Device for displaying images comprising two modulation stages

Abstract

Device comprising: a rear panel comprising a network of backlighting elements, a front panel comprising a network of optical valves which are each capable of modulating the brightness of a single primary colour. By the modulation of chrominance which is added to the modulation of luminance for the backlighting elements of the rear panel, the device according to the invention makes it possible to display the images with even more contrast and better quality. A specific control mode makes it possible to avoid the colour “interferences”.

Claims

1. A method of displaying at least one image, the method comprising: modulating luminance and chrominance of a network of backlighting elements associated with a rear panel of a display, wherein the modulating of the luminance and chrominance is a function of display data corresponding to pixels of an image, the luminance and chrominance modulated backlighting elements each generating primary colors; optically coupling of each of the backlighting elements of the rear panel to a group of a plurality of elementary sets of optical valves associated with a front panel, wherein each of the elementary sets of optical valves includes one optical valve for each of the primary colors, wherein each of the elementary sets of optical valves displays a pixel of the image; and modulating, using each of the optical valves of the group, a brightness associated with each of the generated primary colors received from each of the backlighting elements; wherein modulating the brightness of each optical valve of the group is a function of display datum associated with a pixel of the image corresponding to an elementary set of the group to which the optical valve belongs, and wherein the brightness of each of the optical valves of the group is modulated as a function of display datum associated with a pixel of the image corresponding to other elementary sets within the group.

2. The method of claim 1, wherein the brightness of each of the optical valves of the group is further modulated as a function of display datum associated with a pixel of the image corresponding to at least one other elementary set than the elementary set of the group to which the optical valve belongs.

3. The method of claim 1, wherein each backlighting element comprises one emitter for each of the generated primary colors.

4. The method of claim 1, wherein a brightness modulation factor $[\hspace{1em}\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}]$ of each of the optical valves of the group conforms to $\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]=\underset{3\times N}{\mathrm{xyz}}.Math.\left({\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{LED}}^T\left[\begin{array}{c}{R}_{\mathrm{LED}}\\ G_{\mathrm{LED}}\\ B_{\mathrm{LED}}\end{array}\right].Math.*{\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{Mod}}^T\left[\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}\right]\right),$ where $\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right],$ represents a color vector of the display datum associated with a pixel of the image, where $[\hspace{1em}\begin{array}{c}{R}_{\mathrm{LED}}\\ G_{\mathrm{LED}}\\ B_{\mathrm{LED}}\end{array}]$ represents luminance and chrominance modulation factors of the backlighting element optically coupled to a group of a plurality of elementary sets of optical valves associated with the pixel, where $\underset{3\times N}{\mathrm{xyz}}.Math.$ represents a matrix of colorimetric functions of reference primaries of a color space in which the color vector is expressed, where ${\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{LED}}$ represents an emission spectra of the backlighting element when all the modulation factors of this element are zero, except one, where ${\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{MOD}}$ represents a transmission spectra of the optical valve for each of the primary colors of the elementary set of optical valves.

5. The method of claim 1, wherein each backlighting element comprises one emitter generating one primary color or a combination of primary colors.

6. A display device comprising: a rear panel comprising a network of backlighting elements that each have modulable luminance and chrominance, wherein modulating of the luminance and chrominance is a function of display data corresponding to pixels of an image, wherein the luminance and chrominance modulated backlighting elements each generate primary colors; a front panel comprising a group of a plurality of elementary sets of optical valves, wherein each of the elementary sets of optical valves includes one optical valve for each of the primary colors, each of the elementary sets of optical valves displaying a pixel of the image, each of the optical valves of the group modulating a brightness associated with each of the generated primary colors received from each of the backlighting elements; and wherein each of the backlighting elements of the rear panel is optically coupled to a group of a plurality of elementary sets of optical valves associated with the front panel; wherein each optical valve of the group modulates the brightness as a function of display datum associated with a pixel of the image corresponding the elementary set of the group to which the optical valve belongs; and wherein each of the optical valves of the group modulates the brightness as a function of display datum associated with a pixel of the image corresponding to other elementary sets within the group.

7. The display device according to claim 6, wherein each optical valve comprises a liquid-crystal cell for modulating the brightness, and a colored optical filter capable of transmitting the generated primary color received from each of the backlighting elements optically coupled to the group to which the optical valve belongs, wherein each colored optical filter is associated with a transmission spectrum.

8. The display device according to claim 7, wherein each backlighting element comprises one emitter for each of the generated primary colors, wherein each emitter is associated with an emission spectrum; wherein each optical valve is associated with one emitter for the primary color; and wherein the transmission spectrum of the colored filter of the optical valve covers the emission spectrum of the emitter of a generated primary color and, at least partially, the emission spectrum of at least one other emitter of the same backlighting element for at least one other generated primary color.

9. The display device according to claim 8, wherein the emitters are light-emitting diodes.

10. The display device according to claim 7, wherein each backlighting element comprises one emitter generating one primary color or a combination of primary colors; wherein the emitter is associated with an emission spectrum; and wherein the transmission spectrum of the colored filter of the optical valve covers the emission spectrum of the emitter generating one primary color or a combination of primary colors.

11. The display device according to claim 10, wherein the emitter is a light-emitting diode.

12. The display device according to claim 6, wherein the backlighting elements have modulable chrominance at least in a whole of a range of colors that is delimited by the generated primary colors.

13. The display device according to claim 6, further comprising a light diffuser panel comprising a rear diffusion layer, a front diffusion layer, and a transparent thick layer inserted between the rear diffusion layer and the front diffusion layer, wherein the light diffuser panel optically couples the backlighting elements to the group of the plurality of elementary sets of optical valves.

Description

(1) The invention will be understood more clearly from a reading of the following description given by way of non-limiting example, and with reference to the accompanying figures in which:

(2) FIG. 1 gives the emission spectrum of the various diodes of a backlighting element of the display device according to the embodiment of the invention illustrated in FIG. 3;

(3) FIG. 2 gives the transmission spectrum of the coloured filters of the various optical valves of an elementary display set of the display device according to the embodiment illustrated in FIG. 3;

(4) FIG. 3 illustrates an embodiment of the display device according to the invention.

(5) Referring to FIG. 3, a device for the display of images having three primary colours P.sub.R, P.sub.G, P.sub.B according to an embodiment of the invention will now be described. This device comprises: a rear panel 1 comprising a network of backlighting elements which have modulatable luminance and chrominance; each backlighting element comprises three light-emitting diodes D.sub.R, D.sub.G, D.sub.B (D.sub.B not illustrated in FIG. 3), here a diode for each primary colour P.sub.R, P.sub.G, P.sub.B, as described, for example, in the document EP1717633; referring to FIG. 1, the emission spectra of these light-emitting diodes D.sub.R, D.sub.G, D.sub.B as a function of the wavelength are represented by

(6) ${\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{LED}},$
where N is the number of wavelength sampling steps of these spectra; R.sub.LED, G.sub.LED, B.sub.LED refer to the respective modulation desired values of the diodes D.sub.R, D.sub.G, D.sub.B which make it possible to obtain a modulation both of the luminance and of the chrominance of the backlighting element; a front panel 2 comprising a network of optical valves (not illustrated in FIG. 1); each optical valve comprises a liquid-crystal cell making it possible to modulate the brightness at the output of this valve and a coloured optical filter positioned at the input of this valve; these optical valves are distributed in the form of elementary sets of adjacent optical valves, such that each elementary display set comprises an optical valve V.sub.R, V.sub.G, V.sub.B for each primary colour P.sub.R, P.sub.G, P.sub.B; referring to FIG. 2, the transmission spectra of the respective coloured filters F.sub.R, F.sub.G, F.sub.B of each valve V.sub.R, V.sub.G, V.sub.B of the same elementary display set are represented by

(7) ${\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{MOD}},$
where N is the number of wavelength sampling steps of these spectra; R.sub.Mod, G.sub.Mod, B.sub.Mod refer to the respective modulation desired values of the valves V.sub.R, V.sub.G, V.sub.B of the same elementary display set, which make it possible to obtain a modulation of only the brightness of the colour filtered respectively by the filters F.sub.R, F.sub.G, F.sub.B; means 3 for the optical coupling of each backlighting element of the rear panel 1 to a backlit group of the front panel 2 comprising a plurality of elementary sets of optical valves; such coupling means are described, for example, in the document WO03/077013 where use is made of cylindrical guides with reflecting walls forming a “honeycomb” structure between the rear panel 1 and the front panel 2; use is made here of conical light guides 31, as described for a different application in the document U.S. Pat. No. 5,839,823.

(8) The optical coupling means likewise comprise here a light diffuser panel 4 comprising a rear diffusion layer 41, a front diffusion layer 42 and a transparent thick layer 43, generally a glass plate, inserted between the diffusion layers 41 and 42. The rear diffusion layer 41 serves for forming a secondary light source at the end of each light guide 31. By virtue of the front diffusion layer 42, the emitting surface seen by an observer of the images displayed by the device will advantageously appear very near to the front panel of optical valves, this being beneficial to the display quality. Finally, by virtue of the inserted transparent thick layer 43, the mix of the radiation emitted by the various diodes of the same backlighting element is improved, thereby improving the backlighting homogeneity.

(9) The various components of the display device which have just been described are manufactured and assembled in a way known per se. One advantage of this display device is that each backlighting element can have its chrominance modulated at least in the whole of the range of colours which is delimited by the emission colours of the diodes of this element.

(10) As can be seen by comparing FIGS. 1 and 2, the transmission spectrum of each of the coloured optical filters covers the emission spectra of at least two light-emitting diodes associated with different primary colours. It is these covers which, in particular, are responsible for the colour interference problems which the display method according to the invention solves.

(11) A method for the display of images with the aid of the image display device which has just been described, according to an embodiment of the invention, will now be described.

(12) Each pixel of an image to be displayed corresponds to an elementary display set of the front panel which, as described above, groups together adjacent optical valves V.sub.R, V.sub.G, V.sub.B of different primary colours which can be modulated respectively according to the desired values R.sub.Mod, G.sub.Mod, B.sub.Mod.

(13) Conventionally, each pixel is coded in the form of a colour vector

(14) 0$\hspace{1em}\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]$
in a given colour space XYZ; the colorimetric spectral functions of the reference primaries of this space are grouped together in the form of a matrix

(15) $\underset{3\times N}{\mathrm{xyz}.Math.},$
where N is the number of wavelength sampling steps of these functions.

(16) If the display data are available only in a conventional format, called “RGB”, these data can conventionally be converted into a format called “XYZ” independent of any device, according to the conventional formula:

(17) $\left[\begin{array}{c}{X}_C\\ Y_C\\ Z_C\end{array}\right]=M_{\mathrm{XYZ}}^{-1}\left[\begin{array}{c}{R}_C\\ G_C\\ B_C\end{array}\right],\mathrm{where}$$M_{\mathrm{XYZ}}=\left\{\begin{array}{ccc}3.240479& -1.5377150& -0.498535\\ -0.969256& 1.875992& 0.041556\\ 0.055648& -0.204043& 1.057311\end{array}\right\}$$\mathrm{and}\mathrm{where}\mathrm{white}\mathrm{is}\mathrm{the}$
and where white is the
conventional illuminant D65.

(18) According to the invention, in order to display each image, by applying the modulation desired values R.sub.LED, G.sub.LED, B.sub.LED respectively to the diodes D.sub.R, D.sub.G, D.sub.B of each backlighting element of the rear panel, both the luminance and the chrominance of each backlighting element of the rear panel are modulated as a function of the colour vectors

(19) $\hspace{1em}\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]$
of the pixels of this image which correspond to the elementary display sets belonging to the same backlit group of the front panel which is coupled optically to this backlighting element. In order to obtain the modulation desired values R.sub.LED, G.sub.LED, B.sub.LED which determine the colour emitted by each backlighting element, the following operations are typically carried out: low-pass spatial filtration of the image to be displayed; resampling of the image at a resolution corresponding to the dimensions of the backlighting elements; optionally, spatial deconvolution in order to limit the “halo” effects attributable to the diodes.

(20) Simultaneously, by applying the respective modulation desired values R.sub.Mod, G.sub.Mod, B.sub.Mod to the valves V.sub.R, V.sub.G, V.sub.B of each elementary display set of this same backlit group, only the brightness is modulated of the colour then emitted by this backlighting element and filtered by the filters F.sub.R, F.sub.G, F.sub.B of the valves V.sub.R, V.sub.G, V.sub.B of this elementary display set.

(21) As described in more detail below, the display of the images is ensured such that, for each elementary display set corresponding to a pixel, the image datum of which is expressed by the colour vector

(22) $\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right],$
the brightness modulation factor

(23) $\left[\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}\right]\hspace{1em}$
of each optical valve (V.sub.R, V.sub.G, V.sub.B) of this elementary display set conforms to the equation:

(24) $\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]=\underset{3\times N}{\mathrm{xyz}}.Math.\left({\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{LED}}^T\left[\begin{array}{c}{R}_{\mathrm{LED}}\\ G_{\mathrm{LED}}\\ B_{\mathrm{LED}}\end{array}\right].Math.*{\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{Mod}}^T\left[\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}\right]\right).$

(25) To solve this equation and determine the values of R.sub.Mod, G.sub.Mod, B.sub.Mod, the following procedure, for example with successive iterations, is carried out: 1) an initial value

(26) $\left[\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}\right]:=\left[\begin{array}{c}{R}_{\mathrm{LED}}\\ G_{\mathrm{LED}}\\ B_{\mathrm{LED}}\end{array}\right]$
is adopted; 2)

(27) $\left[\begin{array}{c}{X}^{\prime }\\ Y^{\prime }\\ Z^{\prime }\end{array}\right]=\underset{3\times N}{\mathrm{xyz}}.Math.\left({\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{LED}}^T\left[\begin{array}{c}{R}_{\mathrm{LED}}\\ G_{\mathrm{LED}}\\ B_{\mathrm{LED}}\end{array}\right].Math.*{\underset{3\times N}{\mathrm{rgb}}}_{\mathrm{Mod}}^T\left[\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}\right]\right)$
is then calculated, 3) the deviation

(28) $\Delta =\mathrm{Abs}\left(\left[\begin{array}{c}{X}^{\prime }\\ Y^{\prime }\\ Z^{\prime }\end{array}\right]-\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]\right)$
is deduced from this, and there is a return to step 1) above with a new value

(29) 0$\left[\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}\right]:=\left[\begin{array}{c}{R}_{\mathrm{Mod}}\\ G_{\mathrm{Mod}}\\ B_{\mathrm{Mod}}\end{array}\right].Math.*\left(\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right].Math./\left[\begin{array}{c}{X}^{\prime }\\ Y^{\prime }\\ Z^{\prime }\end{array}\right]\right).$

(30) Operations 1) to 3) are repeated until the deviation Δ is below a predetermined threshold.

(31) By carrying out the display of the images in this way by modulating both the luminance, as in the prior art, and also the chrominance of the backlighting elements, the network of backlighting elements of the rear panel 1 is utilized much more profitably, and the contrast and, above all, quality of display of the images are also improved.

(32) The display quality is improved because, in particular, the modulation of each valve not only takes into account the primary colour, the brightness of which this valve is capable of modulating, but also the other primary colours, thus making it possible to avoid the colour interferences.

(33) The present invention has been described with reference to a rear backlighting panel based on light-emitting diodes; it is clear to a person skilled in the art that it may apply to other types of emitters, without departing from the scope of the following claims.

(34) The present invention has been described with reference to a front panel of optical valves based on liquid crystals; it is clear to a person skilled in the art that it may apply to other types of optical valves, without departing from the scope of the following claims.