眼球光心标定与距离修正的3维注视点估计

3D gaze estimation using eyeball optical center calibration and distance correction

目的在基于双目视线相交方法进行3维注视点估计的过程中,眼球光心3维坐标手工测量存在较大误差,且3维注视点估计结果在深度距离方向偏差较大。为此,提出了眼球光心标定与距离修正的方案对3维注视点估计模型进行改进。方法首先,通过图像处理算法获取左右眼的PCCR (pupil center cornea reflection)矢量信息,并使用二阶多项式映射函数得到左、右眼的2维平面注视点;其次,通过眼球光心标定方法获取眼球光心的3维坐标,避免手工测量方法引入的误差;然后,结合平面注视点得到左、右眼的视线方向,计算视线交点得到初步的3维注视点;最后,针对结果在深度距离方向抖动较大的问题,使用深度方向数据滤波与Z平面截取修正法对3维注视点结果进行修正处理。结果选择两个不同大小的空间测试,实验结果表明该方法在3050 cm的工作130 cm的工作距离内,角度偏差1. 0°,距离偏差117. 4 mm。与其他的3维注视点估计方法相比较,在同样的测试空间条件下,角度偏差和距离偏差均显著减小。结论提出的眼球光心标定方法可以方便准确地获取眼球光心的3维坐标,避免手工测量方法带来的误差,对角度偏差的减小效果显著。提出的深度方向数据滤波与Z平面截取修正法可以有效抑制数据结果的抖动,对距离偏差的减小效果显著。

Objective Gaze estimation can be divided into 2 D and 3 D gaze estimation.The 2 D gaze estimation based on polynomial mapping uses only single-eye pupil center cornea reflection(PCCR)vector information to calculate the 2 D(x,y)point of regard(POG)in a plane.The 3 D gaze estimation based on binocular lines of sight intersection needs to use the PCCR vector information of both eyes and the 3 D coordinate of the left and right eyeball optical centers(the point at which eye sight is emitted)to calculate 3 D(x,y,z)POG in a 3 D space.In the process of 3 D gaze estimation,the measurement error exists as a result of manual measurement of the 3 D coordinates of the eyeball optical center and the large deviation of the 3 D gaze estimation results in the direction of depth.On the basis of the traditional binocular lines of the sight intersection method for 3 D gaze estimation,we propose two primary improvements.We use a calibration method to obtain the 3 D coordinates of the eyeball optical center to replace manual measurement.Then,we use data filtering in-depth direction and Z-plane intercepting correction method to correct the 3 D gaze estimation results.Method First,the subject gazes at nine marked points on a calibration plane,which is at the first distance away from human eyes,and an infrared camera in front of the subject is used to capture eye images.The image processing algorithm can obtain the PCCR vector information of both eyes.The mapping functions of both eyes on the first plane can be solved according to the second-order polynomial mapping principle between the PCCR vector and the plane marked points.Second,with the calibration plane moved to a second distance,the subject gazes at the nine marked points again.With the use of the mapping functions of both eyes,the 2 D POG of both eyes at the first calibrated distance can be calculated,and the nine marked points at the second distance to the left and right 2 D POG at the first calibrated distance can be connected.Multiple lines will intersect at two points,and calculating these two equivalent intersection points obtains the calibration result of the 3 D coordinates of the eyeball optical center.Third,3 D gaze estimation can be performed.With the left and right planar 2 D POG combined with the 3 D coordinates of the eyeball optical center and with the establishment of an appropriate space coordinate system(taking the calibration plane as the X and Y plane and taking the depth of the distance as the Z axis),the lines of sight of both eyes can be calculated.According to the principle of human binocular vision,both eyes’lines of sight will intersect at one point in space,and calculating the intersection point can obtain the rough 3 D POG.The binocular vision lines are generally disjoint due to calculation and measurement errors.Thus,the midpoint of the common perpendicular should be chosen as the intersection.Finally,for the larger jitter of the resultant in-depth direction,the proposed data filtering in-depth direction and Z-plane intercepting correction method is used to correct the rough result.In this method,the data sequence of depth distance direction(Z coordinate)is first filtered.Using the filtered distance result generates a plane that is perpendicular to the Z axis.Then,the plane intercepts the left and right lines of sight to obtain two points,and the midpoint of two points is chosen as the correction result of the other two directions(X and Y).After this filtering and correction process,a more accurate 3 D POG can be obtained.Result We use two different sizes of workspaces to test the proposed method,and the experiment result shows that in the small workspace(24×18×20 cm^3),the work distance in-depth direction is 3050 cm,the angular average error is 0.7°,and the Euclidean distance average error is 17.8 mm.By contrast,in the large workspace(60×36×80 cm^3),the work distance in-depth direction is 50130 cm,the angular average error is 1.0°,and the Euclidean distance average error is 117.4 mm.Compared with other traditional 3 D gaze estimation methods,the proposed method considerably reduces the angle and distance deviation under the same distance testing condition.Conclusion The proposed calibration method for the eyeball optical center can obtain the 3 D coordinates of the eyeball optical center conveniently and accurately.The method can avoid the eyeball optical center measurement error introduced by manual measurement and reduce the angle deviation of 3 D POG significantly.The proposed data filtering in-depth direction and Z-plane intercepting correction method can reduce the jitter of the 3 D POG result in-depth direction and can reduce the distance deviation of 3 D POG significantly.This method is of great significance for the practical application of 3 D gaze.