Analysis method of noise power spectrum for medical monochrome liquid crystal displays

Abstract

We investigated methods of analyzing the noise power spectrum (NPS) measurement for medical liquid crystal displays (LCDs). Uniform images displayed on the LCDs were imaged with a high-performance digital camera equipped with a close-up lens, and then the NPSs were calculated from the image data by means of several analysis methods. In a method using the 2D fast Fourier transform (FFT) with a 256 x 256 pixels data segment (basic method), we examined the efficacy of a background trend correction (BTC) and a Hanning windowing process used for reducing the spectral estimation errors in the Fourier analysis. To improve the frequency resolution of the basic method, we examined two 2D FFT methods by using 512 x 512 and 1024 x 1024 pixel segments. In addition, we studied a 1D FFT method with 1024-point 1D noise profiles (1D method). In these three methods, the BTC by a second-order polynomial fit and Hanning windowing were commonly applied. A 3-mega-pixel (MP) and a 5-MP monochrome LCD were employed for evaluating the respective methods. Also, a prototype 5-MP LCD equipped with a new anti-reflection surface-coated panel was compared with the conventional 5-MP LCD. The Hanning windowing process was indispensable for avoiding the spectral leakage errors caused by the pixel structures of the LCD. Sufficient frequency resolution was obtained by the 2D FFT method with the 1024 x 1024 pixels segments and the 1D method. The method which provided the most reliable NPSs was the 1D method, with which the BTC was achieved successfully.

Overall noise characteristics of reduced images on liquid crystal display and advantages of independent subpixel driving technology

“…Pre- viously, it was confirmed that the camera had good linearity of the camera-pixel value to display luminance. 3 Since the NPS of the camera is about 10 2 times lower than the display-NPS level, the camera noise is negligible in display-noise measurements. 3 The displayed bar-pattern images in the horizontal and vertical directions were captured and consequently the MTFs in the two directions were calculated.…”

“…3 Since the NPS of the camera is about 10 2 times lower than the display-NPS level, the camera noise is negligible in display-noise measurements. 3 The displayed bar-pattern images in the horizontal and vertical directions were captured and consequently the MTFs in the two directions were calculated. In the vertical direction, we measured the MTF of the 3-MP LCD without ISD and of the 9-MP LCD with ISD.…”

“…Several researchers have already investigated and reported inherent image characteristics of various LCDs as modulation transfer function (MTF) and noise power spectrum (NPS), which are attributed to the matrix size, pixel-structure shape, aperture ratio, screen filter, etc. [1][2][3][4][5][6] Fur-ther, Bacher et al reported the observer-performance results of image characteristics on LCDs by using window setting and magnification. 7 In this study, we performed theoretical analyses for inherent image characteristics as well as the overall noise characteristics of displayed images on a LCD for varying magnifications.…”

Visual evaluation and usefulness of medical high-resolution liquid-crystal displays with use of independent sub-pixel driving technology

“…On resolution measurement, test pattern images for the bar-pattern method were displayed on the monitor and photographed with a single-lens reflex digital camera (D70, Nikon, Tokyo, Japan) [4]. The MTF was calculated from the raw data from the charge-coupled device (CCD) by use of an analytical system (NS-2002, S.S. Techno, Nagoya, Japan).…”

Comparison of viewing angle and observer performances in different types of liquid-crystal display monitors

“…LCD monitors have a number of advantages compared to CRT monitors, such as a high maximum luminance, low reflection of ambient light, and no warping in the entire image [3]. On the other hand, LCD monitors have potential disadvantages, such as noise of the pixel structure [4,5], limited temporal resolution, limited minimum luminance, and varied viewing angle performance [6,7]. However, the effects of these potential disadvantages on image readings are not well known.…”