Motionless shape-from-focus depth measurement via high-speed axial optical scanning

Shape-from-focus depth measurement is widely used in equipment manufacturing, biomedicine, heritage conservation, engineering measurement, etc. However, the acquisition of multi-focus image sequence is not very flexible and time-consuming in conventional shape from focus. Here, a novel depth measurement from shape from focus method based on ultrafast optical axial scanning was proposed. An electronically tunable lens was used to achieve high-speed focus shift, by synchronizing a CCD with the electronically tunable lens, multi-focus image sequence can be acquired at high speed (up to 2.5 ms). The focusing area of each multi-focus image was extracted by the energy of image gradient operator. Finally, the motionless depth measurement can be achieved. A tilted marker pen was used to test the performance of the depth measurement, the results show that the depth resolution of the proposed method is measured to be-3.2 cm in a depth range of-24 cm. The feasibility of the proposed method was verified using misplaced portrait sculptures. This method will further expand the application of depth measurement from shape from focus in human-computer interaction, 3D shape measurement, and augmented reality.