FR2995751A1 - Self-calibrating stereoscopic screen calibrating method for use in auto-stereoscopy field, involves adjusting screens such that moment of transitions associated with reference screen and screens to be calibrated coincide - Google Patents

Abstract

The method involves displaying a stereoscopic calibration image on a reference auto-stereoscopic screen (1a) and on auto-stereoscopic screens to be calibrated (1b), and acquiring a video sequence by a mobile video acquisition unit (2). The video sequence is acquired during a displacement of the video acquisition unit with regard to the auto-stereoscopic screens. The screens are adjusted such that moment of transition associated with the reference auto-stereoscopic screen coincides with moment of transition associated with auto-stereoscopic screens to be calibrated. Independent claims are also included for the following: (1) a system for calibrating a self-calibrating stereoscopic screen (2) a computer program product comprising instructions for performing a method for calibrating a self-calibrating stereoscopic screen (3) a computer readable storage unit with instructions for performing the method for calibrating a self-calibrating stereoscopic screen.

Description

GENERAL TECHNICAL FIELD The present invention relates to the field of auto-stereoscopy. More specifically, it relates to a method for calibrating auto-stereoscopic screens juxtaposed. STATE OF THE ART Auto-stereoscopy is a type of stereoscopic image representation (that is to say in relief) requiring to restore the three-dimensional effect no complementary device such as glasses. The relief impression is obtained in the auto-stereoscopic screens by means of a network of microlenses (lenticular array) or filters (parallax barrier) placed on its surface, the displayed image being composed of intertwined images each representing a point from a different angle. Provided that the observer is correctly placed in front of the screen, the network makes it possible to address to each of his eyes a different image, his brain then reconstituting the relief. Lateral movements can position the observer outside a "viewing area" (ie each eye does not capture the image it is supposed to capture) and the 3D-relief effect is no longer perceived. , the displayed image becomes blurry and uncomfortable to watch. The new generation of auto-stereoscopic screens, called "multi-view", makes it possible to reduce this problem. These screens, instead of displaying only two views (one for the left eye and one for the right eye), display more (4, 8 and 9 are common values). Figure 1a thus illustrates an 8-view display. Each of these views corresponds to the scene viewed from a different angle. Thus, by moving laterally, the observer feels like he is turning around the scene, without losing the 3D effect. Referring to Figure 1, if the observer moves 6.5 centimeters to the right, the view he saw with his right eye is then seen by his left eye, and a new view is addressed to his right eye. . The viewing area therefore increases according to the number of views viewable by the 3D screen: for a screen with N views, an observer placed at the optimal viewing distance is correctly positioned N-1 times on N. The increase in the number For these reasons, the number of views greatly increases the observer's positioning comfort in front of the screen. In addition, several people can simultaneously enjoy the 3D effect.

The disadvantage, however, is that it is very difficult to place multiple auto-stereoscopic multi-view screens side-by-side or on top of each other, so that users can see the displayed content correctly. relief. This is because the screens render different views in the space according to the viewing angle.

The observation of these screens juxtaposed would be particularly unpleasant for a person. It is for this reason that we do not see for the moment of matrices of auto-stereoscopic screens. There are tracking devices that solve this problem (by detecting the position of an observer and adapting the image of one or more of the screens accordingly in real time), but they are still limited. to one or two users. It is therefore impossible to make them work with an assembly of 20 or 50 people for example. It would therefore be desirable to have a solution allowing a large number of people to enjoy 3D visualization without glasses on a display wall composed of several screens juxtaposed (horizontally, vertically or combination of both).

PRESENTATION OF THE INVENTION The present invention thus relates, according to a first aspect, to a method of calibrating at least one auto-stereoscopic screen to be calibrated with respect to an auto-stereoscopic reference screen, each auto-stereoscopic screen being a screen. multi-view device capable of displaying a stereoscopic image composed of N interlaced images where each image corresponds to a view, the method being characterized in that it comprises steps of: (a) Displaying on said auto-stereoscopic screens of an image stereoscopic calibration composed of N interlaced elementary images; (b) Acquiring a video sequence by mobile video acquisition means positioned so as to allow simultaneous observation of said auto-stereoscopic screens, said video sequence being acquired during a movement of the video acquisition means with respect to said screens auto-stereoscopic; (c) Analysis by data processing means of said acquired video sequence so as to detect for each auto-stereoscopic screen a transition time of a first elementary image in, nE litm corresponding to a first view, to a second image elementary / (n + 1) dnodu / oW corresponding to the following view; (d) If the transition time associated with the auto-stereoscopic reference screen is different from the transition time associated with the auto-stereoscopic screen to be calibrated, adjusting the auto-stereoscopic screen to be calibrated so that the transition time associated with the auto-stereoscopic reference screen coincides with the transition time associated with the auto-stereoscopic screen to be calibrated. The present invention aims to easily calibrate and at one time a wall of auto-stereoscopic screens so that a large number of people can simultaneously appreciate the visualization.

In addition, this calibration can be performed completely automatically. According to other advantageous and non-limiting characteristics: the method furthermore comprises, in case of adjustment of the auto-stereoscopic screen to be calibrated, the repetition of steps (a) to (c) as long as the moment of transition associated with the auto-stereoscopic reference screen does not coincide with the transition time associated with the auto-stereoscopic screen to be calibrated. This makes it easy to check if the calibration is satisfactory. the displacement of the mobile video acquisition means is a translation on a rail disposed along an axis parallel to the plane formed by the auto-stereoscopic reference screen. The use of a rail simplifies the movement of the camera. said translation axis is in the focal plane of the auto-stereoscopic reference screen. This is the plane in which the observation conditions of the screens are the best. each reference image Ik is a uniform color image. Such colors are easily identifiable by image analysis software, which facilitates the automation of the process. the adjustment of the auto-stereoscopic screen to be calibrated consists in its reversal and / or in the modification of its orientation and / or in the rotation of the views. Such adjustments can be easily done by an operator, or even automatically, and can correct any calibration problems encountered. the auto-stereoscopic screen to be calibrated is equipped with orientation means able to be controlled by the data processing means, the adjustment of the auto-stereoscopic screen to be calibrated consisting in the modification of its orientation as a function of the difference found in step (d) between the transition time associated with the auto-stereoscopic reference screen and the transition time associated with the auto-stereoscopic screen to be calibrated. These features pave the way for the most complete and fastest automation of the process. said transition is that of the reference image IN corresponding to the last view at the reference image / 1 corresponding to the first view. It is the pair of "pseudo-scopie", corresponding to the transition most easily identifiable visually. at least a first and a second auto-stereoscopic screen are to be calibrated with respect to the auto-stereoscopic reference screen, the first and second auto-stereoscopic screens being juxtaposed, the method comprising the calibration of the first auto-stereoscopic screen to calibrating with respect to the auto-stereoscopic reference screen, then calibrating the second auto-stereoscopic screen to be calibrated with respect to the first auto-stereoscopic screen to be calibrated. Thus, the method can close calibrate any surface of auto-stereoscopic screens, whatever the size. According to a second aspect, the invention relates to a system for calibrating at least one auto-stereoscopic screen to be calibrated with respect to an auto-stereoscopic reference screen, each auto-stereoscopic screen being a multi-view screen capable of displaying a stereoscopic image composed of N interlaced images where each image corresponds to a view, the system being characterized in that it comprises mobile video acquisition means positioned so as to allow the simultaneous observation of said auto-stereoscopic screens and means of data processing ; the auto-stereoscopic screens, the video acquisition means and the data processing means being configured for the implementation of the method according to the first aspect of the invention.

This system installs easily in front of a wall of screens and allows as explained their calibration easily and quickly. It can also be reinstalled if additional screens are later added.

According to a third and a fourth aspect, the invention relates respectively to a computer program product comprising code instructions for executing, when this program product is executed by data processing means, a method for calibrating the program. at least one auto-stereoscopic screen to be calibrated with respect to an auto-stereoscopic reference screen according to the first aspect of the invention; and computer-readable storage means on which a computer program product includes code instructions for executing a method of calibrating at least one auto-stereoscopic screen to be calibrated with respect to an auto display. stereoscopic reference according to the first aspect of the invention. PRESENTATION OF THE FIGURES Other features and advantages of the present invention will appear on reading the description which follows of a preferred embodiment. This description will be given with reference to the accompanying drawings in which: - Figure I has been described above is a diagram illustrating the known principle of operation of a multi-view auto-stereoscopic screen; FIG. 1b is a diagram illustrating an example of interleaving of 8 images in a stereoscopic 8-frame image; FIG. 2 represents a first embodiment of a system for implementing a method according to the invention; FIG. 3 represents a second embodiment of a system for implementing a method according to the invention.

The present invention relates to the calibration of multi-view auto-stereoscopic screens, that is to say screens capable of displaying a stereoscopic image composed of a plurality of interlaced images where 5 each image corresponds to a view. Figure 1b shows a detail of an example of interlacing of 8 images in such a stereoscopic image: each block is a pixel of the image composed of three sub-pixels (one red, one green and one blue). The number on each sub-pixel indicates which of the 8 images the sub-pixel 10 belongs to. As you can see, the images are completely nested inside each other. Note that the three sub-pixels reconstructing the same pixel of one of the 8 images are arranged diagonally in three successive rows. The auto-stereoscopic means integrated in the screen make it possible to separate the light rays corresponding to each of the images and to display them at different angles as explained above. Each auto-stereoscopic screen here is advantageously a lenticular array screen or a parallax barrier screen. These are the two main auto-stereoscopic screen technologies suitable for images such as that shown in Figure 1b. It should be noted that the term "image" should also be understood as a moving picture, ie a movie. Auto-stereoscopic screens are indeed able as any screen to display a sequence of images chaining at high speed. With reference to FIGS. 2 and 3, at least one screen 1b, 1c is calibrated with respect to a reference screen 1a. For the convenience of the users, it is preferable that the different auto-stereoscopic screens 1a, 1b, 1c have the same number of views and the same focal length (or "flat color distance", that is, the minimum focusing distance of the images in the image focal plane of the screen, the distance at which a display homogeneity is observed, it is generally determined during the construction of the screen). In the remainder of the present description, it will be considered that the screens 1 a, 1 b, 1 c are N-view screens, in other words screens capable of displaying a stereoscopic image composed of N interlaced images. 2, 4, 8, 9 views are common values. 2 is the minimum value (this corresponds to a view for the left eye and a view for the right eye) and 8 is the value used for the examples of Figures 1a and 1b. The auto-stereoscopic screens 1a, 1b, 1c are juxtaposed as can be seen in FIGS. 2 and 3. In other words, they are adjacent two by two, both horizontally and vertically or in combination. We can thus calibrate a wall of screens. It should be noted that two adjacent screens are possibly joined, so that the composite image that will be subsequently displayed on the plurality of screens is as uniform as possible, but it is quite possible to place a space between two screens. Furthermore, it should be noted that the invention is not limited to the calibration of walls "plan" screens, and that they can quite be arranged on a curved wall, so as to produce a cockpit effect. Whatever the geometry of the screen wall, the auto-stereoscopic reference screen 1a is a screen chosen arbitrarily, relative to which the other screens 1b, 1c will be calibrated, either all at once, or step by step as we will see. For convenience one can choose a central screen as reference screen 1a. Stereoscopic Calibration Image The calibration method according to the invention uses mobile video acquisition means 2 (in particular a digital camera) positioned so as to allow the simultaneous observation of said auto-stereoscopic screens 1a, 1b, 1c . In a first step is displayed on said auto-stereoscopic screens 1a, 1b, 1c of a stereoscopic calibration image composed of N elementary images ik, kE111, N11 interleaved. By "elementary" images we mean simple and easily differentiable images (whether to the naked eye by an operator or optically by image processing software). Indeed, the images composing an ordinary stereoscopic image are generally very similar. (since they correspond to the same scene viewed from a slightly different angle). For example, each reference image 1k is a uniform color image, the set of colors being defined via a pattern (so that each color is as distinct as possible from the other colors). Thus, it is possible to instantly know at any moment what is the view contemplated. Alternatively, patterns, grayscale, etc. can be used.

Transition of view A video sequence is then acquired by the mobile video acquisition means 2 mentioned above. The video sequence is acquired during a displacement of the video acquisition means 2 with respect to said auto-stereoscopic screens 1a, 1b, 1c. The purpose of this displacement is to detect if possible on each of the auto-stereoscopic screens 1a, 1b, 1c a moment called "view transition". Indeed, unlike a human, who sees two views simultaneously because of his two eyes, a camera has only one lens, and therefore sees only one view among the N at any time (provided that the camera is substantially at focal length of the screen, otherwise two views may sometimes partially interfere), depending on its position (see Figure 1a). The displacement of the camera 2 makes at least the passage from one first view to another is observed. It is the moment of transition of a first elementary image in, nE litm corresponding to a first view, to a second elementary image i (n + 1) Unodulo31 corresponding to the following view. It should be noted that, for example, if the views are numbered according to a rotation in the trigonometric direction around the scene (in other words, the view of a 1k image is farther to the left than the view of the image. an image 4 + 1) the transition is observed by moving the camera 2 from the left to the right in front of the screens 1a, 1b, 1c. However, this direction of numbering is purely arbitrary: if we move the camera to the contrary of the right to the left, it is enough to number the views in the other direction to observe the expected transition.

This transition is noted by the color change of the display. The transition from any one image to the next is sufficient to implement the present method, but advantageously we aim a transition from the reference image IN corresponding to the last view to the reference image / 1 corresponding to the first view. This transition, called a "pseudo-scopie" transition, is both the easiest to identify and the one whose impact is greatest in the event of poor calibration. Indeed, it is the most uncomfortable position because an observer sees the scene in inverted relief. The displacement of the camera 2 can in particular be operated so that a complete period of the views is observed, that is to say the sequence of the views / 1.4, (in other words a complete loop comprising N transitions). The displacement of the mobile video acquisition means 2 is advantageously a translation on a rail 3 disposed along an axis 20 parallel to the plane formed by the auto-stereoscopic reference screen 1a, this axis being preferably in the focal plane of the reference screen 1 a. The acquired video sequence is then processed by data processing means 4, in particular those of a computer equipment 25 connected to the digital camera 2, for example via an HDMI interface. An image analysis software can identify in the sequence said transition time associated with each screen 1a, 1b, 1c. For this purpose, the data processing means 4 (for example via a file stored on data storage means connected to the data processing means 4) are indicated with a table of correspondence of the views and associated colors associated in the data processing means 4. stereoscopic calibration image.

Thus, the expected order of the colors observed during the displacement is known. If the transition instants do not coincide (in other words the transition time associated with the auto-stereoscopic reference screen is different from the transition time associated with an auto-stereoscopic screen to be calibrated 1b, 1c) is that at least one of the screens to be calibrated 1b, 1c is not in phase with the reference screen 1a and must be adjusted.

Adjustments Three scenarios can arise, which correspond to three possible types of adjustment: 1st case, the transition from a first elementary image In, nEQ1, N]] to a second elementary image / (n + 1) dnodutoW on the reference screen corresponds to a transition from a first elementary image Im, mEQ1, ivJ, m # n to a second elementary image (m + i) dnoduloW on the screen to be calibrated 1b, 1c. In other words, the pairs of scanned views are different between the screens. This case can be adjusted by a software correction, the adjustment is then a permutation of the views on the screen to be calibrated 1 b, 1 c (the views are shifted by m-n ranks). 2nd case, the transition on the screen to calibrate 1 b, lc is not to the image associated with the next view (I (n + i) unoduiow), but to the image associated with the previous view (I (n + i) n_1) rodulor /). This means that the screen to calibrate 1b, lc is placed upside down, the adjustment is then a reversal of this screen. In this case, the pairs of elementary images coincide, but the transition moments are slightly shifted (and not synchronized).

The adjustment to be implemented is then a slight modification of the orientation of the screen to be calibrated 1b, 1c.

In the third case, which is the case encountered in the great majority, the adjustment of the screen can be done either manually by an operator, or by means of orientation 5 (see Figure 3) equipping the screen to calibrate 1b, 1c for which adjustment is necessary. These orientation means 5 consist in particular of servo motors for the rotation of a screen around a pivot axis of vertical axis, and are connected to the data processing means 4. The rotation to be applied to the screen to be calibrated 1b, 1c is then advantageously calculated (then transmitted to the orientation means 5) by the data processing means 4 as a function of the difference observed between the moment of transition associated with the auto-stereoscopic screen of reference 1a and the transition time associated with the auto-stereoscopic screen to be calibrated 1b, 1c, which makes the calibration completely automatic. It should be noted as previously explained that several screens 1b, 1c can be simultaneously calibrated. In this case, for each of these screens 1b, 1c the associated transition time is compared to the transition time associated with the auto-stereoscopic reference screen 1a. Following each comparison an adjustment is made or not. Advantageously, following one or more adjustments made, the method comprises the repetition for verifying the steps of displaying the stereoscopic reference image, video sequence acquisition, and image analysis. If a difference in transition instants is still observed, the method is repeated as long as the transition time associated with the auto-stereoscopic reference screen 1 a does not coincide with the transition time associated with each screen. stereoscopic to calibrate 1 b, lc. Successive Calibrations As explained previously, it is possible to calibrate a large number of screens 1b, 1cc, step by step. Indeed, it is not possible for the digital camera 2 to simultaneously observe a large number of screens. With reference to FIG. 3, first and second auto-stereoscopic screens 1b, 1c are to be calibrated with respect to the auto-stereoscopic reference screen 1a, the first and second auto-stereoscopic screens 1b, 1c being juxtaposed. The method thus comprises calibrating the first auto-stereoscopic screen to be calibrated 1b with respect to the auto-stereoscopic reference screen 1a and then calibrating the second auto-stereoscopic screen to be calibrated 1c with respect to the first auto-stereoscopic screen. to calibrate 1 b. It is thus sufficient to continue to move the camera 2 in the same direction (from left to right in Figure 3) to chain the calibrations. System & Computer Program Product According to a second aspect, the invention relates to the system for calibrating at least one auto-stereoscopic screen to be calibrated 1b, 1c with respect to an auto-stereoscopic reference screen 1a, each screen auto-stereoscopic 1 a, 1 b, 1 c being a multi-view screen capable of displaying a stereoscopic image composed of N interlaced images where each image corresponds to a view. As explained, the system comprises mobile video acquisition means 2 positioned (for example on a rail 3) so as to allow the simultaneous observation of said auto-stereoscopic screens 1a, 1b, 1c and means for processing video. data 4; the auto-stereoscopic screens 1a, 1b, 1c, the video acquisition means 2 and the data processing means 4 being configured for the implementation of the method according to the first aspect of the invention. The calibration system is used only once when screens are installed, and then disassembled. It can be reinstalled and reused when adding one or more additional screens later.

According to a third and a fourth aspect, the invention relates to a computer program product comprising code instructions for execution, when this program product is executed by data processing means 4 (for the image analysis part). and optionally adjustment of the screens), of a method for calibrating at least one auto-stereoscopic screen to be calibrated 1b, 1c with respect to an auto-stereoscopic reference screen 1a according to the first aspect of the invention, as well as storage means readable by a computer equipment on which a computer program product comprises code instructions for the execution of a method for calibrating at least one auto-stereoscopic screen to be calibrated 1 b, 1 c compared to an auto-stereoscopic screen reference 1a according to the first aspect.

Claims (12)

REVENDICATIONS1. Method for calibrating at least one auto-stereoscopic screen to be calibrated (1b, 1c) with respect to an auto-stereoscopic reference screen (1a), each auto-stereoscopic screen (1a, 1b, 1c) being a screen multi-view device capable of displaying a stereoscopic image composed of N interlaced images where each image corresponds to a view, the method being characterized in that it comprises steps of: (a) Display on said auto-stereoscopic screens (1a, 1 b, 1c) of a stereoscopic calibration image composed of N elementary images ik, kE litm interleaved; (b) Acquisition of a video sequence by mobile video acquisition means (2) positioned so as to allow simultaneous observation of said auto-stereoscopic screens (1a, 1b, 1c), said video sequence being acquired during a moving the video acquisition means (2) relative to said auto-stereoscopic screens (1a, 1b, 1c); (c) Analysis by data processing means (4) of said acquired video sequence so as to detect for each auto-stereoscopic screen (1a, 1b, 1c) a transition time of a first elementary image in, nE111 , NII corresponding to a first view, to a second elementary image I (n + 1) rodulor corresponding to the following view; (d) If the transition time associated with the auto-stereoscopic reference screen (1a) is different from the transition time associated with the auto-stereoscopic screen to be calibrated (1b, 1c), adjustment of the auto-stereoscopic screen to be calibrated (1b, 1c) so that the transition instant associated with the auto-stereoscopic reference screen (1a) coincides with the transition instant associated with the auto-stereoscopic screen to be calibrated (1b, 1c). 2. The method of claim 1, further comprising, in case of adjustment of the auto-stereoscopic screen to be calibrated (1b, 1c), the repetition of steps (a) to (c) as long as the time of transition associated with the auto-stereoscopic reference screen (1a) does not coincide with the transition time associated with the auto-stereoscopic screen to be calibrated (1b, 1c). 3. Method according to one of claims 1 to 2, wherein the displacement of the movable video acquisition means (2) is a translation on a rail (3) disposed along an axis parallel to the plane formed by the screen. stereoscopic reference (1a). The method of claim 3, wherein said translation axis is in the focal plane of the auto-stereoscopic reference screen (1a). 5. Method according to one of claims 1 to 4, wherein each reference image Ik is a uniform color image. 6. Method according to one of claims 1 to 5, wherein the adjustment of the auto-stereoscopic screen to be calibrated (1 b) consists in its reversal and / or in the modification of its orientation and / or in the permutation views. 7. Method according to claim 6, wherein the auto-stereoscopic screen to be calibrated (1b) is equipped with orientation means (5) that can be controlled by the data processing means (4), the adjustment of the auto-stereoscopic screen to be calibrated (1 b) consisting of the modification of its orientation as a function of the difference noted in step (d) between the transition time associated with the auto-stereoscopic reference screen (1a). ) and the transition time associated with the auto-stereoscopic screen to be calibrated (1b, 1c). 8. Method according to one of claims 1 to 7, wherein said transition is that of the reference image IN corresponding to the last view to the reference image / 1 corresponding to the first view. 9. Method according to one of claims 1 to 8, wherein at least a first and a second auto-stereoscopic screens (1 b, 1c) are to be calibrated with respect to the auto-stereoscopic reference screen (1a), the first and second auto-stereoscopic screens (1b, 1c) being juxtaposed, the method comprising calibrating the first auto-stereoscopic screen to be calibrated (1b) with respect to the auto-stereoscopic reference screen (1a), then calibrating the second auto-stereoscopic screen to be calibrated (1c) with respect to the first auto-stereoscopic screen to be calibrated (1b). 10. System for calibrating at least one auto-stereoscopic screen to be calibrated (1 b, 1c) relative to an auto-stereoscopic reference screen (1a), each auto-stereoscopic screen (1a, 1b, 1c) being a multi-view screen capable of displaying a stereoscopic image composed of N interlaced images where each image corresponds to a view, the system being characterized in that it comprises mobile video acquisition means (2) positioned so as to allow simultaneous observation of said auto-stereoscopic screens (1a, 1b, 1c) and data processing means (3); the auto-stereoscopic screens (1a, 1b, 1c), the video acquisition means (2) and the data processing means (4) being configured for carrying out the method according to one of claims 1 to 9. 11. Computer program product comprising code instructions for executing, when this program product is executed by data processing means (4), a method of calibrating at least one auto-stereoscopic screen to be calibrated (1b, 1c) with respect to an auto-stereoscopic reference screen (1a) according to one of claims 1 to 9. 12. Storage medium readable by a computer equipment on which a computer program product comprises code instructions for executing a method for calibrating at least one auto-stereoscopic screen to be calibrated (1 b, 1c) with respect to an auto-stereoscopic reference screen (1a) according to one of claims 1 to 9.