Modulation transfer function measurement o the rigid endoscope by a random method

A random method is presented to measure the modulation transfer function (MTF) of the rigid endoscope, evaluating its imaging quality. The experimental setup includes a four-dimensional (4D) mobile platform, a non-full-screen liquid-crystal display (LCD), three different kinds of patterns, a nasoendoscope of 0 degrees direction of view under measurement, a complementary metal oxide semiconductor (CMOS) device, and a computer. The method is divided into three steps to complete the MTF measurement. First the geometric distortion is evaluated to determine the suitable sampling matrix (SSM) by the grid pattern. Then the illuminance inhomogeneity distribution is evaluated to obtain the illuminance compensation curve by the uniform grayscale pattern. Finally the MTFs are acquired by analyzing the spatial frequency contents of the compensated SSMs by the random patterns. By analysis and comparison, the method can improve the stability and accuracy for the MTF measurement in a simplified way. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement