Patent Publication Number: US-2010123783-A1

Title: Gain calibration device and method of gain calibration

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a gain calibration device and a method of gain calibration, and particularly relates to a gain calibration device and a method of gain calibration adapted for an optical image stabilizer. 
     2. Description of Prior Art 
     With the rapid development of information technology, more and more types of consumer electronics products, such as computers, LCD TVs, videos, digital cameras, have been popularized. Especially, with light, thin, short, small features, digital camera is very convenient to carry, and photographs are also getting higher and higher pixel. To get a better quality shot, during finding a view, it is important to adjust an image zoom position inside the lens (for example, charge-coupled device (CCD)) back and forth, that is, it requires adjusting the magnification of the camera lens to shoot people or objects with more clearly focus. At this point, based on the gyro signal gain adjustment, the camera can be in a stable condition by an optical image stabilizer. However, the gyro signal gain value and the camera magnification influence each other, and therefore, when the magnification of the camera changes, the gain value adjustment should be changed simultaneously. 
     In prior arts, within a specified range of magnification, the camera uses a fixed gain value. Taking a camera having a magnification of 12× as an example, when magnification of the camera lens is set to 1× to 3×, the gain value is 10; when magnification of the camera lens is set to 4× to 6×, the gain value is 20; and when magnification of the camera lens is set to 7× to 12×, the gain value is 30. Although three different magnifications are included in the range of 1× to 3×, the gain value maintains same, and this is similar in the magnification ranges of 4× to 6× and 7× to 12×, where the gain values are same respectively. Consequently, gyro signal cannot be properly compensated, resulting in poor image quality. In view of this, it is necessary to develop a novel optical image stabilizer, to solve the above-mentioned problem. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a gain calibration device and a method of gain calibration, which are capable of compensating, rapidly and accurately, a gain value of an optical image stabilizer of an image processing equipment to improve the image quality. 
     To achieve the above objectives, the invention provides a gain calibration device, which comprises an integrator, a first register, a controller, and a second register. The gain calibration device is employed in an optical image stabilizer (OIS) of an optical imaging system. The integrator is provided for receiving a gyro signal and integrating the gyro signal to form integral information. The first register is used to store the gyro signal, the integral information, and at least one reference magnification of the image processing equipment, wherein the at least one reference magnification is corresponding to at least one reference gain value of the optical image stabilizer. The second register functions for temporary storage of a current gain value. The controller determines whether a current magnification of the image processing equipment is the same as a previous magnification. When the current magnification is not the same as the previous magnification, the controller reads the current magnification from the image processing equipment. Based on the at least one reference magnification, the at least one reference gain value and the current magnification, the controller calculates the current gain value corresponding to the current magnification by interpolation, and replaces a last current gain value temporarily stored in the second register with the current gain value. When the current magnification is the same as the previous magnification, the controller compensates continually the optical image stabilizer by the gain value corresponding to the current magnification. 
     The present invention also provides a method of gain calibration, which comprises the following steps: 
     (a) the image processing equipment activating stabilizing mechanism of the optical image stabilizer; 
     (b) the integrator integrating a gyro signal to form integral information; 
     (c) the first register storing the gyro signal and the integral information; 
     (d) the controller determining whether a current magnification of the image processing equipment is the same as a previous magnification, wherein when the current magnification is not the same as the previous magnification, the controller reads the current magnification from the image processing equipment, and when the current magnification is the same as the previous magnification, the controller compensates continually the optical image stabilizer by the gain value corresponding to the current magnification and performs continually the step (d) for determination of magnification changes; 
     (e) the first registers storing at least one reference magnification of the image processing equipment, the at least one reference gain value of the optical image stabilizer being corresponding to the at least one reference magnification of the optic image stabilizer, the second register storing a current gain value; 
     (f) based on the at least one reference magnification, the at least one reference gain value, and the current magnification, the controller calculating the current gain value corresponding to the current magnification by interpolation, and replacing a last current gain value temporarily stored in the second register with the current gain value; and 
     (k) the second register compensating continually the optical image stabilizer by the current gain value corresponding to the current magnification. 
     The present invention may best be understood through the following description with reference to the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an optical image stabilizer having a gain calibration device in accordance with an embodiment of the present invention; 
         FIG. 2  is a curve diagram illustrating characteristics of magnification of the image processing system shown in  FIG. 1  in relation to gain value of the optical image stabilizer; and 
         FIGS. 3A-3D  are flow charts of a method of gain calibration according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , which shows a block diagram of an optical image stabilizer  102  having a gain calibration device  100  in accordance with an embodiment of the present invention, the gain calibration device  100  couples a gyro sensor  104  to a vibration compensation module  124 . The gain calibration device  100  outputs a gain-adjusted gyro signal to the vibration compensation module  124 . The gain calibration device  100  is employed in an optical image stabilizer (OIS) of an image processing equipment, such as a digital camera, a digital videos, or any other image processing equipment having an optical image stabilizer. The gain calibration device  100  comprises an integrator  110 , a first register  112 , a controller  114 , and a second register  116 . In an embodiment, the gain calibration device  100  is implemented by for example any of a micro control unit (MCU), a digital signal processor (DSP), a central processing unit (CPU), a complex programmable logic device (CPLD), a field programmable gate array (FPGA), and a system on-chip (SOC), or any combination of the above implementations. The vibration compensation module  124  comprises an optical image stabilizer platform  106 , a position sensor  108 , a summing device  118 , a filter  120 , and a motor drive  122 . 
     In the gain calibration device  100 , the integrator  110  receives a gyro signal and performs integration on the gyro signal to form integral information. In an embodiment, the integrator  110  calculates the integral of the gyro signal (such as angular velocity) with reference to time, so that the unit of the integral information is the same as the unit of output from the position sensor  108 . The first register  112  is used to store the gyro signal, the integral information, and at least one reference magnification of the image processing equipment, wherein the at least one reference magnification is corresponding to at least one reference gain value of the optical image stabilizer  102 . The second register  116  functions for temporary storage of a current gain value. The controller  114  determines whether a current magnification of the image processing equipment is the same as a previous magnification. When the current magnification is not the same as the previous magnification, the controller  114  reads the current magnification from the image processing equipment. Based on the at least one reference magnification, the at least one reference gain value, and the current magnification, the controller  114  calculates the current gain value corresponding to the current magnification by interpolation, and replaces a last current gain value temporarily stored in the second register with the current gain value, so that the second register  116  compensates and calibrates the optical image stabilizer  102  by the calculated current gain value. On the other hand, when the current magnification is the same as the previous magnification, the controller  114  compensates continually the optical image stabilizer  102  by the gain value corresponding to the current magnification. 
     It should be noted that, the first register  112  and the second register  116  can be for example two different memory sections or two different fields in a same storage component, for rapid read of the gyro signal (S gyro ), the integral information, the reference magnification, the reference gain value, the current magnification, and the current gain value, or alternatively, they can be, for example, memory sections or fields of two different storage components. Examples of the storage components include memories and memory cards. 
     In the vibration compensation module  124 , the position sensor  108  is provided for sensing the optical image stabilizer platform  106  to form a position signal, thereby compensating the optical image stabilizer platform  106 . The summing device  118  is provided for calculating the amount of compensation of adjusted gyro signal (S gyro ) and the position signal. The filter  120  is provided for filtering noises generated by the adjusted gyro signal (S gyro ) and the position signal. Based on filtered gyro signal (S gyro ) and filtered position signal, the motor drive  122  forms a drive signal to drive the optical image stabilizer platform  106 . 
     Referring to  FIGS. 1 and 2 ,  FIG. 2  is a curve diagram illustrating characteristics of magnification of the image processing equipment in relation to gain value of the optical image stabilizer. In a first embodiment, the first register  112  also stores current focal length of the current magnification and reference focal length of the reference magnification of the image processing equipment. Based on the ratio of the current focal length (fc) to the reference focal length (fr) multiplied by the reference gain value (Z 2 ), for example the focal length (fr) of the maximum magnification, the controller  114  calculates the current gain value (GC), which can be expressed by the following equation: GC=(fc/fr)*Z 2 . 
     In a second embodiment, the first register  112  further stores a first reference magnification (Z 1 ) and a second reference magnification (Z 2 ) of the image processing equipment, wherein the first reference magnification (Z 1 ) and the second reference magnification (Z 2 ) are corresponding to a first reference gain value (K 1 ) and a second reference gain value (K 2 ) of the optical image stabilizer  102 , respectively. Based on the first reference magnification (Z 1 ), the second reference magnification (Z 2 ), the first reference gain value (K 1 ), the second reference gain value (K 2 ), and the current magnification (ZC), the controller  114  calculates the current gain value (GC) corresponding to the current magnification (ZC) by interpolation. The first reference magnification (Z 1 ) is, for example, the minimum magnification of the image processing equipment and the second reference magnification (Z 2 ) is the maximum magnification of the image processing equipment. The current gain value (GC) calculation equation is as follows: GC=K 1 *[(Z 2 −Z 1 )/(ZC−Z 1 )]. 
     Based on the minimum magnification, the maximum magnification, the first reference gain value (K 1 ), the second reference gain value (K 2 ), and multiple additional current magnifications (ZC), the controller  114  calculates multiple additional current gain values (GC) corresponding to each of the multiple additional current magnifications (ZC) by interpolation, and the controller  114  establishes a look-up table with the current magnifications (ZC) and the current gain values (GC). The look-up table is stored in the first register  112 . Thus, when the image processing equipment is adjusted to a current magnification (ZC), a current gain (GC) corresponding to the current magnification (ZC) is used to compensate the optical image stabilizer  102 . 
     In the third embodiment, the first register  112  stores a first reference magnification (Z 1 ), a second reference magnification (Z 2 ), and a third reference magnification (Z 3 ) of the image processing equipment, wherein the first reference magnification (Z 1 ), the second reference magnification (Z 2 ), and the third reference magnification (Z 3 ) are corresponding to a first reference gain value (K 1 ), a second reference gain value (K 2 ), and a third reference gain value (K 3 ) of the optical image stabilizer  102 , respectively. The first reference magnification (Z 1 ) is, for example, the minimum magnification of the image processing equipment and the second reference magnification (Z 2 ) is the maximum magnification of the image processing equipment. 
     The controller  114  determines whether the current magnification (ZC) is between the first reference magnification (Z 1 ) and the third reference magnification (Z 3 ) or between the second reference magnification (Z 2 ) and the third reference magnification (Z 3 ). When the current magnification (ZC) is between the first reference magnification (Z 1 ) and the third reference magnification (Z 3 ), the controller  114 , based on the first reference magnification (Z 1 ), the third reference magnification (Z 3 ), the first reference gain value (K 1 ), the third reference gain value (K 3 ), and the current magnification (ZC), calculates the current gain value (GC) corresponding to the current magnification (ZC) by interpolation. The current gain value (GC) is calculated by an equation as follows: GC=K 1 *[(Z 3 −Z 1 )/(ZC−Z 1 )]. When the current magnification (ZC) is between the second reference magnification (Z 2 ) and the third reference magnification (Z 3 ), the controller  114 , based on the second reference magnification (Z 2 ), the third reference magnification (Z 3 ), the second reference gain value (K 2 ), the third reference gain value (K 3 ), and the current magnification (ZC), calculates the current gain value (GC) corresponding to the current magnification (ZC) by interpolation. The current gain value (GC) is calculated by an equation as follows: GC=K 3 *[(Z 2 −Z 3 )/(ZC−Z 3 )]. 
     During gain calibration, the gain calibration device  100  of the present invention employs the controller  114  to calculate different gyro gain value corresponding to each magnification, and each magnification corresponds to a different focal length. The present invention uses focal length and gain value of one magnification to quickly calculate a gain value of another magnification by interpolation, or uses one magnification or a number of different ranges of magnification to accurately calculate a gain value of another magnification. Consequently, the present invention can calibrate the gain value of each magnification and can effectively compensate gain of the optical image stabilizer  102 . Especially, when in the high-magnification state, gain value changes more significantly with the magnification. The present invention utilizes calculation or looks up a look-up table to associate each magnification with a gain value, thereby calibrating effectively gain value of the optical image stabilizer  102 . 
     Referring to  FIGS. 1 ,  2 , and  3 A- 3 D,  FIGS. 3A-3D  are flow charts of a method of gain calibration according to embodiments of the present invention. The gain calibration device  100  comprises the integrator  110 , the first register  112 , the controller  114 , the second register  116 , the summing device  118 , the filter  120 , and the motor drive  122 . The method of gain calibration is employed in the optical image stabilizer  102  of the image processing equipment and comprises the following steps: 
     Step S 300 : The image processing equipment activates the stabilizing mechanism of the optical image stabilizer  102 . 
     Step S 302 : The integrator  110  integrates a gyro signal to form integral information. 
     Step S 304 : The first register  112  stores the gyro signal and the integral information. 
     Step S 306 : The controller  114  determines whether a current magnification (ZC) of the image processing equipment is the same as a previous magnification, wherein when the current magnification (ZC) is not the same as the previous magnification, the controller  114  reads the current magnification (ZC) from the image processing equipment, and when the current magnification (ZC) is the same as the previous magnification, the controller compensates continually the optical image stabilizer  102  by the gain value corresponding to the current magnification (ZC) and performs continually Step S 306  for determination of magnification changes. 
     S 308 : The first registers  112  stores at least one reference magnification of the image processing equipment, the at least one reference magnification corresponding to at least one reference gain value of the optical image stabilizer  102 , the second register  116  storing a current gain value. 
     Step S 310 : Based on the at least one reference magnification, the at least one reference gain value, and the current magnification (ZC), the controller  114  calculates the current gain value (GC) corresponding to the current magnification (ZC) by interpolation, and replacing a last current gain value temporarily stored in the second register  116  with the current gain value. 
     Step S 312 : The second register  116  compensates gain of the optical image stabilizer  102  by the calculated current gain value (GC). 
     Step S 314 : Capturing an image is performed. 
     In the first embodiment shown in  FIG. 3B , Step S 400  is performed after Step S 308 . In Step S 400 , the first register  112  stores a current focal length of the current magnification and a reference focal length of the reference magnification of the image processing equipment. In Step S 402 , based on the ratio of the current focal length to the reference focal length and then multiplied by the reference gain value, the controller  114  calculates the current gain value (GC) and then the method goes back to Step S 312 . 
     In the second embodiment shown in  FIG. 3C , Step S 500  is performed after Step S 308 . The first register  112  stores a first reference magnification (Z 1 ) and a second reference magnification (Z 2 ) of the image processing equipment. The first reference magnification (Z 1 ) and the second reference magnification (Z 2 ) are corresponding to a first reference gain value (K 1 ) and a second reference gain value (K 2 ) of the optical image stabilizer, respectively. In Step S 502 , based on the first reference magnification (Z 1 ), the second reference magnification (Z 2 ), the first reference gain value (K 1 ), the second reference gain value (K 2 ), and the current magnification (ZC), the controller  114  calculates the current gain value (GC) corresponding to the current magnification (ZC) by interpolation. The first reference magnification (Z 1 ) is the minimum magnification of the image processing equipment and the second reference magnification (Z 2 ) is the maximum magnification of the image processing equipment. 
     In Step S 504 , based on the minimum magnification, the maximum magnification, the first reference gain value (K 1 ), the second reference gain value (K 2 ), and multiple additional current magnifications (ZC), the controller  114  calculates multiple additional current gain values (GC) corresponding to each of the multiple additional current magnifications (ZC) by interpolation. In Step S 506 , the controller  114  establishes a look-up table with the current magnifications (ZC) and corresponding current gain values (GC), so that when the image processing equipment is adjusted to a current magnification (ZC), a current gain (GC) corresponding to the current magnification (ZC) is used to compensate the optical image stabilizer  102 . The method then goes back to Step S 312 . 
     In the third embodiment shown in  FIG. 3D , Step S 600  is performed after Step S 308 . The first register  112  stores a first reference magnification (Z 1 ), a second reference magnification (Z 2 ), and a third reference magnification (Z 3 ) of the image processing equipment. The first reference magnification (Z 1 ), the second reference magnification (Z 2 ), and the third reference magnification (Z 3 ) are corresponding to a first reference gain value (K 1 ), a second reference gain value (K 2 ), and a third reference gain value (K 3 ) of the optical image stabilizer, respectively. The first reference magnification (Z 1 ) can be, for example, the minimum magnification of the image processing equipment and the third reference magnification (Z 3 ) can be for example the maximum magnification of the image processing equipment. 
     In Step S 602 , the controller  114  determines whether the current magnification (ZC) is between the first reference magnification (Z 1 ) and the third reference magnification (Z 3 ) or between the second reference magnification (Z 2 ) and the third reference magnification (Z 3 ). In Step S 602   a , when the current magnification (ZC) is between the first reference magnification (Z 1 ) and the third reference magnification (Z 3 ), the controller  114 , based on the first reference magnification (Z 1 ), the third reference magnification (Z 3 ), the first reference gain value (K 1 ), the third reference gain value (K 3 ), and the current magnification (ZC), calculates the current gain values (GC) corresponding to the current magnifications (ZC) by interpolation. And then the method goes back to Step S 312 . In Step S 602   b , when the current magnification (ZC) is between the second reference magnification (Z 2 ) and the third reference magnification (Z 3 ), the controller  114 , based on the second reference magnification (Z 2 ), the third reference magnification (Z 3 ), the second reference gain value (K 2 ), the third reference gain value (K 3 ), and the current magnification (ZC), calculates the current gain values (GC) corresponding to the current magnifications (ZC) by interpolation. And then the method goes back to Step S 312 . 
     Based on the above, for employing the controller  114  and the second register  116  of the gain calibration device  100 , during gain calibration, the present invention uses focal length and gain value of one magnification to quickly calculate a gain value of another magnification by interpolation, or uses one magnification or a number of different ranges of magnifications to accurately calculate a gain value of another magnification. The present invention can calibrate gain value of each magnification and use a calculated gain to compensate gain of the optical image stabilizer  102  instead of using a fixed gain value. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.