Extended depth of focus as a process of pupil manipulation

Abstract

During the last few years, the understanding of pupil plane manipulation capabilities to achieve an enhanced image formation process and its theoretical limitations becomes more and more important. Particularly the increased potential of computer calculations and digital signal detection makes it possible to simulate this kind of manipulations very fast and efficient. At the same time there is the opportunity to change the optical system such, that a digital reconstruction of the image gives a higher amount of information. An analysis of the optical transfer function as an important parameter of imaging quality with special interest in extended depth of focus is presented. The performance of different pupilplane masks is illustrated in comparison with standard optical systems. This means the basic features like depth of focus, resolution and contrast were derived and the limitations are shown. The mathematical principle of extended depth of focus with pupil manipulation is described and demonstrated with exemplary calculations. Furthermore, the relation between a given optical transfer function and the matching pupil function is shown. A robust and iterative algorithm is presented to calculate a pupil mask for a desired optical transfer function.

Extended depth-of-field using sharpness transport across color channels

“…In the design of high-resolution camera modules for mobile phones, the problem of finding the best trade-off between (i) imaging resolution (number of pixels), (ii) light gathering ability (f /# and pixel size), and (iii) Extended Depth-of-Field (EDoF), can be overcome by combining the use of suitable amplitude or phase masks in the pupil plane of the lens with post-detection signal processing [5] . Traditional optical designs do not lend themselves well to digital restoration in the presence of defocus aberration because of both the regions of zero values in the imaging system's MTF (cf.…”

“…In miniature camera applications for which light gathering ability is critical, phase modulation of the pupil function offers a complementary or alternative solution for the EDoF problem [5] . By adding a non-absorbing like aspheric optical elements such as cubic-phase or cosine form-phase masks 2 , it is possible to code the received incoherent wavefront in such ways that (i) the PSF of the imaging system becomes more insensitive to misfocus, and (ii) The PSF is "shaped" 3 so that its MTF (magnitude of its Fourier transform) has no nulls in its spectrum (up to at least half Nyquist frequency), while the full-aperture area is maintained [9] .…”

Comparison between a new holographically generated complex filter and the binary phase filter for depth-of-field extension

“…2 and Fig. 4, and the HGCF for the same focal length and aperture radius at a wavelength of nm 632 = λ , which is designed to produces the same defocus given by the following defocus parameter 9 .…”

Resultados preliminares de um sistema computadorizado e estereoscópico para pupilometria in vivo

“…No entanto, ao contrário do que se pensa, sua função não é apenas controlar a luminosidade que incide na retina, mas também regular a profundidade de foco (3) . Para focalizar objetos distantes o seu diâmetro diminui, e para objetos próximos o diâmetro aumenta, de maneira involuntária, mas altamente precisa (4) , daí a importância de se estabilizar não somente a quantidade de iluminação, mas também a acomodação do cristalino para se determinar o diâmetro pupilar.…”