Image enhancement by sequential frecuency multiplexing of images obtained with non-uniform transmission pupils

I. ESTEVEZ; J. ESCALERA; A. MÁRQUEZ; C. IEMMI; M. YZUEL; J. CAMPOS

Santiago de Compostela

Congreso; ICO 23; 2014

International Comission for Optics

There are different image quality criteria to analyze the image performance of an optical system. The Point Spread Function (PSF) is commonly used to that purpose [1-2]. The Optical Transfer Function (OTF) and the Modulation Transfer Function are used to analyze the frequency transmission of an optical system [3-5]. Pupil filters have been widely used to improve some characteristics of the response of optical systems [6-9]. For instance, apodizing filters can reduce secondary maxima on the PSF [10-11]. Different types of superresolving filters have been used to sharpen the principal maximum of the PSF, increasing the resolving power [12-13].In the last years many papers deal with the fast-developing area of computational photography where a combination of imaging techniques and efficient image processing algorithms are done to generate a super imaging system. Three main implementations of the computational photography philosophy have been intensively investigated and demonstrated: (i) multiple aperture, (ii) light field photography, and (iii) multiexposure [14-16].In this paper we show that the OTF produced by some apodizing filters is better than clear pupil for low frequencies, though the transmission of high frequencies is worst. On the contrary, we also show that some superresolving filters transmit better the high frequencies than the clear pupil, but with bad behavior in the low frequency spectrum. So, we propose to capture an image obtained with the low pass filter (apodizing filter) and another taken with the high pass filter (superresolving filter). Then, we will combine the low and high frequency content from both images through a post-processing. We show that we can create an enhanced image better than the obtained with the clear aperture. Special care has to be taken in how the frequency multiplexing is done, to avoid unwanted effects on the global response. To check the effect of this process in an image, bar tests (sinusoidal tests) with different frequency content are used.