Patent Publication Number: US-8111292-B2

Title: Method and apparatus for stably correcting handshake in camera panning situation

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2007-0100346, filed on Oct. 5, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image capturing apparatus such as a camera or camcorder, and more particularly, to a method and apparatus for stably correcting handshake that occurs during a camera panning situation. 
     2. Description of the Related Art 
     While image capturing is performed using an image capturing apparatus such as a camera or camcorder, the image capturing is mostly performed by a user holding the image capturing apparatus in his/her hands, without using a tripod. At this point, shaking is generated in the shooting apparatus due to movement of the hands holding the image capturing apparatus. Also, the shaking of the image capturing apparatus causes shaking of an image being captured. Therefore, it is necessary for the image capturing apparatus to automatically detect and correct handshake. 
     The handshake is unintentionally generated while image capturing is being performed by using an image capturing apparatus. Meanwhile, panning is an operation in which a user intentionally changes a shooting direction of the image capturing apparatus. Panning means horizontally moving the shooting direction of the image capturing apparatus so as to move an image displayed on a screen in a lateral direction. 
       FIG. 1A  is a graph explaining a conventional method of correcting movement caused by handshake. 
     A y-axis represents an accumulated value of movement vectors in relation to a time axis, and an x-axis represents time. Reference numeral  130  refers to an accumulated value of movement vectors, reference numeral  110  refers to a handshake section, and reference numeral  120  refers to a panning section. 
     Referring to  FIG. 1A , it appears that the accumulated value of the movement vectors, which are due to the random handshake of a user, is represented as a waveform at a constant level. However, when the user&#39;s intentional movement, that is, a situation such as panning occurs, the accumulated value of the movement vectors increases consistently. Therefore, when the accumulated value increases beyond a predetermined level, or movement in the same direction is continuously detected at a predetermined level, it is judged as panning. 
     However, the conventional method of judging panning or tilting when movement vector values successively appear in the same direction a predetermined number of times has a limitation for the case illustrated in  FIG. 1B . 
       FIG. 1B  illustrates an accumulated value of movement vectors for the case where an abnormal situation occurs during a panning mode. Reference numeral  122  refers to a section where the abnormal situation occurs during a panning operation. 
     Referring to  FIG. 1B , an image capturing apparatus does not detect a panning situation when a user&#39;s handshake occurs during a panning operation and movement is made in a direction opposite to that of the panning operation, so that it is difficult to correct the handshake. 
     SUMMARY OF THE INVENTION 
     The present invention provides a stable handshake correcting method to be used during a camera panning situation by matching a regression line model or a regression curve model with accumulated movement information in an image capturing apparatus such as a camera or camcorder. 
     According to an aspect of the present invention, there is provided a handshake correcting method including: accumulating movement information in predetermined units for a predetermined period of time; matching a regression model to the accumulated movement information to determine a situation as one of a panning mode and a handshake mode; performing switching between the handshake mode and the panning mode according to a matching factor generated by the matched regression model; and correcting handshake on the basis of a handshake correcting amount determined according to one of the handshake mode and the panning mode. 
     The performing of switching between the handshake mode and the panning mode may include: changing the panning mode to the handshake mode when a slope value predicted by the regression model is smaller than a threshold value, or correlation between an accumulated movement vector value and a coefficient of a regression line or curve is smaller than the threshold value during the panning mode; and initializing the accumulated movement vector value to control a current corrected amount. 
     The performing of switching between the handshake mode and the panning mode may include: changing the handshake mode to the panning mode when a slope value predicted by the regression model is greater than a threshold value during the handshake mode; and initializing the accumulated movement vector value to control a current corrected amount. 
     According to another aspect of the present invention, there is provided a handshake correcting apparatus including: a movement predicting unit estimating movement information in predetermined units; a handshake correcting information generating unit accumulating the movement information estimated by the movement predicting unit for a predetermined period of time to match a regression model to the accumulated movement information, and extracting movement correcting information for controlling a movement correcting amount depending on whether an inflection point is detected according to coefficient information of the regression model; and a movement correcting unit correcting handshake on the basis of a handshake correcting amount extracted from the handshake correcting information generating unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIGS. 1A and 1B  are graphs explaining a conventional method of correcting movement caused by handshake; 
         FIG. 2  is a block diagram of a handshake correcting apparatus according to an exemplary embodiment of the present invention; 
         FIG. 3  is a detailed view of a handshake correcting information generating unit illustrated in  FIG. 2 ; 
         FIG. 4  is a graph illustrating an accumulated entire range movement vector; 
         FIG. 5  is a graph illustrating a regression line matched with accumulated movement information; 
         FIG. 6  is a graph illustrating a regression line matched with accumulated movement information for the case where an abnormal situation occurs; and 
         FIG. 7  is a detailed flowchart of a process at an inflection point detecting unit illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
       FIG. 2  is a block diagram of a handshake correcting apparatus according to an embodiment of the present invention. 
     The handshake correcting apparatus illustrated in  FIG. 2  includes a movement predicting unit  210 , a handshake correcting information generating unit  220 , and a movement correcting unit  230 . 
     The movement predicting unit  210  divides a captured image signal into blocks or regions of predetermined units, and estimates movement vectors for the divided blocks, respectively, using a block matching algorithm. For example, the movement predicting unit  210  calculates a difference between a block of a reference frame (or a previous frame) and a block of a current frame by using time correlation between adjacent frames to estimate a movement vector for each block. Also, the movement predicting unit  210  explores global movement vectors of an image so as to correct an image where handshake has occurred, in a time direction. 
     The handshake correcting information generating unit  220  accumulates global movement vectors explored by the movement predicting unit  210  for a predetermined period of time, and matches a regression model with the accumulated global movement vectors in order to determine whether a situation is performed in a panning mode or a handshake mode. Also, the handshake correcting information generating unit  220  switches between the handshake mode and the panning mode with reference to correlation between a coefficient of the matched regression line or curve and the accumulated global movement vectors, and generates movement correcting information corresponding to the switched handshake mode or the panning mode. At this point, the movement correcting information includes a handshake correcting amount and a movement correcting command. 
     The movement correcting unit  230  performs handshake correction using the global movement vectors of the movement predicting unit  210  according to the movement correcting information generated by the handshake correcting information generating unit  220 . 
       FIG. 3  is a detailed view of the handshake correcting information generating unit  220  illustrated in  FIG. 2 . 
     A movement accumulator  310  accumulates movement information successively provided in time for a predetermined period of time to accurately discriminate between a panning situation and a handshake situation. Here, the movement information means a global movement vector of a current frame extracted by a movement estimating block or sensor. Although the movement accumulator  310  may need to accumulate global movement vectors for a long time to accurately predict handshake, the movement accumulator  310  may accumulate the global movement vectors for a short time so as to prevent a delay. 
     A buffer  320  constantly stores the accumulated global movement vectors accumulated by the movement accumulator  310 . 
     At this point, the global movement vectors stored in the buffer  320  can be represented by a graph as illustrated in  FIG. 4 . In  FIG. 4 , a y-axis represents an accumulated size for global movement vectors in relation to a time axis, an x-axis represents time, and reference numeral  403  refers to an actually accumulated global movement vector value. Referring to  FIG. 4 , an accumulation amount increases in a positive direction over time. 
     A counter  330  counts global movement vectors accumulated in the buffer  320 . 
     A regression modeler  340  matches a regression line or curve model to the global movement vectors stored in the buffer  320  when the number of accumulated global movement vectors is greater than a threshold value, and delivers a movement correcting command that uses a global movement vector not corrected by the movement correcting unit  230  when the number of accumulated global movement vectors is smaller than the threshold value. Also, the regression modeler  340  determines a panning degree by using a coefficient of the order of the matched regression line or curve. 
     Therefore, a matched regression equation representing an accumulated data pattern in the form of a first order regression line model can be given by Equation 1. In another embodiment of the present invention, the accumulated data pattern can be represented in the form of a regression line model of a high order function. 
                     Y   =       β   0     +       β   1     ⁢   x     +   ɛ0       ⁢     
     ⁢         β   1     =       ∑       (       X   i     -     X   _       )     ⁢     (       Y   i     -     Y   _       )           ∑       (       X   i     -     X   _       )     2           ,             Equation   ⁢           ⁢   1               
where Y is an observed value of an actually accumulated movement vector, β 0  is an intercept, β 1  is a slope of a matched first order regression line, x is a position in time, and ε 0  is a residual between a matched first order regression line and an actually observed movement vector. Also, X i  and Y i  are an x coordinate and a y coordinate of a straight line in a 2 dimensional (2D) coordinate system, respectively, and  X,Y  are average values of data on an x-axis and a y-axis, respectively.
 
     The matched regression line is shown in the graph illustrated in  FIG. 5 . Referring to  FIG. 5 , reference numeral  504  refers to a matched regression line. The regression line is an intentional panning component of a user in a camera movement. Reference numeral  506  refers to handshake information of the user, which is generated externally. 
     Therefore, the global movement vectors accumulated in the buffer  320  are matched with a regression line or curve by using the regression line model. However, referring to  FIG. 6 , in the case where a user&#39;s panning stops and a stop situation (section denoted by reference numeral  606 ) occurs, a regression model matched with accumulated movement vectors is expressed by a straight line  604 . Evidently, the slope of the regression line  604  illustrated in  FIG. 6  is smaller than the slope of the regression line  504  illustrated in  FIG. 5 . 
     In the case where the user&#39;s panning stops and the stop situation (section denoted by reference numeral  606 ) occurs as illustrated in  FIG. 6 , an inflection point occurs at a predetermined point of time, tx  605 , and thus, an error in the movement information is not detected. Therefore, when an abnormal situation occurs and movement vectors accumulated in the buffer  320  match with the regression line model, an error is generated. Here, the inflection point means a turning point in accumulated movement data at which a panning speed or direction drastically changes. 
     Therefore, an abnormal situation needs to be detected in order to reset the buffer  320 , and accumulate new movement information. Examples of the abnormal situation include the case where a panning operation and handshake simultaneously occur and then the panning operation stops and the handshake continues to occur during an image capturing operation performed by a user using a camera, and the case where the handshake stops and the panning operation occurs at a predetermined point during an image capturing operation performed by a user using a camera. Whether the abnormal situation occurs or not is determined by using a correlation coefficient generated in a regression model, the size of a residual, or pattern generation information of a residual. 
     An inflection point detector  350  extracts an inflection point using coefficient information of a regression model generated by the regression modeler  340 , and generates movement correcting information for controlling a movement correction amount depending on whether the inflection point exists or not. 
     Also, the inflection point detector  350  outputs a movement correcting command for compensating a movement using movement information not corrected when an inflection point is detected, and simultaneously, outputs a rest signal to the buffer  320 . Also, when the inflection point detector  350  does not detect an inflection point, it outputs a movement correcting command for compensating a movement using corrected movement information. At this point, the corrected movement information can be expressed by a movement correcting value as in Equation 2.
 
 MV   a =GMV−PV× R   2   Equation 2
 
where GMV is an global movement vector, PV is a predicted value corresponding to the slope of a regression line, R 2  is a correlation coefficient between a global movement vector value and a coefficient of a regression line. Here, R 2  is a fitting accuracy for the case where data fitting is performed on actual data by using a regression line. When the regression line is matched with accumulated global movement vector values, R 2  is inversely proportional to a handshake amount. That is, since handshake reduces when the size of panning is large, R 2  increases. On the other hand, since handshake relatively increases when the size of panning is small, R 2  reduces.
 
     Also, R 2  can be given by Equation 3 below. 
                       R   2     =       1   -       ∑     ⅇ   ⁢           ⁢     i   2           ∑       (     Yi   -     Y   _       )     2           =     1   -     RSS   TSS           ,           Equation   ⁢           ⁢   3               
where RSS (residual sum of squares) is the sum of residuals for the case where data fitting is performed on actual data by using a regression line, and TSS (total sum of squares) is a variation component of an entire dependent variable.
 
     The inflection point detector  350  extracts an inflection point. Thus, the inflection point detector  350  judges the panning mode and the handshake mode using slope information β 1  and correlation coefficient information R 2  generated by the regression modeler  340 , and switches between the handshake mode and the panning mode. 
       FIG. 7  is a detailed flowchart of a process at the inflection point detecting unit illustrated in  FIG. 3 . 
     First, the regression modeler  340  inputs the slope information β 1  and correlation coefficient information R 2 . 
     At this point, a predicted value PV corresponding to the slope β 1  of the regression line predicted at a predetermined point is compared with a threshold value TH (operation  710 ). 
     Here, when panning occurs, the slope of the regression line is large. When panning does not occur, the slope of the regression line is small. Therefore, when a predicted value PV corresponding to a relevant slope is greater than a threshold value TH set in advance, a situation is determined as the panning mode P, and otherwise, the situation is determined as the handshake mode H. 
     Subsequently, after the situation is determined as the panning mode P, a point, at which movement data that is successively input is switched from the panning mode P to the handshake mode H, is detected. 
     That is, in the case where the situation was the panning mode up to a previous frame but an input predicted value PV is smaller than a threshold value TH or the correlation coefficient R 2  is smaller than the threshold value TH, the panning mode P is switched to the handshake mode H from a corresponding point (operation  720 ). However, when the input predicted value PV is greater than the threshold value TH or the correlation coefficient R 2  is greater than the threshold value TH, the panning mode P is still maintained, and a movement correcting command for performing movement correction using corrected movement data given by Equation 2 is output. 
     At this point, when the situation is switched from the panning mode P to the handshake mode H, it is determined that there is no panning, and a reset operation for specific coefficients is performed. Therefore, a reset operation by performing mode switching initializes an accumulation value of movement vectors to control a current movement correcting amount (operation  750 ). For example, a corrected value MV a  of movement data is changed to “0”, and a count value CNT stored in the buffer is changed to “0”. 
     Also, in the case where the situation was in handshake mode up to a previous frame but an input predicted value PV is greater than a threshold value TH, the handshake mode H is switched to the panning mode P from a corresponding point of time (operation  730 ). However, when the input predicted value PV is smaller than the threshold value TH, the handshake mode H is still maintained, and a movement correcting command for performing movement correction using corrected movement data given by Equation 2 is output. 
     At this point, when the situation is switched from the handshake mode H to the panning mode P, a reset operation for specific coefficients is performed. Therefore, a reset operation by performing mode switching initializes an accumulation value of movement vectors to control a current movement correcting amount (operation  750 ). For example, a corrected value MV a  of movement data is changed to “0”, and a count value CNT stored in the buffer is changed to “0”. 
     The invention can also be embodied as computer readable codes on a computer readable recording medium or other computer readable medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. An example of other computer readable media is carrier waves (such as data transmission through the Internet). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     According to the present invention, a panning component can be predicted accurately and quickly, and a slight handshake that occurs during a panning operation can be detected by matching a regression line model or a regression curve model to movement information accumulated by an image capturing apparatus such as a camera or camcorder. Therefore, the present invention can effectively remove a handshake component that occurs during a camera panning situation. 
     While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.