm, associated with an optic making it possible to image the source on the active surface of the sensors.

Each detector makes it possible to know the position of the source in a plane of space.
The intersection of two carefully chosen planes of space makes it possible to determine the third dimension.
These photo-sensors are generally located near the display screen;

• a control unit whose role is to calculate, from information provided by the sensors, the position of the source in the observation space, to transmit this position (three distances) cyclically and automatically on a link serial type computer, at a rate of 30 Hz for example. The precision of such devices is of the order of 1 mm for an observation distance of 1 m.

Any other position detection device can be used in the invention, even if its performance is lower than that of the two previous devices. It is also possible to use devices for detecting the direction of gaze of the observer.

For example, a device having an accuracy better than 20 mm for an observation distance of 1 m ensures the positioning of the borders of the different zones at better than 1.2 °.

The display device 3 is of the type described in French patent 2,619,982 of the Applicant. This known device is advantageously modified in the following manner in order to be able to operate in real time with high definition, by using the screen memory to carry out the correlation of the micro-ranges, this screen memory being organized in an identical manner to that of the pixels of the micro-ranges, and associated with a matrixed addressing bus.

FIG. 2 shows the block diagram of an embodiment of the screen control device 3, forming part of the display device 4 (namely a circuit forming part of the unit 12 described below with reference in Figure 7).

This control device is connected to the image generator 6. This generator 6 is connected, by a line 7A, to a management circuit 7, and by a bus 8A to a micro-range generator 8. The generator 6 is also connected , by one addressing command line 6A, to the management circuit 7 and to an address generator 9. This generator 9 addresses a screen memory 10, and is connected, by a bus 10A, to a circuit 11 for permutation and correlation. The bus 10A has a link 11A to the memory 10 and link 11B to the circuit 11.

The functional unit comprising the elements 7 to 11 will be called here microplage processing unit, and referenced 12 as a whole.

The management block 7 performs various functions. It controls, via line 13, the address generator 9 according to the mode of access to the unit 12, write access in image processing, read access in image display. Block 7 provides the generator 8, on line 14, with the microplate selection parameters, established as mentioned in FR-A-2 619 982, the selection being made from the image data supplied by the generator 6 on bus 8A. Block 7 controls, via line 15, the permutation means, described below, of block 11.

For a quad structure display, the microplate selection parameters are provided on six bits, including two bits for coding the quad structure and four bits for coding the observation conditions. For a trio structure display, these parameters are provided four coding bits for the trio structure and two coding bits for the observation conditions.

Block 7 also controls the screen memory 10 via the address generation block 9 and line 16, and the address by an address bus 17.

The screen memory 10 (FIG. 3) consists of a matrix of elementary memories, or memory boxes, 18¹ to 18¹⁶, organized in an identical manner to that of the pixels of the processing microplates, with in this case sixteen RAM memories of capacity of 64 K words of 4 bits each. The bus 17 for addressing the memory 10 is divided into a column address bus 19C and a line address bus 19L and which allows to simultaneously address all the boxes, (for example in 30 ns), to write or read a matrix of pixels of the same structure as the processing microplates. When, for example, the writing of a microplate in the screen memory 10, the pixels of the microplage are thus written respectively in all the elementary memories of the screen memory. All the elementary memories of the same column receive by the bus 19C the same address and all the elementary memories of the same line receive by the bus 19L the same address.

It will be noted that the information for reading the screen memory 10, for display on the screen, comes from a line 20, sequentially, via (since it is a matrix memory) d a multiplexer 21 controlled by the line 16. The presentation of the pixels on a line of the display screen, for example, is effected by simultaneous sending of the succession of the four pixels, with the same line address, of the four elementary memories respective lines of the screen memory. The column addresses are incremented here by 4 after each access to the screen memory. The lines of the screen memory are here read 4 by 4, that is to say that the line addresses are incremented by 4 every 4 lines.

By convention, and we can consider others, the basic row and column addresses delivered by generator 6 on row 6A correspond to the coordinates, on the display screen, of the point common to the four central pixels of the microplage associated. The addresses of the various elementary memories 18¹ to 18¹⁶ are determined from the X, Y coordinates of the pixel of the screen to be processed, delivered here by the synthetic symbol generator, or by the analog-digital converter associated with the video generator.

In image processing mode, the generator 9 provides here 4 column addresses ADRX₁-ADRX₄ and 4 row addresses ADRY₁-ADRY₄, in this case on 8 bits, the coordinates X and Y being supplied on 10 bits each, in the following manner, not exclusive of the invention:
ADRX₁ = (X + 1) / 4 for the 1st column of boxes;
ADRX₂ = X / 4 for the 2nd column of boxes;
ADRX₃ = (X-1) / 4 for the 3rd column of boxes;
ADRX₄ = (X-2) / 4 for the 4th column of boxes;
ADRY₁ = (Y + 1) / 4 for the 1st line of boxes;
ADRY₂ = Y / 4 for the 2nd line of boxes;
ADRY₃ = (Y-1) / 4 for the 3rd line of boxes;
ADRY₄ = (Y-2) / 4 for the 4th line of boxes;

In display mode on the screen, the base address X, Y is produced in the generator 9 in order, as developed above, to cause a reading of the screen memory, the addresses applied to the elementary memories being determined as in writing mode.

Block 11 (FIG. 4) ensures, in circuits 22, for example of the "PAL" type, the permutation of the data supplied, on line 8B, by the microplate generator 8, under the control, by line 15, of the management block 7 and, in circuits 23, for example of the "PAL" type, the correlation of the talents thus reorganized with the talents read in screen memory, by line 11B, before writing, by line 11A, the microplates correlated in the screen memory 10, the lines 11A and 11B being grouped together, at the screen memory 10, in the bus 10A (FIG. 3). The permutation circuits 22 ensure, before correlation, the coherence between the microplates coming from the microplate generator 8 and those which are read in screen memory 10, so that the respective pixels of the same color correspond and can be correlated.

For example, the sixteen elements of a microplage supplied by the generator 8 are identified by the first sixteen letters of the alphabet arranged as follows:

In FIG. 5 are represented four positions of microplates in the screen memory corresponding to four different addresses X, Y. In the top left is illustrated the initial position of the microplage for coordinates X, Y providing identical addresses in all boxes of the screen memory 10. In this position, there is a direct correspondence between the elements of the microplage and those of the matrix read in the screen memory 10: there is no permutation to be carried out. Above right in FIG. 5 is illustrated the block of elements read in the screen memory corresponding to an incrementation of one unit of the coordinate X, that is to say to a horizontal displacement towards the right d 'a pixel; the correspondence between the elements of the memory and those of the microplage implies a shift of the latter by one element to the left:

Thus, in the horizontal direction, four cases of permutation are possible, according to the necessary offset, from 0 to 3, taking into account the value of X. It is the same in the vertical direction, taking into account the value of Y. Globally, for any X, Y coordinates of the center of the microplage, sixteen different cases of permutation can arise, under the command, by line 15, of the management block 7. Bottom left in FIG. 5 is represented the microplage with an increment of one of the Y coordinate; bottom right is represented the microplage with an incrementation of two units of the two coordinates X and Y.

The correlation circuits 23 operate in parallel on all the elements of the microplage and of the matrix of the memory elements. They implement here the function SUP (A, B) or SUM (A, B) for a couple of a pixel of the microplage and of the corresponding pixel read in the screen memory, by line 11B. In the case of the SUP function (A, B), it is the pixel with the highest luminance which is rewritten in screen memory by the line 11A.

The operation of the processing unit 12 is of the random (synthetic image) or sequential (video image) type at input, and here, sequential at output. It could also be random at the output. It will be noted that the sequential display is particularly well suited to color matrix flat screens such as liquid crystal displays (LCD).

With reference to FIG. 6, the processing by micro-ranges comprises a step 24 of determining the addresses of the screen memory 10 followed by a step 25 of reading the memory, a step 26 of determining the parameters of selection of micro-range followed a step 27 of microplate generation and a step 28 of permutation, a step 29 of correlation according to the two steps 25 and 28, ending substantially at the same time, and preceding a step 30 of writing in the memory. As the processing unit 12 only processes points containing information, the presentation time of the images of the system which has just been described is not limited by the processing speed; it only depends on the speed of generation of the setpoints of the image generator 6. Thus, the seven steps 24-30, for a setpoint, are executed in the present example in 100 ns corresponding to the supply of the setpoint comprising the coordinates X, Y, color and fine position (half-pixel bits).

FIG. 7 shows the block diagram of the image processing chain of the device of the invention. The image generator 6 is connected to the microplate processing unit 12, the output of which is connected, via an interface 31 to the liquid crystal color screen 3. The processing unit is also connected to a generation of area code 32 controlled by a device 33 for detecting the orientation of the look of the observer. This detection device can be one of those described above. The output of the code generator device 32 is connected to the bus 8A (see FIG. 2).

• dialoguer avec le dispositif de détection de position 33, par exemple via une liaison informatique de type série 34, afin de recevoir des informations d'orientation du regard de l'observateur ;
• déterminer à partir de ces informations la zone de l'espace correspondante et en déduire le code de zone à transmettre ;
• transmettre ce code de zone à l'unité de traitement de microplages 12, par exemple via une liaison informatique de type parallèle 35 (reliée au bus 8A), ou directement sous forme de bits discrets.

The role of the area code generation device 32 is to:

• dialogue with the position detection device 33, for example via a computer link of the serial type 34, in order to receive information for orienting the gaze of the observer;
• determine from this information the zone of the corresponding space and deduce therefrom the zone code to be transmitted;
• transmit this area code to the microplate processing unit 12, for example via a parallel type computer link 35 (connected to the bus 8A), or directly in the form of discrete bits.

To make this device for generating area codes 32, one can simply use a microcomputer, for example of the PC type, on a serial port from which one of the position detection devices described above is connected, and of which a parallel port is connected to circuit 12. It then suffices to establish a simple microcomputer management program to make it fulfill the roles mentioned above and explained below.

The device 32 can also be produced using a dedicated computer, constructed for example from a microcontroller such as the 68HC11. A program transcribed in machine language and implanted in the read-only memory of the computer then makes it fulfill the same roles as in the aforementioned microcomputer.

We can consider that the microplate generator 8 (FIG. 2) of the unit 12 is composed of several "catalogs", each catalog being associated with a unique code coding the observation conditions of screen 3.

FIG. 8 shows the block diagram of such a dedicated computer (device 5 of FIG. 1). The microcontroller 36 is connected by the serial link 34 to the detector 33. Its address and data buses, referenced 37 as a whole, are connected to a program read-only memory 38, to an interface 39 and to a read-only memory containing a table or catalog of values of tangents of angles d observation and angles of angular limits. The output of the interface 39 is connected by the link 35 to the unit 12. The microcontroller 36 receives by the link 34, the coordinates of the sensor 33, will look in the memory 40 for the corresponding values of angles of observation (detailed below with reference to Figures 10 and 11), compare them to the angular limits (as explained below with reference to Figure 9) and deduce the corresponding area code.

In the case of the embodiment using a microcomputer, to constitute the unit 32, it is necessary to interpose between the unit 12 and this microcomputer an interface receiving from the latter the codes of observation conditions on a parallel computer link.

The unit 32 codes the viewing conditions of the screen as follows. We can consider the observation space as being a half-sphere in front of the screen plane. According to the invention, this hemisphere is cut into zones inside which the observer can be to look at the screen. It is assumed that within the same zone the observer has practically the same perception of the screen, whatever its position in this zone. We then associate with each zone a specific processing of the screen image. To simplify the coding, it is possible, for reasons of symmetry, to reduce the hemisphere to a quarter of hemisphere within which a horizontal angular border and a vertical angular border are defined.

We will expose below a simple example of coding associated with the different zones of a hemisphere.

There is shown in Figure 9 an example of cutting said hemisphere into elementary zones. The center of the LCD screen 3 is made to coincide with the origin O of the axes of a Cartesian space system Ox, Oy, Oz, the plane (xOy) being the plane of the screen and the drawing. The Oz axis is directed towards the top of the drawing, the Oy axis towards the right, and the Ox axis towards the viewer of the drawing and the screen. We have drawn on this figure the observation half-sphere 41 centered in O. On this half-sphere, we have drawn two horizontal or "parallel" angular limits 42 (with positive z-ordinate) and 43 (with negative z-ordinate) . The absolute value of the "latitude" of these angular limits is for example 45 °. On the other hand, vertical angular limits ("meridians") 44 (with positive x-axis) and 45 (with negative x-axis) have been drawn. The absolute value of the "longitude" of these limits is for example also 45 °. The planes (xOy), (yOz) and (zOx) cut this half-sphere into four quarters of a half-sphere. In each of these quarters, two of the corresponding angular limits determine four observation zones. Reference 46 is the 0 ° parallel of latitude ("equator") and 47 the meridian lying in the plane (Oz, Ox). We are going to examine for example the quarter of ½ sphere of which all the points have positive coordinates.

A first observation area, coded 00, is delimited by the limits 46, 47 and the limits 42 and 44. The second, coded 01 is delimited by 42, 44, 46 and the plane (yOz). The third, coded 10, is delimited by 44, 42 and 47. The fourth, coded 11, is the remaining zone, that is to say that delimited by 44, 42 and the plane (yOz). The determination of the zones for the other three quarters of a hemisphere is deduced by symmetry with respect to the plane (zOx) or (xOy).

Of course, the number of zones of the hemisphere is not necessarily four, and may be greater than this value. It can be adapted according to the measured performance of the screen, or according to the ambient conditions (temperature, brightness, ...), and / or according to the images displayed on the screen.

Thus, to code the direction of observation of screen 3, it suffices to connect the head (or the eye) of the observer in the center 0 of the screen and determine in which zone this straight line passes.

One can then draw up the table below, in which one understands by lower and upper limits the fact that the angular position of the observer is higher or lower than the considered limit. The codes are, of course, arbitrarily chosen.

Thus, for example for zone 01, the angular position of the observer is less (in absolute value) than the angular position of the horizontal limits 42, 43 (less than 45 ° for the aforementioned example), and is greater (in absolute value) at the angular position of the vertical limits 44, 45 (greater than 45 ° for the above example. Coded Vertical limit Horizontal boundary 00 lower lower 01 superior lower 10 lower superior 11 superior superior

Concretely, a position sensor 48 of one of the aforementioned types is fixed on the head of the observer, and the direction of observation is defined as a straight line connecting the position sensor to the center of the screen.

This line is the result of the intersection of two planes, a horizontal plane P1 called "azimuth" (rotation of the sensor around the axis 0z), defined by the line D "direction of observation" and the axis 0y, and a vertical plane P2 called "elevation" (rotation of the sensor around the axis 0y), defined by the right "direction of observation" and the axis 0z (FIG. 10).

The direction of observation is perfectly determined if we know how to measure two angles, an angle α defined as being the angular difference between the planes "elevation" and x0z, an angle β defined as the angular difference between the planes "azimuth and x0y.

A simple trigonometric calculation, starting from the x, y, z coordinates coming from the position sensor makes it possible to determine the angles α and β.

The angles α and β are calculated by projection of the position M of the sensor on the planes x0z (point Mv) and x0y (point Mh) (see Figure 11).

$$\text{β = ATAN (z/x)}$$

(ATAN étant la fonction arc tangente, et x, y z étant les coordonnées de la position de l'observateur dans le repère 0xyz.We thus determine: $$\text{α = ATAN (y / x)}$$

$$\text{β = ATAN (z / x)}$$

(ATAN being the tangent arc function, and x, yz being the coordinates of the position of the observer in the frame 0xyz.

These angles defining the direction of observation will make it possible, by comparison with the angular limits of the zones of space, to determine the code to be transmitted to the unit 12.

To determine the angular value of the zone limits, one can, at first, arbitrarily fix the angular limits of the zones at 45 °, and use sets of micro-ranges calculated from measurements of the electro-optical response of the display. , depending on the angle of view, in the horizontal and vertical planes.

The position of the limits can then be refined based on the results of an evaluation test, consisting in presenting on the display to a population of observers a test figure whose readability they will have to judge.

According to the above example, only two bits are used to code the observation conditions relating to the position of the user, thus defining four different zones of the observation space, and therefore four treatments (or sets of microplates). different.

A set of micro-ranges is composed for example of 1024 micro-ranges calculated as a function of the color to be generated, the characteristics of the display used, the definition of the image generator relative to that of the display.

A microplate is itself a polygon comprising several pixels, for example 1024.

FIG. 12 shows a simplified example (4x4 micro-ranges) of four micro-range zones corresponding to the above-mentioned four zones. The codes for these areas are as follows.

Code areas 00:

They correspond to an observation direction close to normal on the screen. In these regions, the response of the display is optimal, and the image will be processed to improve its quality (anti-aliasing, iridescence ...). In this case, a set of so-called "reference" microplates is used. The luminance levels of the various microplages of the microplage set have, according to their diagonals, a substantially Gaussian appearance.

Code areas 01:

The direction of observation deviates strongly from the normal on the screen in the horizontal plane. In this case, the display starts to have a degraded response (inversion of the contrast for shades of gray of low level, colorimetric drift). Visually, the apparent thickness of the displayed lines tends to decrease. It therefore becomes necessary, to ensure the readability of the image, to modify the treatment applied to it by using a set of microplates whose luminosity profile has been slightly enhanced.

Code areas 10:

The direction of observation deviates strongly from the normal on the screen in the vertical plane. As above, the display has problems displaying the images correctly. In practice, it is observed that the electro-optical response of an LCD screen is not symmetrical. The viewing angle is generally more closed in the vertical plane than in the horizontal plane. It is for this reason that the invented device allows different treatments for the horizontal and vertical planes.

For these zones, therefore, a set of moderately reinforced microplates is used.

Code areas 11:

The direction of observation deviates strongly from normal on the screen in both planes. In this most unfavorable case of observation, if one wants to ensure the legibility of the image it is necessary to use a set of saturated microplates (absence of gray level). The image quality is, of course, slightly degraded, but this is unimportant given the viewing conditions.

The device of the invention operates in real time. In fact, taking into account the observation conditions with regard to the direction of observation is only limited by the speed of the position detection system in measuring the position of the observer.

Thus, for the exemplary embodiment (LCD screen at 1024 x 1024 pixels, with QUAD distribution of the image points, and dynamic of sixteen luminance levels), the position of the observer is measured at the frequency of 30 Hz (i.e. every 33 ms), the calculation and transfer of the code to be applied to unit 12 is done in 1 ms, and the taking into account of a modification of the observation conditions by unit 12 is done at 100 Hz (i.e. every 10 ms).

It is thus seen that the device of the invention makes it possible to adapt the image to the observer in 1 / 30th of a second, which is sufficient even for rapid movement of the user.

Claims (6)

Method for optimizing the performance of a liquid crystal matrix screen (3) as a function of the observation angle, characterized in that it consists in dividing the observation space, represented by a half sphere, in front of the screen, in elementary zones corresponding to the different locations where the observer may be to look at the image, to associate a particular processing of the image to be presented on the screen with each zone, by determining for each zone, a set of microphages, themselves composed of several screen pixels, of which the luminance level of each pixel is determined experimentally, and the chrominance level of each microphage, as a function of the angle of observation , to obtain optimal readability, to memorize these values, then, in normal use, to detect the position of the observer relative to the screen, and to modify at least one of the image processing parameters to be presented on the screen according to the stored values and corresponding to the angle of observation detected. Method according to claim 1, characterized in that the elementary zones are delimited by vertical (44, 45) and horizontal (42, 43) angular limits. Method according to claim 2, characterized in that the position of the observer is determined relative to the screen using a sensor (1, 33, M) providing its coordinates in a Cartesian spatial reference , that these coordinates are converted into two angles: into angle (α) between a vertical plane normal to the screen at its center, and a vertical plane (P2) passing through the center of the screen and through the sensor, and a angle (β) between a horizontal plane normal to the screen at its center and a plane (P1) passing through the sensor and by a horizontal straight line (Oy) itself passing through the center of the screen, these angles defining the direction of observation, and comparing these angles with the angular limits of the elementary areas to determine the area corresponding to the position of the observer and control the treatment relating to this zone. Method according to one of the preceding claims, characterized in that one acts on at least one of the following parameters of the screen: luminance or chrominance. Device for optimizing the performance of a liquid crystal matrix screen, characterized in that it comprises a device (1, 33) for detecting the position of the observer (2) relative to the screen, connected by a processing device (5, 32) to a device (12) for weighting characteristics of the processing of the image to be presented on a liquid crystal screen (3), the processing device providing, from the information provided by the detection device, the data necessary for weighting. Device according to Claim 5, characterized in that the processing device comprises a computer (36) associated with a storage device (40) for trigonometric values and values for angular angle limits and with comparison means (38 ) providing an area code value.

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