Effects of microlens array orientation errors on plenoptic imaging of flame radiative properties and uncertainty analysis

Plenoptic imaging(PI)systems can flexibly record both spatial and angular information on flame radiation,enabling volumetric reconstruction of complex flames.The accuracy and efficiency of the reconstruction are significantly affected by the orientation parameters of the microlens array(MLA)in the system.To investigate the influence of potential parameter errors on flame light fields,we establish a typical orientation error model and employ ray-splitting-based Monte Carlo method to simulate the entire and sectioned PI for the three-dimensional flame under four error conditions,in which different radiative properties of flame(extinction coefficient,scattering albedo,and scattering phase function)are considered.Through the proposed uncertainty evaluation scheme,the flame image characteristics,intensity,structure deviations,and their local distribution for four error types are analyzed.The results show that the extinction coefficient and the MLA error type determine the flame PI uncertainty features,while the scattering properties only change the deviation levels.The major impact of the extinction coefficient on the transfer and accumulation of uncertainty in flame-sectioned PI is also revealed.

Three-dimensional temperature reconstruction of diffusion flame from the light-field convolution imaging by the focused plenoptic camera

The plenoptic imaging technique provides a promising approach to the non-invasive three-dimensional measurement, especially for the high-temperature combustion diagnosis. We establish a light-field convolution imaging model for diffusion flame in this work, considering the radiation transfer process inside the diffusion flame and the light transfer process inside the focused plenoptic camera together. The radiation transfer process is described by the radiation transfer equation and solved by the generalized source multi-flux method. Wave optics theory is adopted to describe the light transfer process, combining Fresnel diffraction and the phase conversion of the lens. The flame light-field image is obtained by the light-field convolution imaging model and adopted as the measurement signal to reconstruct three-dimensional temperature field. The inverse problem of temperature reconstruction is solved by the least square QR decomposition method. The simulative temperature reconstruction work is conducted, including the inverse analysis, the uncertainty analysis, and the measurement noise influence. All the results show that the proposed measurement method is available to reconstruct three-dimensional temperature with satisfactory accuracy and acceptable uncertainty. Both symmetric and asymmetric distributed temperature fields are investigated, and the reconstructed results prove the validity and universality of the measurement method.

Experimental assessment of a 3-D plenoptic endoscopic imaging system

All endoscopic imaging system using a plenoptic technique to reconstruct 3-D information is demonstrated and analyzed in this Letter. The proposed setup integrates a clinical surgical endoscope with a plenoptic camera to achieve a depth accuracy error of about 1 mm and a precision error of about 2 mm, within a 25 mm×25 mm field of view, operating at 11 frames per second.