Estimation of any fields of lens PSFs for image simulation

Abstract

In a mobile smartphone camera, image quality is more degraded towards the edges of an image sensor due to high CRA (Chief Ray Angle). It is critical to estimate the cause of this effect since image quality is degraded at image periphery from attenuating illuminance and broadening PSF (point spread function). In order to predict image quality from the center to the edge of the camera output, we propose a method to estimate lens PSFs at any particular image field. The method adopts Zernike polynomials to consider lens aberrations while having an arbitrary spatial sampling. Also, it employs estimating a pupil shape in accordance with an optical field. The proposed method has two steps: 1) estimation of a pupil shape and Zernike polynomial coefficients, and 2) generation of a PSF with estimated parameters. The method was experimented with a typical mobile lens to evaluate the performance of the PSF estimation at 0.0F and 0.8F. In addition, Siemens star images were generated with the estimated PSFs to compare resolutions at the center and the edge of an image. The results show that the image of the edge is worse than that of the center in terms of MTF (Modulation Transfer Function), showing the importance of assessing image quality at the edge for pre-evaluation of a mobile camera.