IMAGE STABILIZING APPARATUS FOR A PORTABLE VIDEO CAMERA

Abstract: The image stabilization apparatus for a portable video camera is such that for angular variations about the optical axis (OZ) of the camera, the horizontal and vertical deflection currents Ix and Iy of the camera are converted as a function of these variations by an angular measurement device integrally connected with the camera prior to being applied to the corresponding horizontal and vertical coils (4 and 5, respectively) of the camera.

Description: Image stabilizing apparatus for a portable video camera BACKGROUND OF THE INVENTION The invention relates to an image stabilizing apparatus for a portable video camera. With the advanced miniaturization of video cameras, these cameras are becoming lighter and lighter in weight and can be carried by hand. Hence it can happen that if an operator viewing a predetermined subject moves, a slight displacement of the image of the subject on the target plate of the camera occurs; this translates into a corresponding displacement of the image on the receiver, resulting in a blurred image on the screen. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration of a portable video camera; Fig. 2, on a larger scale, shows the target plate of the video camera of Fig. 1; Fig. 3 is a block diagram of an embodiment of the image stabilizer according to the invention; Fig. 4 is a block diagram of another embodiment of image stabilizer; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 schematically shows a portable video camera and its main components, for the sake of better comprehension of the invention. Hence the video camera includes an objective or lens 1, a target plate 2, an electron gun 3 and horizontal deflection coils 4 for scanning in the x direction and vertical deflection coils 5 for scanning in the y direction, although these coils may also be deflection plates. As is well known, a subject 6 outside the camera forms an optical image 7 on the target plate 2 of a video camera, and this optical image is scanned by the cathode reading system of the camera with the aid of an electron beam emitted by the electron gun 3, which is deflected horizontally and vertically by the deflection coils 4 and 5 having vertical and horizontal fields, respectively. Fig. 2, in broken lines, shows the target plate 2 that has undergone a rotation about the optical axis OZ of the camera. It should be noted here that to obtain compensation for the displacements of the position of the image on the target plate, i.e., its stabilization, it is necessary that the target area should be greater than the area of the optical image projected on it by means of the objective or lens 1. The position of the target plate 2 of the camera may be defined in Cartesian coordinates, using a system of axes, x, y and z. First, let it be assumed that between a time 0 and a time t, the camera has undergone an angular variation about its optical axis OZ. A point in the optical image 7 on the plate 2 is defined at time 0 by its coordinates xg, yg, z. When this point has rotated by the angle γ about the axis OZ, it is then defined by x t , y t , z (z is unchanged). In order that the angular variation γ will have no effect at all upon the output signal of the camera, that is, will definitively not affect the position of the image with respect to the screen on the receiver, this angular varia¬ tion must be compensated for and the cathode reading system of the camera must be made to rotate about the same angle γ. Let Ix and ly represent the currents that allow the vertical field and horizontal field of the deflection coils 4 and 5 to be created; in the absence of angular displacements of the camera, Ix, ly are thus x and y scanning deflection currents for a camera lacking the image stabilization apparatus,"according to the invention. In order to effect the required compensation described above, converted signals Ilx and Ily must be sent through the coils 4 and 5, respectively, the values of these signals being as follows: Ilx = Ix cos γ + ly sin γ Ily = ly cos γ - Ix sin γ The signals Ix and ly are generated by the camera, and the signals sin γ and cos γ can be generated by a sine and cosine converter associated with a rate gyroscope integrally connected with the camera and placed in such a manner that it provides a measure of the angular velocity of the camera about the axis of its objective. The entire apparatus thus functions as a vibration or oscillation damper for an elastically suspended camera. In Fig. 3, which shows a block diagram of the ap¬ paratus, a rate gyroscope 10 has been shown, which is integrally connected to the camera of Fig. 1 and is located in such a manner that it provides a measure of the angular velocity of the camera about the axis OZ of its objective. The rate gyroscope 10 is connected at the output to an in¬ tegrator 11 provided with a slow return to zero, so as to convert the angular velocity into an angle for rapid move- ents. This integrator is connected to a converter 12 of sine and cosine functions, which in turn is connected to a linear function converter circuit 13. At its output, the converter 12 thus furnishes two values, sin γ and cos γ, which are proportional to the sine and cosine of the angles of inclination of the camera with" respect to its prior position, for rapid angular variations, and furnishes an increasingly reduced fraction of these functions when the angular velocity decreases. The sine and cosine converters mentioned above can be replaced by con- verters operating upon the angle measured by the gyroscopic device to obtain polynomials or power series (Taylor) thereof respectively corresponding to these functions, which may use, in a first approximation, the first-order (linear) member only. If more precision is desired, higher-order polynomials may be used. The linear function circuit 13 is connected to the output of the circuit of the camera that furnishes the signals Ix and ly, this circuit being shown at 14. The linear function circuit 13 comprises a multiplier and adder circuit suitable for performing multiplications and addi¬ tions of signals, so that the above-mentioned converted signals Ilx and Ily can be obtained. Multiplications and additions in this manner of signals generated on the one hand by the camera, relating to Ix and ly, and on the other hand by the ' rate gyroscope, the integrator and the converter relating to γ, are very easily performed in real time by analog or numerical circuits of a known type. It has been assumed above that the camera is angularly displaced about the optical axis OZ of its objective. Let it now be supposed that the camera is displaced about an axis perpendicular to the optical axis of the camera, for example about the axis x of Fig. 2, which is in the horizontal plane. Any rotational movement α about the axis x is translated into a displacement of the optical image 7 in the direction y, which is proportional to the angle α (small α) . In order to prevent such a rapid displacement of the optical image 7 from being translated into a corresponding displacement of the electronic image at the receiver, a direct current proportional to α must be added to the vertical scanning current ly. Thus the cathode ray corresponding to a point is made to coincide with this point independently of the aforementioned rotational movement. The converted signal thus assumes the following value: Iiy = ly + Klα An identical induction for a rate gyroscope, with which, after integration, angular varations β about the y axis of Fig. 2 can be obtained, demonstrates that the converted signal is then as follows: Iix = Ix + K2β The use of such a converted signal is not generally necessary, because the shocks to which the cameras are subjected as they move are seldom diminished by movements about the y axis that displace the image in the x direction proportional to the angle β. Fig. 4 shows the entire stabilization apparatus for arbitrary angular variations of the camera making use of the aforementioned provisions. Any angular variation of the camera is defined in polar coordinates by the angles α, β and γ above, so that the apparatus thus includes three rate gyroscopes 10a, 10b, 10c similar to the rate gyroscope 10 of Fig. 2, which are provided in order to furnish information corresponding to the angular variations γ, α and β, respectively. The coefficients Kl and K2 multiplying the angles by which the camera pivots about a horizontal and vertical axis, respectively, both of which are perpendicular to the optical axis OZ, depend on the distance for which the objective focuses the image of the subject onto the photosen¬ sitive surface of the target plate, because this determines the displacement of the optical image in the target plane. If a zoom lens, which is capable of varying the focal length of the objective, is used, the coefficients Kl and K2 are made variable as a function thereof. In order to obtain this, as shown in Fig. , the zoom lens, which is controlled by rotation about the optical axis, is mechanically coupled (by gears or a belt and pulleys) to the wiper shaft of a potentiometer whose resistive path is connected between the terminals of a DC power supply, in order to deliver a voltage that is variable with the adjustment of the zoom lens. If the variations in the focusing of the zoom lens are nonlinear with the angle of rotation of its control device ' , the resistor of the potentiometer can be made to follow this nonlinear function. It is also possible to connect two such potentiometers, connected in the manner of rheostats, into the feedback path of two operational amplifiers, which respectively amplify the signals given by the two further gyroscopic devices (cascaded rate gyroscopes and in¬ tegrators), in order to vary the respective gains of these amplifiers. The various rate gyroscopes 10a, 10b, 10c are connected to integrators 11a, lib, lie, which in turn are connected to converters 12a, 12b, 12c. The converter 12a is a sine and cosine function converter, while the converters.12b and 12c respectively furnish a direct current Klα and K2β propor¬ tional to- the angular variation detected by the correspond¬ ing gyroscope. A linear function circuit 13', which receives the signals Ix and ly from a circuit 14' that is identical to the circuit 14 of Fig. 3, is connected to the output of the converters 12a, 12b and 12c. The linear function circuit 13' thus furnishes at its output signals that are the linear functions of Ix, ly, sin γ, cos γ, α and β as defined above. These signals are applied to the deflection coils 4 and 5 of Fig. 1 and can be written as follows: I2x = Ix cos Y + ly sin γ + K2β I2y = ly cos γ - Ix sin γ + Klα In the case where the deflection via a coil is replaced with a static deflection, the same induction must naturally be applied, in order to proceed to the linear operations described above on the voltages applied to the deflection plates. It should be noted that in the entire foregoing descrip¬ tion, the dimensions of the image 7 furnished by the objec- tive 1 and the target plate 2 of the camera must be such that the above values of the converted signals remain within the boundaries of the target plate. Moreover, a switch located on the camera makes it possible to prevent functioning of the stabilization ap- paratus except when this is deemed useful. If the " camera uses a charge-coupled device solid-state picture sensor, shown in Fig. 5 , the scanning is carried out in a matrix fashion, using a digital computer or micro¬ processors. The linear vertical and horizontal deflection of the scanned image field or of the starting point of the scan are relatively simple operations on the addresses of the read-out points. However, the rotation of the image about the optical axis of the camera is a more complex operation, because in order to obtain a line, several rows of the CCD elements have to be read consecutively. As a matter of fact, depending on the value of the angle of rotation (γ) a certain number of successive elements of the nth row will have to be read, then the same number of elements of the (n + l)th and so on, until the end of each line. Thereafter, the following (n + l)th o (n + 2)th row (if the scan is interlaced) is read in the same manner as before, by passing from one row to the next. If the rotation is in the opposite direction, the elements of the nth row are followed by the (n - l)th and then by the (n - 2)th, and so on. An adequate algorithm can be stored in a read-only memory associated with a micro¬ processor, to carry out the desired shift in the address of the read-out. The shift functions will correspond substan¬ tially to the sine and cosine of the angle of rotation. The present disclosure relates to the subject matter disclosed in French Application 87/00720 of January 22, 1987, the entire specification of which is incorporated herein by reference. It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the dependent claims. The word "gyrometre" actually means a "rate gyro¬ scope" or "rate gyro" which generates a signal propor¬ tional to the angular velocity of the rotation of the camera about its optical axis (a rate gyro being a gyroscope whose gi bal is restrained into a fixed posi¬ tion relatively to the object on which it is mounted by means of drawsprings and whose motion is damped) . The signal is integrated in an integrator having a slow dis¬ charge rate (return to zero) to give an output signal proportional to the angle of rotation. Any other type of instrument (transducer) giving a voltage proportion¬ al to the angular displacement of the camera may be used. In an experimental model of the invention a gyro¬ scope for model airplanes was successfully applied. The invention overcomes this problem by creating an image stabilizer for a portable video camera such that angular variations in the axis of the camera do not affect the output signal of the camera; that is, they definitively do not affect the position of the image with respect to the screen of the receiver. In accordance with the invention, the apparatus for stabilizing images for a portable video camera is charac¬ terized in that for an angular variation about the optical axis of the camera, and for vertical deflection currents Ix and horizontal deflection currents ly of the camera in the absence of stabilization, the deflection currents are converted and take the following form: Ilx = Ix cos γ + ly sin γ ily = ly cos γ - Ix sin γ where Ilx is the converted horizontal deflection current, and Ily is the converted vertical deflection current, which are applied respectively to the corresponding horizontal and vertical deflection coils of the camera. In accordance with other characteristics of the inven¬ tion, the converted signals can also take into account rotational movements about a horizontal axis and a vertical axis perpendicular to the axis of the objective, or lens. Various other characteristics of the invention will become more apparent from the ensuing detailed description of ex¬ emplary embodiments- of the invention, taken in conjunction with the drawings. It is understood that these exemplary embodiments are not to be considered as limitin

Claims: WHAT IS CLAIMED IS: 1. An image stabilization apparatus for a portable video camera, characterized in that for angular variations about any axis of the camera, the image analysis devices (for example, horizontal and vertical scanning devices) are augmented with an angular measurement device and a cal¬ culator acting upon the corresponding devices of the camera, in order to assure the immobility of the recorded or trans¬ mitted image. 2. An image stabilization apparatus for a portable video camera, characterized in that for angular variations γ about the optical axis (OZ) of the camera, and for vertical deflection currents Ix and horizontal deflection currents ly of the camera in the absence of stabilization, the deflec¬ tion currents are converted by an angular measurement device integrally connected with the camera and take the following form: Ilx = Ix cos Y + ly sin γ Ily = ly cos γ - Ix sin γ where Ilx is the converted horizontal deflection current, and Ily is the converted vertical deflection current, which are applied respectively to the corresponding horizontal and vertical deflection coils (4 and 5, respectively) of the camera. 3. An image stabilization apparatus for a portable video camera, characterized in that for angular variations α about a horizontal axis (x) perependicular to the axis (OZ) of the objective and for a vertical deflection current (ly) of the camera in the absence of stabilization, the vertical deflection current applied to the vertical deflection coil (5) is converted by an angular measurement device integrally connected to the camera and takes the following form: Iiy = ly + Klα. 4. An image stabilization apparatus for a portable video camera, characterized in that for angular variations β about a vertical axis (y) perpendicular to the axis (OZ) of the -objective and for a horizontal deflection current Ix of the camera in the absence of stabilization, the horizontal deflection current applied to the horizontal deflection coil (4) is converted by an angular measurement device integrally connected to the camera and takes the following form: Iix = Ix + K2β. 5. An image stabilization apparatus for a portable video camera in accordance with all of the claims 1-3, characterized in that for an arbitrary angular variation of the camera, the vertical and horizontal deflection currents applied to the horizontal and vertical deflection coils (4 and 5, respectively) via an angular measurement device integrally connected with the camera are the linear functions of Ix, ly, sin γ, cos γ, and β obtained via an integrator receiving the signals and can be written as follows: I2x = Ix cos γ + ly sin γ + K2β I2y = ly cos γ - Ix sin γ + Klα. 6. An image stabilization apparatus for a portable video camera dependent on one of the claims 1-4, charac¬ terized in that the angular measurement device integrally connected with the camera includes at least one rate gryo- scope (10) -connected to an integrator (11) connected to an analog or numerical converter (12), the output of which is connected via a linear function circuit (13) to the coils (4 and 5) or to the horizontal and vertical deflection plates of the camera.

Inventors: FOURNIER ANTOINE, FOURNIER, ANTOINE
Applicants: FOURNIER ANTOINE, FOURNIER, ANTOINE
Application year: 1988
Main classification: H04N5
IPC codes: H04N5