WO2012155983A1

WO2012155983A1 - System for providing private viewing of multimedia contents of a display, and method thereof

Info

Publication number: WO2012155983A1
Application number: PCT/EP2011/058181
Authority: WO
Inventors: Ruiz Rodriguez Ezequiel
Original assignee: Naxos Finance Sa
Priority date: 2011-05-19
Filing date: 2011-05-19
Publication date: 2012-11-22
Also published as: EP2710581A1; EP2710581B1; ES2654200T3

Abstract

The present invention relates to a system (1) for providing private viewing of multimedia contents, said system (1) comprising: - a display (2) comprising a plurality of pixels; - an image signal generator (3) which generates an original image signal representative of an original image to be displayed on said display (2), said original image signal comprising Red, Green and Blue colour data components; - signal modifying means (4) which mix, on a pixel-by-pixel basis, each original image signal transmitted from the image signal generator (3) with at least one corresponding modifying image signal component thereof, in order to generate a compound image signal representative of a compound image; - extracting means (5) for extracting said original image from said compound image displayed on the display (2). The invention is characterized in that said system (1) further comprises: - a memory (6) apt to receive and record an original frame sequence (N, N+l, N+2) corresponding to the original image signal generated by said image signal generator (3) at a first speed (FC) corresponding to a clock frequency; - a duplicating element (7) apt to read said memory (6) at a second speed (2FC) corresponding to a speed which is the double of said clock frequency (FC), said duplicating element (7) being apt to duplicate said original frame sequence (N, N+l, N+2) in order to send to said signal modifying means (4) a first [2N, 2(N+1), 2(N+2)] and a second type of frame sequence [2N\ 2(N'+1), 2(N'+2)].

Description

SYSTEM FOR PROVIDING PRIVATE VIEWING OF MULTIMEDIA CONTENTS OF A DISPLAY, AND METHOD THEREOF

DESCRIPTION

The present invention relates to a system for providing private viewing of multimedia contents of a display according to the preamble of claim 1.

The present invention also relates to a method for providing private viewing of multimedia contents of a display.

Nowadays, with the massive use of video displays (such as, for example, those used in computer and televisions), there is a need to have a private viewing of multimedia contents displayed in said video displays, in such a way to allow viewing of said multimedia contents only by those who are authorized.

Therefore, a plurality of systems and methods for providing private viewing of multimedia contents of a display are known at the state of the art.

In particular, one of said systems comprises a display provided with a sort of shield that allows to restrict viewing of the display only to those positioned exactly in axis with said display; however, this system is not secure, since it cannot prevent viewing the display by a person positioned behind the user.

A second system provides to utilize an LCD display from which a polarizing layer has been removed, in order to render the display invisible to those don't wearing polarized glasses; however this system is not versatile, since it is only apt to be used on the LCD displays.

Another system for providing private viewing of multimedia contents of a display foresees to combine, to a first image having a certain wavelength, a second image having a different wavelength; the use of narrow-band filtered glasses allows to see the first image in a proper way. However, this system has many drawbacks, and in particular it allows to anyone wearing said narrow-band filtered glasses to see the multimedia content displayed on the display.

A further system for providing private viewing of multimedia contents of a display provides to introduce some mask pattern or maslcing text characters into a sequence of images, and to intercept the disturbing image through the use of LCD shutter glasses; this system requires the use of an additional light screen, that inevitably implies the consumption of additional power.

Moreover, are known at the state of the art other systems for providing private viewing of multimedia contents of a display, in particular said systems comprising an image signal generator which generates an original image signal representative of an original image to be displayed.

The original image signal comprises Red, Green and Blue colour data components; each of said RGB colour data components is transmitted from the image signal generator to signal modifying means, where it is mixed or multiplexed on a pixel-by-pixel basis with at least one corresponding modifying (inverse and/or complementary) colour data component thereof.

Such a mixing or multiplexing is done at such a frequency that the human brain only interprets the composition of original colour components and modifying (inverse and/or complementary) colour components generated thereby as a single compound mixed image, which is substantially neutral and featureless.

A sync control element is associated both to the signal modifying means, both to special eyewear, in order to decode and extract the original image from the single compound mixed image; preferably, said special eyewear comprises time-synchronized LCD shutters, variable polarizers or similar synchronized filters, that selectively block the modifying (inverse and/or complementary) colour components of the resulting compound mixed image, thus allowing only the original image to pass.

Therefore, the system previously described permits to a user a private viewing of multimedia contents.

However, it has been observed that also the system previously described suffers from some drawbacks.

In particular, it does not allow to have a sufficiently good quality of the original image arriving to the user; in fact, in the system previously described, the frequency of the original image signal representative of an original image to be displayed is reduced of the 50%, with the consequent introduction of visible display flicker, which is very annoying and disturbing for a user.

Moreover, being said frequency of the original image signal reduced, the display of motion pictures and scenes does not result in a motion depiction in which the depicted objects move smoothly and correctly, but said display of motion pictures is jerky, not continuous and sometimes difficult to follow.

Again, in the system previously described, the original colour data components and the modifying (inverse and/or complementary) colour data components corresponding to each pixel are multiplexed alternately in time over the respective frame periods "n" and "n+1". It is therefore clear that, when the image relates to a motion picture or scene, the pixels of the frame period "n" are not the same of the pixels of the frame period "n+1". Thus, the pixels of the modifying image are not in the position to neutralize and obscure the pixels of the original image; it is therefore clear that this system is not secure and eclectic, since it cannot be used for providing private viewing of multimedia contents relating to motion pictures and scenes.

In this frame, it is the main object of the present invention to overcome the above- mentioned drawbacks by providing a system and a method for providing private viewing of multimedia contents of a display, which allow to prevent in a secure way unauthorized persons to view said multimedia contents.

It is a further object of the present invention to provide a system and a method for providing private viewing of multimedia contents of a display conceived in a manner to be versatile and eclectic, since they are apt to be used in each type of screen or display and also for providing private viewing of multimedia contents relating to motion pictures and scenes.

Another object of the present invention is to provide a system and a method for providing private viewing of multimedia contents of a display able to eliminate any display flicker and jerky images, in such a way to display an image of good quality. These objects are achieved by the present invention through a system and a method for providing private viewing of multimedia contents of a display, incorporating the features set out in the appended claims, which are intended as an integral part of the present description.

Further objects, features and advantages of the present invention will become apparent from the following detailed description and from the annexed drawings, which are supplied by way of non-limiting example, wherein: - Fig. 1 represents a block diagram of a system for providing private viewing of multimedia contents of a display according to the present invention;

- Fig. 2 represent a portion of the system represented in Fig. 1 ;

- Fig. 3 represents a display sequence of a Red colour data component according to the system represented in Fig. 1.

In Fig. 1, reference numeral 1 designates as a whole a system for providing private viewing of multimedia contents of a display according to the present invention.

The system 1 according to the exemplary embodiment of the present invention comprises a display 2 comprising a plurality of pixels and an image signal generator 3 which generates an original image signal representative of an original image to be displayed on said display 2.

The original image signal comprises Red, Green and Blue colour data components, which are output from said image signal generator 3 along lines 31R, 31G and 3 IB respectively.

It must be noted that substantially all known video displays generate an image through the mixture of three primary colours of light, i.e. Red, Green and Blue, in particular by means of a plurality of pixels comprised in the display 2. In fact, human eyes do not detect separately each Red, Green, Blue pixel comprised on the display 2, but a user viewing the display 2 will see a range of many colours combined to produce a desired image. Moreover, if the intensities of all Red, Green and Blue components of a given pixel are substantially the same, that pixel will produce a neutral white light.

Said system 1 further comprises signal modifying means 4 which mix, on a pixel-by- pixel basis, each original image signal transmitted from the image signal generator 3 with at least one corresponding modifying image signal component thereof, in order to generate a compound image signal representative of a compound image.

It is clear that said signal modifying means 4 may mix each of said RGB colour data components (original colour data components) of the original image signal transmitted from the image signal generator 3 with at least one modifying (i.e. inverse and/or complementary) colour data component thereof.

In this respect, it must be noted that the "inverse" of a colour is not a synonymous of "complementary" of a colour. In fact, two colours are called complementary if, when mixed in the proper proportion, for instance in a scale of 256 bits, they produce a neutral color (grey, white, or black). On the contrary, an inverse colour is calculated by subtracting each component of an RGB colour from 255; therefore the result of the mixing, on a pixel-by-pixel basis, of an original image signal with a corresponding inverse image signal is a compound mixed image that appears substantially neutral and featureless.

Moreover, said system 1 comprises extracting means 5 for extracting said original image from said compound image displayed on the display 2.

In particular, said extracting means 5 may provide for specialized eyewear comprising synchronized LCD shutter, polarizers, colour filters, or similar means apt to selectively block the inverse and/or complementary colour components of the compound mixed image, in such a way to allow only the extraction of the original image from said compound mixed image.

In accordance with the present invention, said system 1 comprises:

- a memory 6 apt to receive and record an original frame sequence corresponding to the original image signal generated by said image signal generator 3 at a first speed FC corresponding to a clock frequency;

- a duplicating element 7 apt to read said memory 6 at a second speed 2FC corresponding to a double of said clock frequency FC, said duplicating element 7 being apt to duplicate said original frame sequence in order to send to said signal modifying means 4 a first and a second type of frame sequence.

As it is clearly represented in Fig. 1, said memory 6 comprises:

- a first portion 6R apt to receive and record a Red colour data component of the original image signal;

- a second portion 6G apt to receive and record a Green colour data component of the original image signal;

- a third portion 6B apt to receive and record a Blue colour data component of the original image signal.

Each portion 6R, 6G, 6B of memory 6 comprises two frame stores 6A and 6B, in particular a first frame store 6A and a second frame store 6B (see Fig. 2, that represents a first portion 6R, 6G, 6B of the memory 6). The two frame stores 6A and 6B work in a "flip-flop" manner, namely, if during frame n the first frame store 6 A is written, the second frame store 6B is read; during frame n+1 the reverse happens, namely the first frame store 6A is read and the second frame store 6B is written.

The two frame stores 6A and 6B are read at a double speed, namely at a second speed 2FC corresponding to a speed which is the double of the speed of the clock frequency FC.

The output video reproduces the input video, with one frame delay and with each frame duplicated; thus, if the input video has a vertical frequency FV, the output video has a double vertical frequency 2FV, i.e. a period having a speed which is the double of the speed of the vertical frequency FV.

The output video can be considered as the interleaving of two frame sequences (identical to the input frame sequence, apart from the delay), respectively called "first and second type of frame sequences".

Preferably, said signal modifying means 4 comprise:

- a plurality of first multiplexers 41R, 41G, 4 IB, each of said first multiplexers 41R, 41G, 41B being apt to receive said first and second type of frame sequences of one of said Red, Green and Blue colour data components;

- a plurality of complementing circuits 42R, 42G, 42B, each of said complementing circuits 42R, 42G, 42B being associated to a respective first multiplexer 41R, 41G,

41B for elaborating said second type of frame sequence and producing a third type of frame sequence corresponding to a modifying (i.e. inverse and/or complementary) colour data component;

- a plurality of second multiplexers 43R, 43G, 43B, each of said second multiplexers 43R, 43 G, 43B being associated to a respective first multiplexer 41R, 41G, 41 B for receiving said first type of frame sequence, and to a respective complementing circuits 42R, 42G, 42B for receiving said third type of frame sequence, in order to send to the display 2 a compound mixed image that is representative of said first and third type of frame sequence and results to be substantially neutral and featureless. As it can be seen from Fig. 1, each multiplexer 41R, 41G, 4 IB of said plurality of first multiplexers 41R, 41G, 41B is respectively associated to said first 6R, second 6G and third portion 6B of the memory 6 by means of respective second lines 61R, 61G and 61B; therefore, each of said first multiplexers 41R, 41G, 41B is apt to receive said first and second type of frame sequences from said first 6R, second 6G and third portion 6B respectively.

Moreover, each multiplexer 43R, 43G, 43B of said plurality of second multiplexers 43 R, 43 G, 43 B is respectively associated to said display 2 by means of respective third lines 44R, 44G and 44B; therefore, said display 2 is apt to receive said first and third type of frame sequences from each of said second multiplexers 43R, 43G, 43B.

Thus, for any given pixel of the display 2, the relative display sequence may be represented as shown in Fig. 3, that relates to the display sequence of the Red colour data component; however, it is clear that the display sequence of the Green and Blue colour data components will have a totally similar behaviour of the Red colour data component represented in Fig. 3.

In particular, in Fig. 3 it is shown that the input side (indicated in line 1 of Fig. 3 with the reference 6R-IN and in line 2 of Fig. 3 with the references 31R or 6R-IN) of the first portion 6R receives a Red colour data component of the original image signal at a first speed FC corresponding to a clock frequency, and records at least an original frame sequence (indicated in line 2 of Fig. 3 with references N, N+l, N+2, ...).

Duplicating element 7 reads said first portion 6R of the memory 6 at a second speed 2FC corresponding to a speed which is the double of the speed of said clock frequency FC, in such a way to duplicate said original frame sequence (N, N+l, N+2) and to obtain, at the output (indicated in line 4 of Fig. 3 with reference 6R-OUT) of the first portion 6R, a sequence containing a first type of frame sequence (designated in Fig. 3 as 2N, 2(N+1), 2(N+2), ...) and a second type of frame sequence (designated in Fig. 3 as 2N', 2(N'+1), 2(N'+2), ...), in particular in a period corresponding to a Vertical Frequency FV.

Said first [2N, 2(N+1), 2(N+2)] and second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] have the same content of the original frame sequence (N, N+l, N+2); in particular, said second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] is outputted from said first portion 6R of the memory 6 by the duplicating element 7 with a delay of a period corresponding to a double Vertical Frequency 2FV with respect to said first type of frame sequence [2N, 2(N+1), 2(N+2)], i.e. of a period having a speed which is the double of the speed of the original Vertical Frequency FV (see line 3 of Fig. 3). It is therefore clear that said first [2N, 2(N+1), 2(N+2)] and second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] substantially correspond to said original frame sequence (N, N+l, N+2) and are obtained by the duplicating element 7, that reads said first portion 6R of the memory 6 at a second speed 2FC that corresponds to the double of the speed of said clock frequency FC

The first multiplexer 41R is controlled at a speed corresponding to said double Vertical Frequency 2FV and deviates:

- the first type of frame sequence [2N, 2(N+1), 2( +2)] towards an input side (designated in Fig. 3 as 43R-IN) of the second multiplexer 43R;

- the second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] towards an input side (designated in Fig. 3 as 42R-IN) of the complementing circuits 42R, in particular with a delay of a period corresponding to a double Vertical Frequency 2FV.

Said complementing circuit 42R transforms said second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] producing a third type of frame sequence (designated in Fig. 3 as 2N*, 2(N*+1), 2(N*+2), ...) corresponding to a modifying (i.e. inverse and/or complementary) colour data component of the Red colour data component received from the first multiplexer 41R.

In particular, according to the present invention, said complementing circuit 42R produces an inverse colour data component, subtracting from the level 255 the Red colour data component received from the first multiplexer 41R; in other words, the complementing circuit 42R executes the complement at 255 of the sequence of all the Red colour data components received at 8 bits related to the second type of frame sequence [2N'₃ 2(N'+1), 2(N'+2)], in order to produce a third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] representative of an inverse colour data component, corresponding to a modifying image signal.

Also the second multiplexer 43 R is controlled at a speed corresponding to said double Vertical Frequency 2FV and deviates both the first type of frame sequence [2N, 2(N+1), 2(N+2)] and both the third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] toward an output side (designated in line 8 of Fig. 3 as 43R-OUT or 44R) of the second multiplexer 43R and toward the display 2; in particular, the second multiplexer 43R is controlled in such a way that said third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] is deviated toward the display 2 with a delay of a period corresponding to a double Vertical Frequency 2FV with respect to said first type of frame sequence [2N, 2(N+1), 2(N+2)].

It is therefore clear that the display 2 will produce a compound image, i.e. an image that is the result of the addiction of:

- original image signals representative of an original image [i.e. signals of the first type of frame sequence [2N, 2(N+1), 2(N+2)], said first type of frame sequence [2N, 2(N+1), 2(N+2)] having the same content of the original frame sequence (N, N+l, N+2)] and

- modifying image signals representative of a modified image (i.e. signals of the third type of frame sequence [2N*, 2(N*+1), 2(N*+2)]),

in particular said original image and said modifying image being alternated at a speed corresponding to a double Vertical Frequency 2FV in order to produce said compound image.

From Fig. 1 it can be also seen that the duplicating element 7 receives an Horizontal Frequency FH from the image signal generator 3, and sends to the display 2 a second Horizontal Frequency 2FH having a frequency which is the double of the frequency of said Horizontal Frequency FH.

Preferably, said extracting means 5 are associated with the duplicating element 7, in particular through a control line 51 ; thus, the shutter speed of the extracting means 5 is synchronized with the mixing speed imparted from said duplicating element 7, in particular said mixing speed corresponding to a double Vertical Frequency 2FV. The manner to synchronize the shutter speed of the extracting means 5 may be of various type; for instance using a wireless connection based on infrared technology or radio ones, like the Bluetooth.

In this way, upon viewing the display 2 by means of said extracting means 5, the modifying (inverse and/or complementary) colour data component of the compound image are blocked from view, thereby allowing passage only of the original colour components representative of the original image to be displayed. In fact, as it can be seen also from line 9 of Fig. 3, said extracting means 5 allow the passage only of the first type of frame sequence [2N, 2(N+1), 2(N+2)] that has the same content and the same repetition speed (for example, 50Hz) of the original frame sequence (N, N+l, N+2); therefore, thanks to the provisions of the present invention, it is possible to maintain unaltered (without any display flicker and jerky images) the content of multimedia contents, even if said contents relate to motion pictures and scenes.

On the contrary, a person who is not allowed to use said extracting means 5, he is only in the position to see the compound or mixed image that appears on the display 2, said compound or mixed image resulting from the view of both the first type of frame sequence [2N, 2(N+1), 2(N+2)], both the third type of frame sequence [2N*, 2(N*+1), 2(N*+2)], as it can be see also from line 8 of Fig. 3; it is therefore clear that said compound or mixed image results neutral and featureless.

In a preferred embodiment of the present invention, said extracting means 5 may comprise input means (not shown in Fig. 1) for inputting an access code prior to use, in such a way to further enhance the security level of the system 1.

The advantages offered by an system and a method for providing private viewing of multimedia contents of a display according to the present invention are apparent from the above description.

In particular, such advantages are due to the fact that the system and a method according to the present invention allow to prevent, in a secure way, unauthorized persons to view multimedia contents of a display.

Moreover, the system and method according to the present invention are conceived in a manner to be versatile and eclectic, since they are apt to be used in each type of screen or display and also for providing private viewing of multimedia contents relating to motion pictures and scenes.

In fact, the provision of:

- a memory 6, which is apt to receive and record an original frame sequence corresponding to the original image signal generated by said image signal generator 3;

- a duplicating element 7, which is apt to read said memory 6 at a second speed 2FC corresponding to a double of said clock frequency FC and to duplicate said original frame sequence in order to and to send to said signal modifying means 4 a first and a second sequence of said original image signal,

allow to indicate a system and a method able to eliminate any display flicker and jerlcy images.

Therefore, the system and the method according to the present invention allow to display an image of good quality.

The system and method described herein by way of example may be subject to many possible variations without departing from the novelty spirit of the inventive idea; it is also clear that in the practical implementation of the invention the illustrated details may have different devices or be replaced with other technically equivalent elements, as well as providing different sequences of steps.

It can therefore be easily understood that the present invention is not limited to the above-described system and method, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.

Claims

1. System (1) for providing private viewing of multimedia contents, said system (1) comprising:

- a display (2) comprising a plurality of pixels;

- an image signal generator (3) which generates an original image signal representative of an original image to be displayed on said display (2), said original image signal comprising Red, Green and Blue colour data components;

- signal modifying means (4) which mix, on a pixel-by-pixel basis, each original image signal transmitted from the image signal generator (3) with at least one corresponding modifying image signal component thereof, in order to generate a compound image signal representative of a compound image;

- extracting means (5) for extracting said original image from said compound image displayed on the display (2);

characterized in that

said system (1) further comprises:

- a memory (6) apt to receive and record an original frame sequence (N, N+l, N+2) corresponding to the original image signal generated by said image signal generator

(3) at a first speed (FC) corresponding to a clock frequency;

- a duplicating element (7) apt to read said memory (6) at a second speed (2FC) corresponding to a speed which is the double of said clock frequency (FC), said duplicating element (7) being apt to duplicate said original frame sequence (N, N+l, N+2) in order to send to said signal modifying means (4) a first [2N, 2(N+1), 2(N+2)] and a second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)].

2. System (1) according to claim 1, characterized in that said memory (6) comprises:

- a first portion (6R) apt to receive and record a Red colour data component of the original image signal;

- a second portion (6G) apt to receive and record a Green colour data component of the original image signal;

- a third portion (6B) apt to receive and record a Blue colour data component of the original image signal.

3. System (1) according to one or more of the preceding claims, characterized in that said signal modifying means (4) comprise a plurality of first multiplexers (41R, 41G, 4 IB), each of said first multiplexers (41R, 41G, 4 IB) being apt to receive said first [2N, 2(N+1), 2(N+2)] and second type of frame sequences [2Ν', 2(N'+1), 2(N'+2)] of one of said Red, Green and Blue colour data components.

4. System (1) according to claim 4, characterized in that said signal modifying means (4) comprise a plurality of complementing circuits (42R, 42G, 42B), each of said complementing circuits (42R, 42G, 42B) being associated to a respective first multiplexer (41R, 41G, 4 IB) for elaborating said second type of frame sequence [2N\ 2(N'+1), 2(N'+2)] received from the respective first multiplexer (41R, 41G, 41B) and producing a third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] corresponding to a modifying colour data component.

5. System (1) according to claim 4, characterized in that said signal modifying means (4) comprise a plurality of second multiplexers (43R, 43G, 43B), each of said second multiplexers (43 R, 43 G, 43 B) being associated to a respective first multiplexer (41R, 41G, 4 IB) for receiving said first type of frame sequence [2N, 2(N+1), 2(N+2)], and to a respective complementing circuits (42R, 42G, 42B) for receiving a respective third type of frame sequence [2N*, 2(N*+1), 2(N*+2)], in order to send to the display (2) a compound mixed image that is representative of said first [2N, 2(N+1), 2(N+2)] and third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] and results to be substantially neutral and featureless.

6. System (1) according to one or more of the preceding claims, characterized in that said extracting means (5) are associated to the duplicating element (7) through a control line (51), the shutter speed of said extracting means (5) being synchronized with the mixing speed imparted from said duplicating element (7), in particular said mixing speed corresponding to a double Vertical Frequency (2FV).

7. System (1) according to claim 6, characterized in that it comprises a wireless connection based on infrared technology or radio ones for synchronizing the shutter speed of the extracting means (5) with the mixing speed imparted from said duplicating element (7).

8. System (1) according to one or more of the preceding claims, characterized in that said extracting means (5) comprise input means for inputting an access code prior to use.

9. Method for providing private viewing of multimedia contents of a display (2), said method comprising the following steps:

a) generating an original image signal representative of an original image to be displayed on said display (2) by means of an image signal generator (3), said original image signal comprising Red, Green and Blue colour data components;

b) activating signal modifying means (4) for mixing, on a pixel-by-pixel basis, each original image signal received from the image signal generator (3) with at least one corresponding modifying image signal component thereof, in order to generate a compound image signal representative of a compound image;

c) extracting said original image from said compound image displayed on the display (2) by means of extracting means (5),

characterized in that

said step b) is preceded by the steps of:

d) receiving in a memory (6) said Red, Green and Blue colour components of the original image signal generated by said image signal generator (3) at a first speed (FC) corresponding to a clock frequency, and recording in said memory (6) at least an original frame sequence (N, N+1, N+2) corresponding to said original image signal; e) activating a duplicating element (7) for reading said memory (6) at a second speed (2FC) corresponding to a speed which is the double of said clock frequency (FC) and for duplicate said original frame sequence (N, N+1, N+2) in order to send to said signal modifying means (4) a first type of frame sequence [2N, 2(N+1), 2(N+2)] and a second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)], in particular in a period corresponding to a Vertical Frequency (FV).

10. Method according to claim 9, characterized in that said step e) is performed by activating said duplicating element (7) in such a way that said first [2N, 2(N+1), 2(N+2)] and second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] have the same content of the original frame sequence (N, N+1, N+2), in particular said second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] being outputted from said memory (6) with a delay of a period corresponding to a double Vertical Frequency (2FV) with respect to said first type of frame sequence [2N, 2(N+1), 2(N+2)].

11. Method according to one or more of previous claims 9 and 10, characterized in that said step b) is actuated by means of a plurality of first multiplexers (41R, 41G, 4 IB) which are controlled at a speed corresponding to said double Vertical Frequency (2FV) in order to deviate:

- the first type of frame sequence [2N, 2(N+1), 2(N+2)] towards an input side of a plurality of second multiplexers (43R, 43G, 43B);

- the second type of frame sequence [2N\ 2(N'+1), 2(N'+2)] towards an input side of a plurality of complementing circuits (42R, 42G, 42B), in particular with a delay of a period corresponding to a double Vertical Frequency (2FV).

12. Method according to claim 11, characterized in that it further comprises the step of activating said plurality of complementing circuits (42R, 42G, 42B) for transforming said second type of frame sequence [2Ν', 2(N'+1), 2(N'+2)] and producing a third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] corresponding to a modifying colour data component of the Red, Green and Blue colour data components received from said plurality of first multiplexers (41R, 41G, 41B).

13. Method according to claim 12, characterized in that said plurality of complementing circuits (42R, 42G, 42B) is activated for producing an inverse colour data component.

14. Method according to one or more of the previous claims from 9 to 13, characterized in that it further comprises the step of controlling said plurality of second multiplexers (43R, 43G, 43B) at a speed corresponding to said double Vertical Frequency (2FV) for deviating said first type of frame sequence [2N, 2(N+1), 2(N+2)] and said third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] toward the display (2).

15. Method according to claim 14, characterized in that said plurality of second multiplexers (43R, 43G, 43B) are controlled in such a way that said third type of frame sequence [2N*, 2(N*+1), 2(N*+2)] is deviated toward the display (2) with a delay of a period corresponding to a double Vertical Frequency (2FV) with respect to said first type of frame sequence [2N, 2(N+1), 2(N+2)].

16. Method according to claims 9, characterized in that said step c) is performed associating said extracting means (5) with the duplicating element (7), in particular through a control line (51), in order to synchronize the extracting means (5) with said duplicating element (7).