数字全息中利用图像拼接测量大物体的三维形貌

为扩大数字全息的测量视场,使数字全息可以应用于大物体三维形貌的测量,利用菲涅耳离轴数字全息,让照明光依次照明物体的各个区域并分别记录全息图,利用精密电控旋转台精确控制参考光的入射角以保证每次记录时物参角不变,通过参考光入射角的变化量确定物体不同被照明区域之间的位置关系,对获得的物体去包裹的相位图进行拼接,进而得到整个物体的三维形貌.利用该方法测量了大小为11 cm×19 cm的石膏嘴的三维形貌,图像拼接的绝对拼接误差远小于1.14 mm,高度测量误差约为0.5 mm,实验结果说明这种测量方法能够有效地扩大数字全息测量物体三维形貌的视场并且具有和横向分辨率相当的拼接精度.

Three-Dimensional Surface Shape Measurement of Big Objects by Image Splicing in Digital Holography

To enlarge the field-of-view of digital holographic surface measurement, so that digital holography can be applied in three-dimensional(3-D) surface measurement of large objects,based on Fresnel off axis digital holography, different part of the object is illuminated singly and their holograms are recorded respectively. The object-reference angle remains the same for each recording by precisely controlling the incident angle of the reference wave using an electronically controlled turntable. The position of the illuminated part can be obtained from the change of the incident angle of reference wave. The unwrapped phase maps are spliced to obtain the 3-D surface shape of the whole object. The 3-D surface shape of a 11 cm×19 cm plaster mouth model is measured using this method. The absolute splicing error is no more than 1.14 mm and the surface height error is about 0.5 mm. It is proved that this method is very effective in enlarging the field-of-view of digital holographic 3-D surface shape measurement and its splicing precision is as high as the lateral resolution of digital holography.