FR3053823A1 - TRANSPARENT SCREEN AND PROJECTOR FOR IMPROVED CONTRAST DISPLAY - Google Patents

Abstract

The invention relates to a transparent screen (10) for receiving a light signal (2) to form an image; the screen is remarkable in that it comprises: a display film (11) having a display face (11a) of the image and capable of reflecting or scattering the first wavelengths and transmitting second wavelengths; An opacifying film (12), disposed on the display film (11), on an opposite face (11b) to the display face (11a), and capable of passing from a transparent state to a substantially opaque state when exposed to an activation wavelength; the activation wavelength being part of the second wavelengths.

Description

(57) The invention relates to a transparent screen (10) intended to receive a light signal (2) to form an image; the screen is remarkable in that it includes:

a display film (11), having a display face (11 a) of the image and capable of reflecting or diffusing first wavelengths and of transmitting second wavelengths;

an opacifying film (12), disposed on the display film (11), on a face opposite (11b) to the display face (11a), and capable of passing from a transparent state to a substantially opaque state when exposed to an activation wavelength; the activation wavelength being part of the second wavelengths.

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TRANSPARENT SCREEN AND PROJECTOR FOR CONTRAST DISPLAY

IMPROVED

FIELD OF THE INVENTION

The present invention applies to the field of display screens. It relates in particular to a transparent display screen and an associated projector, as well as a display method.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Display display),

Transparent display screens find applications in a growing number of fields, including commercial, advertising (shop windows, terminals in communicating and interactive environments (game or educational screens) or even the field of “head-up” vision systems (screens instructions in cars, augmented reality glasses ...).

Common technologies of transparent screens for electronic display can be classified into three categories.

A first category corresponds to transmissive screens. These are essentially LCD-TFT screens (for "Liquid Crystal Display - Thin Film Transistor" according to English terminology). The principle is to selectively mask a light source, generally white, placed at a distance behind the screen. This light is then filtered both in intensity and in chromaticity, by a liquid crystal, polarizers and color filters. In this case, the active material is liquid crystal, controlled by a TFT matrix representing the different pixels.

The disadvantage of these screens is that they do not emit light and that visibility depends entirely on the background. Thus, they cannot display white if the background is not itself backlit in white. On the other hand, this technology has a relatively low transparency rate (around 10%).

A second category corresponds to emissive screens. This category mainly includes OLED (Organic Light-Emitting Diode) screens. The use of several principle materials consists of transparencies capable of emitting light (generally monochromatic) under certain conditions of excitation (electric current). This emissive material is itself integrated on a transparent substrate, and excited for example by a TFT matrix integrated into the screen. By combining 3 materials corresponding to the 3 primary colors, we can thus generate a wide palette of colors.

The disadvantage of these screens is that they can by nature only emit light, but cannot block it. Thus, they cannot display black.

Finally, a third category corresponds to reflective screens. These screens require a source image external to the screen, projected onto or through a transparent substrate serving as a screen. Depending on the optical configuration of the system and the type of reflective screen, the perceived image can be:

- virtual: this is the case with head-up vision systems (image formed behind a blade or a windshield), and augmented reality glasses,

- or real: this is the case with holographic screens (the image is formed on the screen itself).

In the case of virtual images, their visibility strongly depends on the position of the observer: these systems are generally reserved for an individual display (a single observer).

The downside of reflective screens in general is that they can reflect light, but cannot block it; therefore, they are unable to display black.

The common disadvantage of the different types of screens mentioned is that they do not allow the display of all the colors in addition to transparency: in the case of transmissive screens, it is not possible to display white ; in the case of emissive and reflective screens, it is not possible to display black. However, graphic designers working on the content to be displayed generally use a space with four dimensions: Red, Green, Blue, Alpha (this last dimension corresponding to the level of transparency). For each pixel, they therefore use all of the colors (including black and white) and decide the level of transparency with the background. Many image formats also support four-dimensional color space coding. These characteristics cannot however be fully exploited on a transparent screen of the state of the art, due to the limitations mentioned.

On the other hand, the readability of a transparent screen very strongly depends on the background, whether it is its color or its brightness. Thus, a transparent screen of the transmissive type will be very difficult to read if the background is not very bright or not chromatically neutral (ie, not "white"). Conversely, a transparent screen of the emissive or reflective type will be very difficult to read if the background is very bright.

OBJECT OF THE INVENTION

An object of the invention is therefore to propose a device which obviates all or part of the drawbacks of the prior art. An object of the invention is in particular a transparent screen with improved contrast and allowing the representation of a larger color space than the transparent screens of the prior art.

BRIEF DESCRIPTION OF THE INVENTION

The invention relates to a transparent screen intended to receive a light signal to form an image; the screen is remarkable in that it includes:

• a display film, having a display side of the image and capable of reflecting or diffusing first wavelengths and transmitting second wavelengths;

• an opacifying film, placed on the display film, on a face opposite to the display face, and capable of passing from a transparent state to a substantially opaque state when it is exposed to a wavelength d 'activation; the activation wavelength being part of the second wavelengths.

The characteristics of the transparent screen allow it to transpose the entire color space on a physical screen: the display film reflects or diffuses the first wavelengths of the visible spectrum allowing all the colors to be reconstructed, including the White ; the opacifying film makes it possible to filter the light coming from the background and to create an opaque zone, substantially black, when it receives the activation wavelength, which also makes it possible to display black on the picture. This last characteristic also makes it possible to improve the contrast of the image displayed on the display film by screening the surrounding light coming from the background, at the level of the objects to be displayed in the image, while retaining transparent areas not applicable.

According to advantageous characteristics of the invention, taken alone or in combination:

• the first wavelengths correspond to the three primary colors;

• the opacifying film comprises at least one photochromic material;

• the activation wavelength corresponds to a wavelength in the ultraviolet spectrum;

• the opacifying film comprises a bistable photochromic material, and is capable of passing from a substantially opaque state to a transparent state when it is exposed to a deactivation wavelength forming part of the second wavelengths;

• the deactivation wavelength is part of the visible spectrum;

• the opacifying film comprises at least one electrochromic material and comprises photosensitive components, capable of reacting to the activation wavelength, to control the electrochromic material and to make it pass from a transparent state to a substantially opaque state;

• the display film has reflective properties, the light signal being projected on the side of its display face;

• the display film has diffusive properties, the light signal being projected on the side of the face opposite to its display face;

• the display film and the opacifying film are placed on a transparent substrate or encapsulated between two transparent substrates.

The invention also relates to a projector intended to project a light signal to form an image on a transparent screen as above. The projector is configured to project the light signal comprising the first and second wavelengths, the activation wavelength being one of the second wavelengths.

According to advantageous characteristics of the invention, taken alone or in combination:

• the projector is configured to project the deactivation wavelength among the second wavelengths;

• the activation wavelength is at least projected on each pixel defining at least one object of the image;

• the activation wavelength is projected on peripheral pixels, adjacent to pixels defining at least one object of the image.

The invention finally relates to a method of displaying an image on a transparent screen comprising:

• The projection of a light signal on the transparent screen composed of a display film and an opacifying film;

• The reflection or diffusion of the first wavelengths of the light signal by the display film, to form the image on the transparent screen;

• The transmission of second wavelengths of the light signal, by the display film;

• The absorption of at least one activation wavelength forming part of the second wavelengths transmitted, by the opacifying film; said activation wavelength passing the opacifying film from a transparent state to a substantially opaque state.

According to advantageous characteristics of the invention, taken alone or in combination:

• the opacifying film is substantially opaque locally at the level of at least one object of the image or at the level of the external contours of at least one object of the image.

• the display process includes:

o stopping the projection of at least the first wavelengths of the light signal to make the image disappear;

o stopping the projection of the activation wavelength to change the opacifying film from a substantially opaque state to a transparent state;

• the display process includes:

o stopping the projection of at least the first wavelengths of the light signal to make the image disappear;

o stopping the projection of the activation wavelength;

o and substantially simultaneously, the projection of at least one deactivation wavelength forming part of the second wavelengths, on the transparent screen; said deactivation wavelength being capable of passing the opacifying film from a substantially opaque state to a transparent state;

• the activation wavelength is at least projected on each pixel defining an object of the image;

• the activation wavelength is projected onto peripheral pixels, adjacent to pixels defining an object of the image.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will emerge from the detailed description of the invention which will follow with reference to the appended figures in which:

Figure 1 shows a screen and a projector according to the invention;

Figures 2a, 2b, 2c show sectional views of transparent screens according to the invention;

Figures 3a and 3b show a first embodiment of a transparent screen and a projector, according to the invention;

FIG. 4 shows a second embodiment of a transparent screen and a projector, in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the descriptive part, the same references in the figures may be used for elements of the same nature. The figures are schematic representations which, for the sake of readability, are not to scale. In particular, the thicknesses of the films along the z axis are not to scale with respect to the lateral dimensions along the x and y axes.

The present invention relates to a transparent display screen 10, an associated projector 20 (FIG. 1), as well as a display method using the transparent screen 10 and the projector 20. In the following description, it will be made mention of an image 1, formed on the transparent screen 10 by the projection of a light signal 2. The image 1 corresponds to the area whose outline is defined by the projection of the light signal 2. It is composed of a matrix of pixels. Some pixels have a color and form one or more objects 3 that one wishes to view on image 1 (these pixels will be called "colored pixels" below); the other pixels have no color and constitute the transparent part 4, without object, of the image 1 (these pixels will hereinafter be called "transparent pixels").

2 shows a sectional view of the transparent screen 10 according to the invention. Intended to receive a light signal 2 to form an image 1, it comprises a display film 11, having a display face 11a of the image 1 and an opposite face 11b to the display face 11a. The light signal 2 is composed of a plurality of wavelengths. The to reflect or diffuse to transmit second display film 11 is suitable first wavelengths and wavelengths, the first and second wavelengths forming the plurality of wavelengths included in the light signal 2 The first wavelengths are intended to form the colored pixels (apart from the black pixels) defining the object (s) 3 of the image 1. When the light signal 2 is projected on the transparent screen 10, the first wavelengths are reflected or scattered by the display film 11, which makes it possible to form the image 1 on said film

11.

The display film 11, formed from polymers, has characteristics known from the state of the art under projection holographic. The display film 11 has a high light transmission coefficient (for example between 80 and 95%) for the entire visible spectrum, except the first wavelengths. This property gives it excellent transparency, while allowing good reflection of the first wavelengths intended to form the image. Advantageously, the first wavelengths correspond to the three primary colors, thus giving access to a large panel of colors for the colored pixels.

The display film 11 may have, for example, a thickness of the order of a few tens of microns.

from compounds common to films denomination "film

The transparent screen 10 also includes an opacifying film 12, placed on the display film 11, on the opposite face 11b to the display face 11a. The opacifying film 12 is capable of passing from a transparent state to an opacified state, defined in the following description as substantially opaque, when it is exposed to an activation wavelength.

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By opacified or substantially opaque is meant having an absorption coefficient of the visible spectrum at least greater than 50%.

A black or substantially black colored pixel can therefore be formed on the transparent screen 10 by the projection of the activation wavelength (to generate the opacification of the opacifying film 12), without the first wavelengths (for keep the display film transparent 11).

According to the invention, the activation wavelength is one of the second wavelengths: it is therefore included in the projected light signal 2 and is transmitted by the display film 11.

According to a first variant, the opacifying film 12 comprises at least one photochromic material. Photochromic materials are chemical substances, organic or inorganic, which can change color reversibly, in response to variations in intensity of particular wavelengths to which they are exposed. In general, photochromism results from a modification of the molecular configuration of the material under excitation which induces a modification of the absorption spectrum in the visible. Thus, exposed to the activation wavelength, the opacifying film 12 will absorb at least part of the wavelengths of the visible spectrum, thus becoming substantially opaque.

Most often, the activation wavelength for photochromic materials is part of the ultraviolet spectrum. It can possibly be included in the visible spectrum.

The photochromic material of the opacifying film 12 can advantageously combine different substances or molecules to obtain the most uniform possible absorption of the visible spectrum. This can make it more opaque and make it neutral from a colorimetric point of view.

The absorption rate of the visible spectrum of the opacifying film 12 being greater than or equal to 50%, the transparent screen 10 benefits from an improved contrast by a factor of two, compared to a configuration without opacifying film 12. In a further manner preferred, the absorption rate is greater than or equal to 80%, thus multiplying the contrast by a factor of five compared to a configuration without opacifying film 12.

There are several types of photochromic materials: some return to their initial state (transparent) as soon as they are no longer exposed to the activation wavelength; others (bistable photochromic materials), having a second stable state after excitation, require exposure to a deactivation wavelength to return to their initial state. According to the invention, the deactivation wavelength (at least one) is one of the second wavelengths: it is included in the projected light signal 2 and is transmitted by the display film 11. Usually, but without being limiting, the deactivation wavelength is included in the visible spectrum.

By way of example, the opacifying film 12 can comprise photochromic compounds of the diarylethene or spiropyran type.

According to a second variant, the opacifying film 12 can comprise at least one electrochromic material; in this case, it also comprises photosensitive components, capable of reacting to the activation wavelength: the photosensitive components have the role of controlling the electrochromic material, causing it to pass from a transparent state to a substantially opaque state.

Electrochromic materials can change color when subjected to electrical excitation. The photosensitive components exposed to the activation wavelength (s) will generate an electrical signal corresponding to said electrical excitation. The photosensitive components can also be configured, if necessary, a state of the invention, the to react to a deactivation wavelength: they then generate an electrical signal corresponding to an electrical excitation allowing the electrochromic material to pass from a substantially opaque to transparent state (initial state). According to the deactivation wavelength is one of the second wavelengths: it is therefore included in the projected light signal 2 and is transmitted by the display film 11.

The photosensitive components are preferably produced from semiconductors in thin layers: for example, they can be formed by photodiodes driving a transistor capable of generating the electrical control of the electrochromic material.

By way of example, for one or other of the two variants described, the opacifying film 12 may have a thickness of the order of a few hundred microns.

According to one or other of the variants mentioned above, the transparent screen 10 can have different shapes, in particular, it can be square, rectangular, circular, ellipsoidal, or other form of interest. In addition, the surface of the transparent screen 10 can be flat or curved, provided that the maximum amplitude of the curvature is maintained within the tolerance of depth of field of the projector 20. Very flexible as to its shape, the screen transparent 10 according to the invention can be used in multiple environments, for a large number of applications.

The transparent screen 10 according to the invention may comprise at least one transparent substrate 13 serving as a mechanical support or as a protective layer for one or both films 11 and 12. Advantageously, the opacifying film 12 is firstly laminated on the support substrate 13; the display film 11 is then laminated on the opacifying film 12. Advantageously, a protective layer 14 anti-scratch and anti-reflection is also deposited on the display face 11a of the display film 11 (FIG. 2b).

Alternatively, the display 11 and opacifying films 12 can be encapsulated between two transparent substrates 13 (FIG. 2c).

The invention also relates to a projector 20 intended to project the light signal 2 to form the image 1 on the transparent screen 10. As stated previously, the light signal 2 comprises the first and second wavelengths. The projector 20 is configured to project the activation wavelength (s) and, if necessary, the deactivation wavelength (s).

The projector 20 can be based on existing image projection technologies such as LCD video projection techniques (derived from liquid crystal screens), DLP ("Digital Light Processing"), laser, etc.

At least one light source capable of generating the activation wavelength is included in the projector 20. If necessary, at least one light source capable of generating the deactivation wavelength is also included in the projector 20. Each source is chosen to emit the wavelength in a substantially narrow spectrum centered on said wavelength, but not necessarily strictly monochromatic.

Due to the presence of additional light sources, the optical path in the projector 20 must be adapted so that the light beam from each source reaches the element making it possible to modulate and generate the light signal 2 to be projected.

Of course, the light sources intended to emit the first wavelengths will have to be chosen according to the properties of the display film 11 of the transparent screen 10, the first wavelengths having to be reflected or diffused by the film d display 11 to form image 1 on the transparent screen 10.

In certain cases, the activation wavelength could be projected on each colored pixel defining at least one object 3 of the image 1. This configuration makes it possible in particular to improve the contrast by screening the brightness of the rear -plan at the level of the object (s) 3 of image 1.

In other cases, for example for the display of a text, the activation wavelength may possibly be projected over the entire frame delimiting the text, so as to opacify the entire frame and thus to screen the background more widely.

In still other cases, the activation wavelength may be projected onto peripheral pixels, adjacent to pixels defining at least one object of the image. This configuration makes it possible in particular to form a substantially opaque contour around the object (s) 3 of the image and also improves the contrast of the display.

The operation of the transparent screen 10 and of the projector 20 according to the invention will be better understood with reference to the image display method 1 described below.

According to a first embodiment, the projector 20 is placed on the side of the display face 11a of the display film 11 of the transparent screen 10 and projects the light signal 2 directly on this display face 11a ( figure 3). The display film 11 has reflective properties, it reflects the first wavelengths of the light signal 2, which makes it possible to form the image 1 on the transparent screen 10; moreover, it transmits second wavelengths, different from the first and included in the light signal.

opaque, displayed

In the case of a transparent reflective screen of the state of the art, it is not possible to display black and the contrast of the image is highly dependent on the surrounding brightness.

The screen 10 according to the invention comprises an opacifying film 12, disposed on the opposite face 11b to the display face 11a of the display film 11. Thus, according to the display method according to the invention, at least an activation wavelength forming part of the second wavelengths transmitted by the display film 11 is absorbed by the opacifying film 12. The activation wavelength causes the opacifying film 12 to pass from a state transparent to a substantially opaque state.

Preferably, the opacifying film 12 passes in a substantially locally opaque state, at the level of at least one object 3 of the image 1. For this, the activation wavelength is projected at least on the colored pixels defining the or the object (s) 3 of the image 1. This makes it possible to filter the light coming from the background by creating a substantially black area, at the back of each object 3 Recall that a colored pixel is a pixel on which is projected at least a first wavelength (forming colors or white) or a pixel on which is projected the activation wavelength without the first wavelengths (forming black).

FIG. 3a presents a front view of a transparent screen 10 on which an image 1 is formed by the projection of the light signal 2 by the projector 20. FIG. 3b, in top view, shows a section of the screen 10 according to the plane P plotted in FIG. 3a. An opaque zone 120 is present at the rear of each object 3 of the image 1, due to the projection of the activation wavelength on the screen 10, at the level of each colored pixel. It is thus possible to transpose onto the transparent screen 10, the entire color space. The first wavelengths of the visible spectrum make it possible to reconstruct all the colors including white, and black can be displayed by means of the opaque zones 120 of the opacifying film 12. Furthermore, the contrast of the image 1 displayed on the film d the display 11 is greatly improved, by screening the surrounding light coming from the background, at the level of the objects 3 of image 1.

Depending on the applications, it may be advantageous to keep the non-applicable parts of image 1 and possibly the rest of the transparent screen 10 transparent if image 1 is smaller than that of screen 10: in this case , the activation wavelength is not projected on the transparent pixels, which makes it possible to preserve the transparent nature of the screen 10.

To make the image 1 disappear (prior to the projection of a new image, for example), the projection, at least, of the first wavelengths of the light signal 2 is stopped. The activation wavelength is also removed from the light signal 2. Thus, the opacifying film 12 is capable of returning to a transparent state either spontaneously or by the projection of at least one deactivation wavelength making part of the second wavelengths, on the transparent screen 10. The projection of the deactivation wavelength is substantially simultaneous with the stopping of the projection of the activation wavelength. By substantially simultaneous is meant operating in a short time interval, of the order of a second or less.

According to a second embodiment, the projector 20 is placed on the side of the opposite face 11b to the display face 11a of the display film 11 of the transparent screen 10 and projects the light signal 2 directly on the film clouding 12 (Figure 4). This configuration corresponds to a projection from the rear face of the screen 10. The opacifying film 12 is transparent, in its initial state, it therefore lets at least the first wavelengths pass. The display film 11 this time has diffusive properties. The display film 11 diffuses the first wavelengths of the light signal 2, which makes it possible to form the image 1 on the display face 11a of the display film 11 of the transparent screen 10.

According to this second embodiment of the display method, at least one activation wavelength, forming part of the second wavelengths, is projected by the projector 20 and absorbed by the opacifying film 12. The length activation wave changes the opacifying film 12 from a transparent state to a substantially opaque state.

Preferably, the opacifying film 12 passes into a substantially locally opaque state, at the level of the external contours of at least one object 3 of the image 1. For this, the activation wavelength is projected onto peripheral pixels, adjacent to pixels defining at least one object 3 of image 1. The peripheral pixels are transparent pixels located at the contour of the object or objects 3 of image 1. This configuration makes it possible to partially filter the light coming from the background and create an opaque peripheral zone 121, substantially black, at the level of each object 3 of image 1 (FIG. 4). The contrast of image 1 displayed on the display film 11 is thus improved, by emphasizing the contours of the objects 3 of image 1.

Depending on the applications, it may be advantageous to keep the non-applicable parts of image 1 and possibly the rest of the transparent screen 10 transparent if image 1 has a size smaller than that of the screen 10: the length d the activation wave is then not projected on the transparent pixels (not applicable), which makes it possible to preserve the transparent nature of the screen 10.

To make the image 1 disappear (prior to the projection of a new image, for example), the projection, at least, of the first wavelengths of the light signal 2 is stopped. The activation wavelength is also removed from the light signal 2. Thus, the opacifying film 12 is capable of returning to a transparent state either spontaneously or by the projection of at least one deactivation wavelength making part of the second wavelengths, on the transparent screen 10.

The transparent screen 10, the projector 20 and the display method according to the invention offer a solution for displaying on a transparent screen, improved graphic possibilities with improved contrast, and endowed with its ability to combine transparency and all of the color palette (including white and black). This solution is particularly advantageous for applications such as commercial or advertising display (transparent terminals or shop windows), informative display in vehicles, etc.

Of course, the invention is not limited to the embodiments and to the fields of application described and it is possible to make variant embodiments without departing from the scope of the invention as defined by the claims.

Claims (20)

1. Transparent screen (10) intended to receive a light signal (2) to form an image (1); the screen (10) being characterized in that it comprises: • a display film (11), having a display face (11a) of the image (1) and capable of reflecting or diffusing first wavelengths and transmitting second wavelengths; • an opacifying film (12), disposed on the display film (11), on a face opposite (11b) to the face (11a), and capable of passing from a state to a substantially opaque state when it is exposed to an activation wavelength; the activation wavelength being part of the second wavelengths. transparent display 2. Transparent screen (10) according to the preceding claim, wherein the first wavelengths correspond to the three primary colors. 3. Transparent screen (10) according to one of the preceding claims, in which the opacifying film (12) comprises at least one photochromic material. 4. Transparent screen (10) according to one of the preceding claims, in which the activation wavelength corresponds to a wavelength in the ultraviolet spectrum. 5. Transparent screen (10) according to one of the preceding claims, in which the opacifying film (12) comprises a bistable photochromic material, and is capable of passing from a substantially opaque state to a transparent state when it is exposed to a deactivation wavelength forming part of the second wavelengths. 6. Transparent screen (10) according to the preceding claim, wherein the deactivation wavelength is part of the visible spectrum. 7. Transparent screen (10) according to one of claims 1 and 2, in which the opacifying film (12) comprises at least one electrochromic material and comprises photosensitive components, capable of reacting to the activation wavelength, to control the electrochromic material and to pass it from a transparent state to a substantially opaque state. 8. Transparent screen (10) according to one of the preceding claims, in which the display film (11) has reflective properties, the light signal (2) being projected on the side of its display face (lia). 9. Transparent screen (10) according to one of claims 1 to 7, in which the display film (11) has diffusive properties, the light signal (2) being projected on the side of the opposite face (11b) to its display face (lia). 10. Transparent screen (10) according to one of the preceding claims, in which the display film (11) and the opacifying film (12) are arranged on a transparent substrate (13) or encapsulated between two transparent substrates (13) . 11. Projector (20) intended to project a light signal (2) to form an image (1) on a transparent screen (10) according to one of the preceding claims; the projector (20) being characterized in that it is configured to project the light signal (2) comprising the first and second wavelengths, the activation wavelength being one of the second wavelengths. 12. Projector (20) according to the preceding claim and one of claims 5 or 6, configured to project the deactivation wavelength among the second wavelengths. 13. Projector (20) according to one of the two preceding claims, in which the activation wavelength is at least projected on each pixel defining at least one object (3) of the image (1). 14. Projector (20) according to one of claims 11 to 12, in which the activation wavelength is projected onto peripheral pixels, adjacent to pixels defining at least one object (3) of the image ( 1). 15. Method for displaying an image (1) on a transparent screen (10) comprising: • The projection of a light signal (2) on the transparent screen (10) composed of a display film (11) and an opacifying film (12); • The reflection or scattering of the first wavelengths of the light signal (2) by the display film (11), to form the image (1) on the transparent screen (10); • The transmission of second wavelengths of the light signal (2), by the display film (11); • The absorption of at least one activation wavelength forming part of the second transmitted wavelengths, by the opacifying film (12); said activation wavelength passing the opacifying film (12) from a transparent state to a substantially opaque state. 16. Display method according to the preceding claim, in which the opacifying film (12) is substantially opaque locally at the level of at least one object (3) of the image (1) or at the level of the external contours of at least one object (3) of the image (1). 17. Display method according to one of the two preceding claims, comprising: • stopping the projection of at least the first wavelengths of the light signal (2) to make the image (1) disappear; • Stopping the projection of the activation wavelength to change the opacifying film (12) from a substantially opaque state to a transparent state. 18. Display method according to one of claims 15 or 16, including • • The judgment of the projection of minus the first lengths wave of signal luminous (2) for make disappear The picture (U i; • The judgment of the projection of the wave length activation; • And substantially simultaneously, the projection of at least one deactivation wavelength forming part of the second wavelengths, on the transparent screen (10); said deactivation wavelength being capable of passing the opacifying film from a substantially opaque state to a transparent state. 19. Display method according to one of claims 15 to 18, in which the activation wavelength is at least projected on each pixel defining an object (3) of the image (D · 20. Display method according to one of claims 15 to 18, in which the activation wavelength is projected onto peripheral pixels, adjacent to pixels defining an object (3) of the image (1) .