Novel NPS measurement method for medical liquid crystal display using periodic components subtraction technique
Katsuhiro Ichikawa, Yoshie Kodera, Akiko Horii · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2006
A novel noise power spectrum (NPS) measurement method for medical liquid crystal display (LCD) was developed. A uniform image displayed on an LCD was imaged with a high-resolution single-lens reflex type digital camera (D70, Nikon) equipped with a close-up lens. In order to avoid significant errors (frequency leakages) caused by strong periodic components of the pixel structures, noise profile data was processed by periodic components subtraction, and NPS was calculated from the processed profile with fast Fourie transformation (FFT). Horizontal NPS at the center of display area was measured up to the 10 times of Nyquist frequency. Actual measurements were performed with various models of monochrome two million and three million pixel LCDs to investigate difference of conventional method and our proposed method. Resultant NPS obtained from the conventional method with simple FFT included significant errors over the whole frequency ranges. In contrast, our proposed method could compensate most of those errors. Resultant NPS of our method indicated clearly the difference of noise property between three displays we measured, which corresponded to the visual evaluation for them. In conclusion, our method is very useful for evaluation of noise properties of medical LCD due to the good accuracy and reproducibility.