ISO 12233 provides a method for measuring Modulation Transfer Function (MTF) of digital input devices based on a slanted-edge method. However, the results measured by the method are greatly affected by image processing procedures, especially sharpening, and false MTF is often given. In this article, an improved slanted-edge method is proposed where an edge-preserving filter with optimal parameters is introduced to smooth the image before implementing ISO 12233 method. Particularly, three edge-preserving filters, bilateral filter, guided filter and adaptive weighted least square filter, and one general filter, Gaussian filter, are compared in mitigating the effect of sharpening algorithm on the measurement of digital camera MTF. The experimental results indicate that the effect of sharpening algorithm on the measured MTF can be effectively reduced by using an edge-preserving filter, and significantly improvement on the MTF accuracy at Nyquist frequency is achieved. Especially, the slanted-edge method based on the guided filter and the weighted least squares filter can give more real MTF for a digital camera.
Coherent optical systems face two main categories of linear impairments, chromatic dispersion (CD) and polarization mode dispersion (PMD). Both CD and PMD will create large inter-symbol interference (ISI). This paper focuses on M-quadrature amplitude modulation (QAM) signal detection directly using Echo State Networks (ESN) technique for compensating (residual CD and PMD) dispersion of coherent optical systems. The proposed approach can estimate directly the input sequence at the coherent receivers, without getting the electronic equalizer coefficients and estimating optical channel impulse response. In addition, the proposed approach can guarantee a convergence within a short data packet.
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