Device for stereoscopic pictures with a base-defining system.

The invention relates to stereoscopic shooting, for cinema or television, in the case where one or two objectives with variable focal length are used.

It is known to take stereoscopic shots with a variable distance between the two shooting points, this distance being called "base", and with a variable angle between the two viewing directions, this angle being called "convergence" ". The base is manually adjusted, according to empirical formulas, according to the focusing distance and the focal distance of the lens (s) used. The cameraman can also take into account the depth of field, to improve the relief effect, the appreciation of which remains subjective. The convergence is adjusted, manually, so that the two directions of view converge on the most interesting plane of the subject, but this adjustment is, too, quite subjective.

When the lenses used have a fixed focal length, the setting that is most often changed is the focus setting, so it is the one that will most often cause the cameraman to change the base and convergence. But when the lenses have a variable focal length, in other words are "zooms", it is also necessary to modify the setting of the base and of the convergence, when the focal length is varied.

It is well known that when a shooting without relief is carried out with a telephoto lens, or with a wide angle, the restored perspectives seem false compared to the natural perspectives. With a telephoto lens the different planes of the image seem to be closer to each other. On the contrary, with a wide angle the different planes of the image seem to be more distant from each other. In the case of stereoscopic shots and the reproduction of stereoscopic images, these distortions of the perspectives are even more troublesome for the observer if the base is unchanged.

The distortion of the perspectives causes a degradation of the effect of relief perceived by the observer, since it preserves the same angle of view, during the restitution of the image, whatever the conditions in which the shooting has been carried out. The observer perceives an under-relief in the case where the shooting was made with objectives at long focal distance, and perceives an over-relief in the case where the shooting was carried out by objectives at short distance focal.

It is known to remedy the degradation of the relief effect, in the case of the use of objectives with fixed focal distances, by manually adjusting the distance between the two shooting points according to empirical formulas which depend on the focal length of the lenses used, in order to increase or decrease the impression of relief according to the compensation to be achieved. This adjustment can be done manually and according to the same formulas when using zoom lenses. However, for film and television, these adjustments reach a complexity too great to be correctly executed by the cameraman, when it comes to following a moving subject.

The device according to the invention includes a program memory and position controls for automatically adjusting, according to predetermined laws, the base and convergence, as a function of the focusing distance and mainly the focal distance, to facilitate the use of the zoom (s), for stereoscopic shots of cinema or television.

According to the invention, a variable-base stereoscopic picture taking device, comprising means for taking pictures from a first and a second point of view, separated by a variable distance B called base, according to two viewing directions forming an angle 0 called convergence, these means comprising at least one objective with variable focal distance, is characterized in that it further comprises:<ul id="ul0001" list-style="none"><li>- a lens control device, for controlling the adjustment of its focal distance, the adjustment of its focus, and the adjustment of its diaphragm;</li><li>- a device to control the convergence and control the base;</li><li>a device for controlling the servo device coupled to the device for controlling the objective in order to determine a convergence value and a base value, as a function of the objective settings according to a predetermined law stored in a memory.</li></ul>

The invention will be better understood and other details will appear with the aid of the description below and the accompanying figures:<ul id="ul0002" list-style="none"><li>- Figure 1 shows the block diagram of a first embodiment of the device according to the invention;</li><li>- Figure 2 shows another view of this first example;</li><li>- Figure 3 shows a sectional view of part of this first example;</li><li>- Figures 4, 5, and 6 show block diagrams of three other embodiments.</li></ul>

The embodiment shown in FIG. 1 comprises a mechanical and optical part, and an electronic part. The mechanical and optical part includes two identical zoom lenses 1 and 2, two television cameras 3 and 4, two axes of rotation 7 and 8 on which the cameras 3 and 4 are fixed respectively, two supports 5 and 6 in which the axes rotate 7 and 8, two guides 9 and 10 on which the supports 5 and 6 slide, and two motors 11 and 12. The two cameras 3 and 4 each take pictures of an object 0 placed in front of them.

In this example, the two viewing directions are formed by the optical axes of the zooms 1 and 2, which converge towards the point 0 at an angle 0. In this example, the base, which is the distance between the two shooting points, is equal to the distance B separating the optical centers from the zooms 1 and 2. A mechanical device makes it possible to control the convergence and the base to control signals determined as a function of the focus adjustment M, the focal length adjustment F, and the diaphragm adjustment D of the zooms 1 and 2.

The cameras 3 and 4 can rotate around a vertical axis, 7 and 8 respectively, to adjust the convergence of the viewing directions in a horizontal plane. The axes 7 and 8 are mounted on the supports 5 and 6 which can move horizontally on the guides 9 and 10 which consist of two rods parallel to each other, horizontal, and perpendicular to the planes of symmetry of the directions of view. The displacement of the supports 5 and 6 makes it possible to adjust the base B. The motors 11 and 12 allow this movement to be ensured as well as the rotation of the axes 7 and 8, according to a mechanism described below.

The electronic part of this exemplary embodiment comprises a device 17 for remote control of the zooms, a device 18 for controlling the device for controlling the convergence and for controlling the base, a device 19 for selecting a law for these controls. , and a device 21 for manual adjustment of the base and of the convergence. Professional television cameras are equipped with a zoom whose setting M of the focusing, the setting F of the focal distance, and the setting D of the diaphragm are carried out by an electric remote control made up of a position servo-control which recopies the position of a button operated by the cameraman. In this example, the device 17 is manipulated by the camera operator to provide the zooms 1 and 2 with three adjustment instructions M, F, D in the form of three voltages, and these instructions are applied at the same time to an input of the device 18. Conversely, three position sensors located in each of the zooms 1 and 2, and not shown in the figures, respectively supply three voltages to the device 17 to control the adjustments made.

The devices 21 and 19 each have an output connected respectively to an input of the device 18. The device 19 allows the cameraman to select a control law from among four predetermined laws, or else manual adjustment, by control buttons of the device 21 .

The device 18 comprises a microprocessor 13 connected by an address and data bus to a read-only memory 15, to a random access memory 16, and to an interface 14. The interface 14 has two inputs connected respectively to the outputs of the devices 19 and 21; a multiple input connected to an input-output of the device 17 to receive the values ​​of the setpoints of the settings M, F, D; and an input-output. This input-output, on the one hand provides control signals to the motors 11 and 12, and on the other hand receives signals supplied by position sensors translating the position of the supports 5 and 6 and the axes of rotation 7 and 8 , these sensors not being sho wn in the figures.

The device 19 for selecting a law makes it possible to select one from four laws making it possible to determine a value of the convergence and a value of the base as a function of the values ​​of the settings M, F, and D. Three of these laws are frozen and are stored in the read-only memory 15. One of them, which is the most used in practice, corresponds to a restitution of the most natural relief possible in all the conditions of shooting. For example, this law can be deduced from the formulas stated by General Hurault in his work entitled "Problèmes Techniques de la Photographie Stereoscopique" published by the National Geographic Institute in 1964. This book gives, on page 119, a formula allowing to determine the basis of a stereoscopic shot. This formula is established by considering that a difference in angular paralaxis of 3 ° between the foregrounds and the backgrounds can be considered acceptable for almost all observers. When this value o f difference in angular paralaxis is exceeded, binocular fusion is no longer possible in all the space reconstituted in artificial vision in a stereoscope or on a screen, except for certain observers having a lot of training to vary the convergence of their fixing line, leaving their constant accommodation. The author deduces the following formula, which gives the value of the base B as a function of the distance D between the camera and the first plane observed and of the distance D₂ the distance between the camera and the second plane observed, these values ​​being expressed in meters:<maths id="math0001" num=""><img file="EP0146476A2_D0001.tif" /></maths>

The demonstration of this formula is made on the assumption that the difference in angular paralaxis of 3 ° allows to obtain a significant effect of relief but not tiring for an average observer and that the focal distance of the camera is identical to the focal length of a stereoscope used for the reproduction of views. A similar formula can be demonstrated taking into account the focal length f_p of the camera and the focal length f of the stereoscope:<maths id="math0002" num=""><img file="EP0146476A2_D0002.tif" /></maths>

In the case of shooting with objectives with variable focal length the value f varies but also the values ​​D₁ and D₂ because the depth of field is determined by the focal length and the aperture of the shooting lenses. The focal length f of the stereoscope is a constant value which is replaced by an equivalent value in the case of restitution of the images by projection on a diffusing screen or on a television screen. The law stored in the read-only memory 15 is therefore of the form:<maths id="math0003" num=""><img file="EP0146476A2_D0003.tif" /></maths>

D_i(M, F, D) and D₂(M, F, D) are respectively the distance between the camera and the first sharp plane and the distance between the camera and the last sharp plane, and are determined according to the values ​​M, F, and D by a conventional calculation in optics or are read in tables stored in read-only memory after having been calculated by the classical formulas of optics or else after having been determined experimentally. The coefficient A is a constant coefficient which is determined experimentally, which depends on the importance of the desired relief effect and which depends on the conditions of observation of the restored images: the dimensions of the screen and the distance of the spectators from on this screen. Two other predetermined laws are stored in the read-only memory 15 and correspond to a coefficient A of double value and to a coefficient A of half value, to obtain respectively an effect of over-relief or to obtain an effect of under-relief.

A fourth law can be stored in the random access memory 16 by a learning process consisting in carrying out test shots with manual adjustment by the device 21, during repetitions of the scene, then in storing the values ​​of the convergence and of the base according to the value of one of the parameters, for example the setting M of the focusing. The learning function of the device 18 is controlled by the cameraman using manual controls integrated into the adjustment device 21. During the effective shooting the cameraman selects the fourth law by the selection device 19 and he acts on the zoom settings 1 and 2 without being concerned with the effect of relief to be obtained by acting on the base and the convergence, the servo control device 18 achieves this effect as a function of the focus adjustment value. The speed at which the effect takes place can be much faster than the speed at which learning has taken place, without difficulty for the cameraman.

The work of the cameraman is as easy as in the case of a conventional camera since he has selected one of the laws automatically determining the convergence and the base. It only takes care of controlling the conventional adjustments of focus, focal length and diaphragm. This simplification of his work allows him to easily take good quality stereoscopic shots on a moving object, especially when it is moving towards the cameras.

FIG. 2 represents a front view of part of this first exemplary embodiment, showing from the front the cameras 3 and 4 with their zooms 1 and 2, and the whole of the device for servoing the base and servo of convergence. The cameras 3 and 4 pivot in the horizontal plane by being driven by the vertical axes 7 and 8 and by relying on ball bearings 21 and 28 placed on the upper face of the supports 5 and 6, these supports 5 and 6 having each the shape of a cubic cage.

Figure 3 shows a section along a vertical plane AA of the support 5. The support 6 is similar. The operation of this mechanical device will be better understood by referring simultaneously to Figures 2 and 3. The supports 5 and 6 are guided horizontally by the guides 9 and 10 which are parallel and horizontal cylindrical rods. The supports 5 and 6 are moved along the guides 9 and 10 by a shaft 22 parallel to the guides 9 and 10, of the same length, and carrying a different screw pitch over a first and a second half of its length. The shaft 22 passes through two opposite walls of each of the supports 5 and 6 by threaded holes which ensure the drive of the supports in two opposite directions when the shaft 22 is in rotation. This rotation is ensured by the motor 11.

The pivoting of the vertical axis 7 is ensured by a toothed wheel 26 fixed on this shaft and meshing in an endless screw 24. The endless screw 24 has a square section hole along its axis of symmetry, through which passes a shaft 23, of the same section, which is horizontal, parallel to the guides 9 and 10, of the same length. The shaft 23 is driven by the motor 12, it drives the worm 24, to cause the rotation of the shaft 7 supporting the camera 3.

A worm 20 whose propeller is in the opposite direction to that of the worm 24, is rotated by the same shaft 23 to drive a toothed wheel, not shown, identical to the wheel 26 and integral with the rotation shaft 8, in a direction opposite to the direction of rotation of the shaft 7. The worms 24 and 20 are integral in translation with the supports 5 and 6 because they are held by bosses 25 preventing the displacement of the worms 24 and 20 parallel to the guides 9 and 10 when they exert a force on the cogwheels, such as wheel 26, to rotate the cameras.

The worms 20 and 24 not being immobilized in translation on the shaft 23 they do not prevent the translation of the supports 5 and 6 under the action of the shaft 22. The guides 9, 10, the shafts 22 , 23, and the motors 11, 12 are mounted on. flanges 70 and 71, connected by a bottom 72. This simple mechanical device makes it possible to adjust the base and adjust the convergence without having to double the servo devices regulating the position of the cameras. In this exemplary embodiment, the minimum value of the base corresponds to an approximation of the cameras such that their walls are in contact. It is advantageous to plan their construction in such a way that the zooms 1 and 2 are mounted as close as possible to the walls which will be in contact when the base is minimal.

When the cameras are very bulky, the movement of the cameras by a device for controlling the convergence and for controlling the base requires a robust and powerful device. It is then advantageous to use additional optical devices making it possible to keep these cameras stationary, compared to the device providing a servo of the base and of the convergence.

FIG. 4 shows a second embodiment of the device according to the invention, comprising two television cameras 30 and 31 provided with zoom lenses 32 and 33, fixed relative to a device 42 for controlling the base and the convergence similar to the device represented in FIGS. 1 to 3, but where instead of moving the cameras 30 and 31 the supports 40 and 41 move plane mirrors 38 and 39. These mirrors are vertical and rotate around vertical axes 57 and 58 similar to axes 7 and 8. When the convergence is zero the mirrors 38 and 39 make an angle of 45 ° relative to the plane of symmetry of the directions of view. The cameras 30 and 31 are arranged symmetrically with respect to this plane of symmetry and receive the light coming from two viewing directions 36 and 37 via the mirrors 57 and 58 respectively and from two deflection mirrors 34 and 35 respectively. The mirrors 34 and 35 are vertical plane mirrors which are parallel to the mirrors 38 and 39 when the convergence is zero. In this example, convergence is determined by the angle of rotation of the mirrors 38 and 39, which rotate in opposite directions.

In the previous examples the optical paths followed by the light coming from the two viewing directions are symmetrical with respect to the plane of symmetry of these two directions, they are therefore identical. FIG. 5 represents a third embodiment example where the two optical paths are not strictly the same length. This is not a problem if the shots are not taken very close to the object, because the depth of field makes it possible to have two views as sharp as each other and the difference in magnification is small . It is also possible to artificially lengthen the shortest optical path by an optical device the realization of which is within the reach of those skilled in the art, or else to modify the focal distance of one of the zooms for a constant coefficient. applied to the setpoint F for adjusting its focal distance.

In FIG. 5, two television cameras 43 and 44, provided with zoom lenses 45 and 46, are arranged in such a way that their optical axes are parallel and horizontal. The camera 44 directly receives the light corresponding to a first view direction 48. The camera 43 receives the light corresponding to a second view direction 47 by means of a movable mirror 50 and a deflection mirror 49. The movable mirror 50 is a vertical plane mirror rotating around a vertical axis under the action of a motor 54 carried by a support 51 moving horizontally on rectilinear guides 55 and 56 under the action of a threaded shaft 57 driven by a motor 53. Position sensors not shown measure the position of the movable mirror 50 and of the support 51.

The horizontal movement of the support 51 moves the mirror 50 in the plane of the optical axes of the cameras 43 and 44 and perpendicular to them to vary the base. The rotation of the mirror 50 makes it possible to vary the convergence. When the convergence is zero, the mirrors 49 and 50 are parallel and each make an angle of 45 ° relative to the optical axes of the cameras 43 and 44. The electronic part of the device is similar to that of the first embodiment.

The device according to the invention can be applied to taking stereoscopic views according to a method using a single camera and a single objective. FIG. 6 represents a fourth exemplary embodiment, implementing the known method of anaglyphs, and comprising a single camera 66 provided with a zoom 65 receiving the light coming from two directions of distinct views 67 and 68 respectively via d 'a deflection mirror 63 and a dichroic blade 64 placed on the optical axis of the camera 66. The mirror 63 is a vertical plane mirror rotating around a vertical axis under the action of an axis 69 similar to the axis 7 of the first embodiment. The dichroic blade 64 is plane and vertical, and it rotates around a vertical axis under the action of an axis 70 similar to the axis 8 of the first example. The axes 69 and 70 are carried by supports 61 and 62 similar to the supports 5 and 6 of the first example, mQs by a device 60 for controlling the base and for controlling the convergence, similar to that described in the first example . The optical axis of the camera 66 is in the extension of the direction of translation of the supports 61 and 62. When the convergence is zero the mirror 63 and the blade 64 are parallel and make an angle of 45 ° relative to the axis camera optics 66. The latter is fixed relative to the servo device 60.

The invention is not limited to the exemplary embodiments described above, many variants are within the reach of those skilled in the art because there are numerous optical devices making it possible to take pictures with a variable base and variable convergence, and these devices are generally easy to adapt to control the settings of the base and of the convergence, by a device similar to that described for the first example.

It is possible to realize these servos differently, for example by using stepping motors, controlled by a determined number of current pulses, which avoids the use of position sensors.

The invention applies to stereoscopic shooting for cinema and raised television.