WO2009043857A1

WO2009043857A1 - System for displaying images with four primary colours from video data based on three primary colours

Info

Publication number: WO2009043857A1
Application number: PCT/EP2008/063107
Authority: WO
Inventors: Sylvain Thiebaud; Jean-Ronan Vigouroux; Pascal Bourdon
Original assignee: Thomson Licensing
Priority date: 2007-10-01
Filing date: 2008-09-30
Publication date: 2009-04-09
Also published as: FR2921785A1

Abstract

The invention relates to a video image display system capable of displaying video images with four primary colours from video data based on three primary colours. The system is particularly useful for preventing the copy of films using camcorders in cinema theatres. According to the invention, the system includes a circuit (100) for converting first video data (Rin, Vin, Bin) of an image pixel based on three colour components, or first colour components, into second video data (Rout, Vout, Bout, Jout) based on said three first colour components and an additional component (Jout), the value of the additional component (Jout) of said second video data being different from zero, and a display device (110; 111, 112) for displaying said second video data. The conversion device (100) includes several conversion blocks for the real-time conversion of video data.

Description

SYSTEM FOR DISPLAYING IMAGES WITH FOUR PRIMARY COLORS FROM VIDEO DATA BASED ON THREE

PRIMARY COLORS

Field of the invention

The present invention relates to a display system capable of displaying images with four primary colors from video data based on three primary colors. This system is particularly used to prevent copying of movies using camcorders in theaters.

Technological background of the invention

The patent application WO 2004/040899 discloses techniques for modifying, in an imperceptible manner for the human eye, the spectrum of the images displayed by a video projector so as to discourage the copying of the images by means of a camcorder. The modification of the spectrum is obtained by the use of a fourth primary color component. This fourth component ("or fourth primary") allows the creation of spectra having different spectral compositions but inducing the same perception of light and colorimetric by the human eye. Such spectra exist for each color because the human eye uses only three types of receptors (or cones) to create the colorimetric sensation associated with a light. Spectra producing identical effects on the three types of receptors appear identical to the eye without necessarily being spectrally identical. Such spectra are then called metamers. We also speak of metameric colors or metameric mixtures.

Because camcorders typically have RGB light receivers (for Red, Green, Blue) that are noticeably different from those in the human eye, metameric spectra for the human eye are not necessarily for the camcorder and may appear as different in chrominance or in luminance on the copy filmed by the camcorder. This effect is then used to insert tattoos or copy-proofing patterns in images projected in cinemas to degrade the quality of copies made by a camcorder and possibly to know the origin of copies. The anti-copy pattern is for example a message indicating that the film is an illicit copy or a code identifying the film that was copied or the movie theater that screened the film. If the anti-copy pattern is inserted into a portion of the uniform color image, it is for example displayed using a first mixture of primary colors and the remainder of the uniform color image portion is displayed using a second mixture of primary colors, these two mixtures being metamers. For the anti-copy motif to be as visible as possible on the illicit copy, the first mixture is advantageously a mixture in which the fourth primary color component is maximum and the second mixture is a mixture in which the fourth primary color component is nothing. The implementation of this display technique requires the use of a four-color primary digital cinema projector or two digital projectors, one displaying three primary colors and the other displaying the fourth primary. In the following description, we will speak more generally of display system. The four primary colors are for example red, green and blue and a fourth primary color that is different from the other three. This fourth primer is for example obtained by partially filtering the light from the red, green and blue light source of a conventional projector. On the other hand, since the video signal supplied to the display system is based on the three primary red, green and blue color components, it must be transformed to generate a four-component signal. Patent application WO 2004/040899 describes a method for generating the four primary color components from the three-component signal received by the projector, but the method presented in this document is very complex to implement and difficult to apply in time. real. Document US2005 / 099426 teaches how, through a subtractive step also used in the invention, to transform first video data based on three first color components into second video data based on said first three color components and a component of color. additional color, where the additional color component is non-zero. However, the process described in this document does not make it possible to optimize at best a metameralization effect. SUMMARY OF THE INVENTION An object of the invention is therefore to provide a method and a video image display system in which the three color component video data present at the input of the system are transformed in real time into data. video based on four color components, in particular, to optimize the effect of metamerization. The invention relates to a video image display method in which each pixel is represented by first video data based on three first color components, using a display device controllable using second data. video based on said first three color components and an additional color component, wherein said first video data of at least one pixel of said video image is transformed into second video data where the additional color component is non-zero according to the following steps :

by using a first transformation, transforming said first video data of the at least one pixel into first colorimetric coordinates expressed in a linear color space;

a non-zero value of said additional color component of said second video data of the at least one pixel is determined according to said first colorimetric coordinates; - using a second transformation, transforming said additional color component value into second coordinates colorimetrically in said linear color space;

by subtracting said second colorimetric coordinates from said first colorimetric coordinates, third colorimetric coordinates are generated in said linear color space, which correspond to a so-called "remaining" color;

using a third inverse transformation of the first transformation, transforming said third colorimetric coordinates into values of said first three color components of said second video data of the at least one pixel, wherein said value of the color component; additional is determined to be maximum and so that the corresponding "remaining" color is actually displayable by the display device without using said additional color component. Preferably, said linear color space is independent of any display device. One can choose in particular space CIE XYZ.

Preferably, the set of pixels for which, according to said steps, the first video data in second video data is transformed into an anti-copy pattern inserted in the said video image. In other words, each image to be displayed is divided into two zones: a pattern area of which all the pixels are affected by the steps of the method according to the invention, and a non-pattern area where no pixel is affected. In other words, for the display of an image, the out-of-pattern area will be displayed using only the first three color components, while the area of the pattern will be displayed using, in addition to the first three color components, the additional component. of color. Thanks to the invention, an optimized metameric effect is obtained.

The invention also relates to a video image display system comprising:

a circuit for transforming first video data of an image pixel based on three color components, called first color components, into second video data based on said first three color components and an additional component, the value of the additional component of said second video data being non-zero,

a display device for displaying said second video data, said system being remarkable in that said transformation circuit comprises:

a first block for transforming said first video data into colorimetric coordinates, called first colorimetric coordinates, in a color space independent of any display device,

a second block for determining, based on said first colorimetric coordinates, the value of the additional color component of said second video data; a third block for transforming said additional color component value into second colorimetric coordinates in said color space; ,

a fourth block for subtracting the second color coordinates from said first colorimetric coordinates and generating third color coordinates in said color space, and

a fifth block for transforming said third colorimetric coordinates into values based on said first three primary color components, said first color component values being the values based on said first three color components of the second video data.

Preferably, the color space independent of any display device is linear.

Preferably, the value of the additional color component of said second video data determined by the second block is the highest possible value which nevertheless allows the display of the remaining color represented by the third color coordinates by the device. display without using the additional color component (or by using an additional null color component). The remaining color should be in the color gamut of the additional color non-component display. Thus, if the system is used to display an anti-copy pattern, this pattern can be advantageously rendered as visible as possible.

The second block advantageously comprises a conversion table or look-up table in the English language. Thus, all the blocks of the transformation circuit permit a real-time transformation of the three color component signal into a four color component signal.

In the context of a system able to display anti-copy patterns, the system further comprises a transformation authorization circuit inserted between the second block and the third block, said transformation authorization circuit receiving as input the value of the additional color component determined by the second block and a binary information allowing or not the transformation of the first video data into the second video data, which circuit delivers said value of the additional color component if said binary information authorizes the transformation and a value none otherwise. The binary information is, for example, information authorizing the transformation when the current pixel belongs to an anti-copy pattern to be inserted in the video image. Thus, when the current pixel belongs to the anti-copy pattern, the pixel is displayed with four primary colors and, if not, the pixel is displayed with three primary colors (the fourth primary color component being zero).

Brief description of the figures

The invention will be better understood on reading the description which will follow, given by way of nonlimiting example, and with reference to the appended drawings among which: FIG. 1 is a general diagram of a first video image display system according to the invention,

FIG. 2 is a general diagram of a second video image display system according to the invention, and FIG. 3 is a detailed diagram of the transformation circuit of the display system of FIG. 1 or 2; .

Figure 1 illustrates the diagram of a first display system 10 according to the invention. This display system 10 comprises a transformation circuit 100 for transforming first video data R _1n , V _1n , B _1n of an image pixel, based on three color components, called first color components, in seconds. R _or t video data, V ₀ Ut, B ₀ Ut, Jout, based on said first three color components and an additional color component. Thus, the three primary color components of the video signal present at the input of the display system 10 are transformed into a signal with 4 primary color components. The system 10 also comprises a digital projector 110 connected to the outputs of the transformation circuit 100. This projector 110 is said to be quadriprimary since it makes it possible to display four primary color components. The transformation circuit 100 receives as input a video signal comprising a red component R _1n , a green component V _1n and a blue component B _1n and outputs a video signal comprising a red component R _or t, a green component V _or t a blue component B ₀ Ut and an additional primary color component J _or t- The primary color associated with the additional component is different from the other three primary colors. The four components R _or t, V _or t, B _or t and J _or t are displayed by the projector 110. The projector 110 is for example a DLP projector (for Digital Light Processing in English or digital light processing) or any display device capable of displaying more than three primary colors. Figure 2 illustrates the diagram of a second display system 10 according to the invention. This diagram differs from that of FIG. 1 in that the four-pry projector 110 is replaced by two digital projectors 111 and 112. The components R _or t, V _or t, B _out delivered by the transformation circuit 100 are displayed by the projector 111 and the component J _or t is displayed by the projector 112. The additional primary color associated with the component J _or t is for example obtained by filtering the light source of the projector 112. This additional primary color is for example a yellow, a cyan blue, a deep red, a magenta red or a green different from the green of the light source. The two digital projectors used are, for example, DLP projectors (for Digital Light Processing in English or digital light processing) or any display device capable of displaying more than three primary colors.

The first video data R _1n , V _1n , B _1n at the input of the transformation circuit 100 represent the color of an image pixel to be displayed in the linear color space linked to the projector 111. This same color can also be represented by colorimetric coordinates in a color space independent of the display device (or "device-independent" in English) such as the XYZ space defined by the International Commission on Illumination (CIE). The second video data R ₀ Ut, V ₀ Ut, B ₀ Ut, Jout provided at the output of the transformation circuit 100 also represent the same color in the color space associated with the four-prong projector 110 or the set formed by the projector 111 and the projector 112. In the case of Figure 2, the components R _or t, V _or t, B _out are provided to the projector 111 and the component J _or t is supplied to the projector 112. In practice, the components R _or t, V _or t, B _out are respectively applied to the video inputs R, V, B of the projector 111 and the component J _or t is applied simultaneously to the three inputs R, V, B of the projector 112. It should be noted that we could consider posting differently, the two primary colors being displayed by the projector 111 and two other primary colors being displayed by the projector 112.

The transformation circuit 100 is responsible for calculating in real time the four color components R _out , V _or t, B _or t, Jout from the three color components R _1n , V _1n , B _1n . The transformation performed by the circuit 100 is performed in a linear domain. That is why the components R _1n , V _1n and B _1n supplied to the circuit 100 should be linear, which is the case if the color space associated with the projector 111 is linear. Consequently, if this were not the case, an additional transformation would be applied previously to the components R _1n , V _1n and B _1n to make them linear and an inverse transformation would be applied later on the components R _or t, V _or t, B _out and J _out . This additional transformation is for example a gamma correction.

In the following description and for the sake of clarity, the invention will be more particularly described in the context of a display system with two projectors 111, 112 as shown in Figure 2, without it being possible to see a any limitation of the scope of the invention to this embodiment.

The color generated by the projector 111 when it receives as input the components R _or t, V _or t, B _out can be defined as follows: outl XR K XV K outl YR K YV K

^J ZR K ZV K

Cl outl The matrix column outl represents, in the XYZ color space, the

^J outl color generated by the projector 111 when it receives the R component _or t, V ₀ Ut, Ut B ₀ and C1 matrix defines the response of color projector 111. This matrix C1 is predefined and specific to the projector 111. It depends on the spectral response of each of the primary colors used by the projector 111.

Similarly, the color generated by the projector 112 when it receives input component J _or t can also be defined as follows:

• J Out

The column matrix Y. represents, in the XYZ color space, the

The color generated by the projector 112 and the matrix C2 defines the color response of the projector 112. This matrix C2 is predefined and specific to the projector 112. It depends on the spectral response of each of the primary colors used by the projector 112.

The XYZ color space being in addition an additive space, the resulting color displayed on the screen by the two projectors 111 and 112 is the sum of the colors produced by each of the projectors:

x _c

The column matrix then represents, in the XYZ color space,

the color generated by the display system according to the invention. When the

additional component J _or t is zero, we have and so

All these notations are used hereinafter to explain the operation of the transformation circuit 100.

FIG. 3 illustrates in more detail the functional diagram of the transformation circuit 100.

The circuit 100 comprises a block 1001 for transforming the first video data R _1n , V _1n , B _1n into color coordinates X _or t, Y _or t, Z _out in the space XYZ. This transformation is performed using the predefined matrix C1. These "first color coordinates" X _or t, Y _or t, Z _out thus obtained thus represent the color to be displayed using the two projectors in the XYZ color space independent of these projectors. A second block 1002 is then used to derive, from these first color coordinates X _or t, Y _or t, Z _or t, a value J _out which represents the additional color component of the second video data, or component of the fourth primary. This block 1002 is for example a predefined look-up table (or Look-Up Table) which is iteratively calculated as described later in the present description. In the context of the anti-copy defined in the preamble of the present description, it is advantageous for this additional component J _or t to be maximal in one of the metamer mixtures and to be zero in the other mixture so that the anti-copy message -copy be the most visible possible. Therefore, the value of the component J _or t delivered by the block 1002 is preferably the highest possible. In the context of the insertion of an anti-copy pattern in the image displayed by the display system 10, a transformation authorization circuit 1003 is provided at the output of the block 1002 to allow or not the transformation by the transformation circuit 100 according to a binary information present at the input of this circuit. This binary information is in this case a indication of the membership of the image pixel to be displayed in the anti-copy pattern to be inserted in the image to be displayed. If the pixel considered belongs to the anticopy pattern to be inserted, the circuit 1003 delivers the signal J _or t and, otherwise, it delivers a zero value. The signal delivered by the circuit 1003 is supplied to the projector 112. The signal delivered by the circuit 1003 is also processed by a block 1004. This block transforms the value J _out of the additional color component into second color coordinates X _or t2, Y _or t2 and Z _or t2 in the XYZ space. This transformation is performed using the predefined C2 matrix. A subtraction block 1005 is then provided for subtracting the second color coordinates X _out 2, Y _or t 2, Z _out 2 at the first coordinates Xout, Yout and Z ₀ Ut: the third colorimetric coordinates are then obtained.

Xouti, 'out1 and Z _O ut1, where Xout1 ⁼ Xout' Xout2, Yout1 ⁼ Yout 'Yout2 and Z _O ut1 ⁼ Z _O ut-Z _O ut2- The color associated with these third color coordinates is called the' remaining 'color. Finally, a block 1005 provides the other three missing components R _or t, V ₀ Ut, B ₀ Ut of the second video data from the third color coordinates X _or ti, Y _or ti, Z _or ti and the matrix C1 ^"1 which is the inverse of the predefined matrix C1. The transformation effected by the block 105 is therefore inverse to the transformation effected by the block 1001. These three components R ₀ Ut, V ₀ Ut, B ₀ Ut of the second video data are then supplied to the projector 111.

As previously mentioned, the block 1002 serves to determine a value J ₀ Ut of the additional color component of the second video data from the components of the first video data X _or t, Yout and Z ₀ Ut- This block is for example a table predefined conversion and this table is for example computed iteratively as follows: a) assign a maximum positive value to the component J _or t; if the values of the color components are between 0 and 255, the value 255 is assigned to J _or t; b) calculate the X _or ti, Y _or ti, Z _or ti colorimetric coordinates of the so-called "remaining" color as follows:

c) verifying that the third color coordinates X _or ti, Y _or ti, Z _or ti are actually displayable using the projector 111 alone; to this end, it should be verified that the product of the matrix C1 ^"1 by these third color coordinates X _or ti, Y _or ti, Z _or ti gives values R _or t, V _or t, B ₀ Ut which are positive and that the color defined by these third colorimetric coordinates or these values R _or t, V _or t, B _or t are located inside the color gamut of the projector 111, as long as this color is outside the color gamut of the projector. 111, decrement J _or t by a pre-defined quantity and start again in step b) above If the values of the color components are between 0 and 255, the value of J _or t is preferably decremented by 1 - Higher decrement values may be used without departing from the invention, whereby said value J _or t of the additional color component is determined to be maximum and so that the corresponding "remaining" color is actually displayed by the display device without using said additional color component. In a more computer language, the process can be written as follows:

For all possible combinations (X _O ut, Yout, Z _O ut),

take J _or t equal to a maximum value, for example 255;

- calculate the triplet (X _O ut2, Yout2, Z _O ut2) as

Out

- calculate the triplet (X _O uti, Youti, Z _O uti) as -Y out 2

as long as the triplet (X _O uti, _Y uti, Z _O uti) is outside the color gamut of the projector 111,

"Jout ~ <-Out '

- calculate the triplet (X _O ut2, Yout2, Z _O ut2) as

• J Out

- calculate the triplet (X _O uti, Youti, Z _O uti) as v _ Y outl out ^Λ ^Λ out2 outl Y - Y

^J outl ^J out2

End - associate, in the conversion table, the value J _out to the combination

(Xout, Yout, Z _O ut) considered.

Of course, the invention is not limited to the embodiments described above. In particular, those skilled in the art may use primary color components other than red, green or blue.

Moreover, the invention does not limit the embodiments shown in FIGS. 1 and 2, but concerns any display system capable of displaying at least four primary colors, for example DLP or LCD displays comprising more than 3 primaries for displaying a display. extended gamut.

Claims

A video image display method in which each pixel is represented by first video data (R _1n , V _1n , B _1n ) based on three first color components, using a display device ( 110; 111, 112) controllable with second video data (R _or t, V _or t,

Bout, Jout) based on said first three color components and an additional color component (J _or t), wherein said first video data (R _1n , V _1n , B _1n ) is transformed by at least one pixel said video image in seconds video data (R _or t, V _or t, B _or t, J ₀ Ut) where the additional color component (J _or t) is non-zero according to the following steps:

using a first transformation, transforming said first video data (R _1n , V _1n , B _1n ) of the at least one pixel into first colorimetric coordinates (X _or t, Yout, Z _or t) expressed in a linear color space;

a non-zero value of said additional color component (J _or t) of said second video data of the at least one pixel is determined according to said first colorimetric coordinates (X _or t,

• out, ^ -out), - using a second transformation, transforming said additional color component value (J _or t) into second colorimetric coordinates (X _or t2, Y _or t2, Z _or t2 ) in said linear color space;

by subtracting said second colorimetric coordinates (X _or t2, Y _O ut2, Z _or t2) with said first colorimetric coordinates (X _or t, Yout, Z ₀ Ut), third color coordinates (X _or ti, Y _or ti) are generated; ,

Z _O uti) in said linear color space, which correspond to a so-called "remaining"color;

using a third inverse transformation of the first transformation, transforming said third colorimetric coordinates (X _or ti, Y _or ti, Z _or ti) into values of said first three color components (R _or t, V _or t, B _or t) of said second data video of the at least one pixel, characterized in that said value of the additional color component (J _or t) is determined so as to be maximum and so that the corresponding "remaining" color is actually displayable by the display device without using said additional color component.

2. A video image display method according to claim 1 characterized in that said linear color space (CIE XYZ) is independent of any display device.

3. Video image display method according to claim 1 or 2, characterized in that the set of pixels for which the first video data (R _1n , V _1n , B _1n ) is converted into second data according to said steps. video (R _or t, V _or t, B _or t, Jout) forms an anti-copy pattern inserted in said video image.

A video image display system (10) comprising:

a transformation circuit (100) of first video data (R _1n , V _1n , B _1n ) of an image pixel to be displayed based on three first color components, in second video data (R _or t, V _or t, B _or t, Jout) based on said first three color components and an additional color component (J _or t),

a display device (110; 111, 112) of said image driven by said second video data, said transformation circuit (100) comprising:

a first block (1001) for transforming, by means of a first transformation, said first video data (R _1n , V _1n , B _1n ) into first colorimetric coordinates (X ₀ Ut, Yout, Z _out ) in a space of linear color,

a second block (1002) for determining, as a function of said first colorimetric coordinates (X _or t, Yout, Z _out ), a non-zero value of the additional color component (J _out ) of said second video data,

a third block (1004) for transforming by means of a second transformation said additional color component value (J ₀ Ut) into second colorimetric coordinates (X _or t2, Y _or t2, Z _out2 ) in said space linear color,

a fourth block (1005) for subtracting the second colorimetric coordinates (X _or t2, Y _or t2, Z _0Ut2 ) from said first colorimetric coordinates (X _or t, Y _or t, Z _out ) and generating third colorimetric coordinates (X _or ti, Y _or ti, Z _out i) in said linear color space, - a fifth block (1006) for transforming, using a third inverse transformation of the first transformation, said third colorimetric coordinates (X _or ti, Y _or t 1, Z _out i) in values of said first three color components (R _or t, V _or t, B _out ) of said second video data of the at least one pixel, characterized in that said value of the component of Additional color (J _or t) is determined to be maximum and so that the corresponding "remaining" color is actually displayable by the display device without using said additional color component.

5. A video image display system (10) according to claim 4 characterized in that said linear color space (CIE XYZ) is independent of any display device.

6. System according to any one of claims 4 to 5, further comprising a transformation authorization circuit (1003) interposed between the second block (1002) and the third block (1004), said transformation authorization circuit (1003) receiving as input the value of the additional color component (J _or t) determined by the second block (1002) and a binary information allowing or not the transformation of the first video data into second video data, which circuit (1003) delivers said value of the additional color component (J ₀ Ut) if said binary information authorizes the transformation and a null value otherwise.

The system of claim 6, wherein the binary information is transformational information when the current pixel belongs to an anti-copy pattern to be inserted into the video image.

The system of any one of claims 4 to 7, wherein the display device (110; 111,112) comprises a first projector (111) for displaying the first color components (R _or t, V _or t , B _out ) second video data and a second projector (112) for displaying the additional component of the second video data (J _or t) -