Error Analysis Of Motion Image Measurment Method

Image measurment and analysis is an usual measurement method inbiomechanics resarch. We can find the interpretation of human body’s movementrules primarily relying on the results of this kind of measurement. But imagemeasurment can also result false information and twist to the phenomenon of the bodymovements even lead to error messages and conclusion. To obtain reliablemeasurement results, we must study the size, relation and nature of the measurmenterrors, moreover, we must find some methods for errors reduction.In the1970s and1980s, the image measurement method has been widely used insports science research, meanwhile, a mount of literature and studys on the measuringerrors of this method has arised. But these findings were just fragmented and onlyconcentrate in some areas of specific problems without systematicness.Therefore, it is necessary to analysis the measurement errors in sports film andvideo, give a comprehensive inspection for the impact factors, the nature andreduction of errors. Thus, the researchers should carry on further studys on the size oferrors, avoid errors and use this method for scientific research serve correctly andeffectively for the purpose of the sports research.By constructing different capture conditions, thie study test the size of errors fortwo-dimentional and three-dimentional image measurment. The results are as follows:(1)In the mid of3/5of the view area, the distortion error of lens is small. In twodimentional analysis, there is no obvious linear relationship between camera distanceand measurement errors.(2)In three dimentional measurment, the precision is greatlyinfluenced by the camera position, the most suitable angle of cameras’ axis is about90°.(3)In the caliberation volum, the precision of inside layer is most stable, theprecision of outside layer is the lowest. Out of the caliberation volum, as the object isfar from the framework, the amout of error have a tendency to grow.(4)From themeasurements result, with the number and time of use, the coordinate values of theframwork would appeared some deviation. The average errors of all three axis are notmore than0.01m.(5) By the software photoshop and lensdoc plug-in, we can fix thedistortion errors and out-of-plane errors in time.(6) By using image measurmentmethod for action and technical quantizing analysis, we must determine the cut offfrequency of digital filtering according to the film frequency, otherwise, it is probablelead to a low cut off frequency and filter out some useful signals or high cut offfrequency and leave too much of noise.(7)The result of ANOVA analysis has showedthat if there are multiple digitizers to digitise a same movement file, the movementvariability cannot be determined reliably.The main conclusion of this text are as follows:(1)Distortion error is the mainerror sources in two dimentional image measurment method. The distortion error inthe edge of lens is depend on the camera type. Before a motion capture process, weshould choose a small distortion and stable performance of the lens in order to avoidthe distortion error which influence the measurement results.(2) In three-dimensional capturing, the location of camera can not affect the measurement accuracy whichperpendicular to the ground direction, and greatly influenced the accuracy of themeasurement accuracy which parallel to the baseline orientation of camera. Thehighest accuracy of measurement emerged when the camera optical axis angle of90°.(3)With the help of the graphics and image processing technology and processingsoftware, we can get some certain error correction. By the experiment test, it can beproved that this technique can improve the accuracy of measurement.(4) The digitizeerror is the major error source in the analysis. Because of the different personneljudgment on joint points location, the movement variability cannot be determinedreliably, so that the analytic results of reliability is greatly reduced.