A remapping algorithm based on weighted coefficients for SAPIV

Synthetic aperture particle image velocimetry (SAPIV) is a flow field diagnostic technique that provides instantaneous velocimetry information non-intrusively. In SAPIV, particle scattering images are captured from different cameras with camera array configuration. To acquire refocusing images, images are remapped and accumulated in pre-designed remapping planes. During the refocused images, particles that lie in the remapped plane are aligned and appear sharp, whereas particles off this surface are blurred due to parallax between the cameras. During the remapping process, captured images are back-projected to different remapped planes of different depth z within the volume. The projected images from different cameras, which are called remapped images, are merged to generate refocused images at different depth z. We developed a remap method based on the weight coefficient to improve the quality of the reconstructed velocity field. The images captured from the cameras are remapped into different remapped planes by use of homography matrix. The corresponding pixels of the remapped images in the same remapped plane are first added and averaged. The corresponding pixels of the remapped images in the same remapped plane are multiplied and the obtained intensity values act as the weight coefficients of the intensity in the added refocused image stacks. The unfocused speckles can be restrained to a great degree, and the focused particles are retained in the added refocused image stacks. A 16-camera array and a vortex ring field at two adjacent frames are simulated to evaluate the performance of our proposed method. In the simulation, a vortex ring can be clearly seen. An experimental system consisting of 16 cameras was also used to show the capability of our improved remap method. The results show that the proposed method can effectively restrain the unfocused speckles and reconstruct the velocity field in the flow field.