Display Calibration Research Articles

Analysis of Crosstalk in 3D Circularly Polarized LCDs Depending on the Vertical Viewing Location.

Crosstalk in circularly polarized (CP) liquid crystal display (LCD) with polarized glasses (passive 3D glasses) is mainly caused by two factors: 1) the polarizing system including wave retarders and 2) the vertical misalignment (VM) of light between the LC module and the patterned retarder. We show that the latter, which is highly dependent on the vertical viewing location, is a much more significant factor of crosstalk in CP LCD than the former. There are three contributions in this paper. Initially, a display model for CP LCD, which accurately characterizes VM, is proposed. A novel display calibration method for the VM characterization that only requires pictures of the screen taken at four viewing locations. In addition, we prove that the VM-based crosstalk cannot be efficiently reduced by either preprocessing the input images or optimizing the polarizing system. Furthermore, we derive the analytic solution for the viewing zone, where the entire screen does not have the VM-based crosstalk.

A Robust Camera-Based Method for Optical Distortion Calibration of Head-Mounted Displays

One of the problems in using HMDs is that the virtual images shown through the HMDs are usually warped due to their optical distortions. In order to correctly compensate the optical distortions through a predistortion technique, accurate values of the distortion parameters are required. Although several distortion calibration methods have been developed in prior work, these methods have some limitations. In this paper, we propose a method for accurately estimating the optical distortion parameters of both immersive and (optical) see-through HMDs, without the limitations. The proposed method is based on photogrammetry and considers not only the radial distortion but also the tangential distortion. Its effectiveness, including the effects of different coefficient orders of radial and tangential distortions, are evaluated through an experiment conducted with two different HMDs, an optical see-through head-mounted projection display (HMPD) and a commercially available immersive HMD. According to the experimental results, the proposed method showed significantly lower reprojection and line-fitting errors than a previous method proposed by Owen , and the radial distortion coefficients estimated by the proposed method were significantly more accurate than the nominal values obtained from the HMD optics prescription. In addition, when both the radial and tangential distortions were considered, the proposed method was significantly more effective than when only the radial distortion was considered. We also discuss an OpenCV-based simple implementation of a distortion correction method.

Light-Field Correction for Spatial Calibration of Optical See-Through Head-Mounted Displays.

A critical requirement for AR applications with Optical See-Through Head-Mounted Displays (OST-HMD) is to project 3D information correctly into the current viewpoint of the user - more particularly, according to the user's eye position. Recently-proposed interaction-free calibration methods [16], [17] automatically estimate this projection by tracking the user's eye position, thereby freeing users from tedious manual calibrations. However, the method is still prone to contain systematic calibration errors. Such errors stem from eye-/HMD-related factors and are not represented in the conventional eye-HMD model used for HMD calibration. This paper investigates one of these factors - the fact that optical elements of OST-HMDs distort incoming world-light rays before they reach the eye, just as corrective glasses do. Any OST-HMD requires an optical element to display a virtual screen. Each such optical element has different distortions. Since users see a distorted world through the element, ignoring this distortion degenerates the projection quality. We propose a light-field correction method, based on a machine learning technique, which compensates the world-scene distortion caused by OST-HMD optics. We demonstrate that our method reduces the systematic error and significantly increases the calibration accuracy of the interaction-free calibration.

26.4: Display Color Error in the Medical Digital Image Workflow

AbstractThe color error produced by mobile and desktop displays is evaluated and compared relative to other error sources in the medical photography workflow. Several display calibration methods were also investigated for their effectiveness in reducing the initial color errors.

Paper No 14.1: Imaging Colorimeter for Color Calibration of Phone and Tablet Displays

AbstractIn spite of their very high color gamut, new small and medium size OLED displays are not perfect and require additional calibration to improve their performances. This is not surprising since OLED technology can suffer from homogeneity problems and small changes of emissive properties within the same display or from on display to the other. These calibrations need to be based on specific color measurements that must be very accurate and short. This specific problem is addressed in the proposed paper.

LED大屏幕显示校正系数配置系统

To effectively write and read the calibration coefficients used in LED panel display control system,a display calibration coefficient configuration system based on USB interface and FPGA was developed.Firstly,the serial flash and its application in LED display systems were introduced.Next,an electrical circuit is built,including a FPGA chip and a USB peripheral controller chip.Finally several programs were developed,including a USB firmware,a PC user program and a configuration program for the FPGA.Experiments show that the calibration coefficients can be correctly written and read with this system.Each sector of the flash can be erased in 0.6 s.The data can be written in 2.3 Mbit/s and read in nearly 30 Mbit/s.This system is easy to use,and it can take an important role in the calibration coefficients operation of the LED panel display control system.

Geometric Calibration of Head-Mounted Displays and its Effects on Distance Estimation

Head-mounted displays (HMDs) allow users to observe virtual environments (VEs) from an egocentric perspective. However, several experiments have provided evidence that egocentric distances are perceived as compressed in VEs relative to the real world. Recent experiments suggest that the virtual view frustum set for rendering the VE has an essential impact on the user's estimation of distances. In this article we analyze if distance estimation can be improved by calibrating the view frustum for a given HMD and user. Unfortunately, in an immersive virtual reality (VR) environment, a full per user calibration is not trivial and manual per user adjustment often leads to mini- or magnification of the scene. Therefore, we propose a novel per user calibration approach with optical see-through displays commonly used in augmented reality (AR). This calibration takes advantage of a geometric scheme based on 2D point - 3D line correspondences, which can be used intuitively by inexperienced users and requires less than a minute to complete. The required user interaction is based on taking aim at a distant target marker with a close marker, which ensures non-planar measurements covering a large area of the interaction space while also reducing the number of required measurements to five. We found the tendency that a calibrated view frustum reduced the average distance underestimation of users in an immersive VR environment, but even the correctly calibrated view frustum could not entirely compensate for the distance underestimation effects.

Perceptual assessment of laser‐speckle contrast

Abstract— A procedure is described for perceptually assessing the effects of laser speckle on target discrimination in the context of developing a laser‐display measurement standard. The perceptual approach avoids the difficulties inherent in assessing speckle contrast photometrically. Size thresholds for triangular test stimuli were obtained using an orientation discrimination task. Data were obtained for both a laser display and an LCD monitor using both a method of constant stimuli and a QUEST procedure. The identification threshold was 29% higher for the laser display. Given that the measured spatial resolutions of the displays were similar, the difference in threshold was attributed to the effects of laser speckle. Laser‐speckle size was also estimated as part of the display calibration. For a chosen camera f‐number, speckle‐size data are necessary to determine the sensor pixel density required to photometrically estimate speckle contrast, and they may be useful for comparison with the data obtained using the perceptual procedure described here. Mean speckle size was estimated by scaling and normalizing the laser‐speckle luminance and then determining the width of the associated autocorrelation function. It is proposed that a laser‐display standard be developed based in part upon a comparison of task performance on the laser display to be evaluated and on a standard display.

An fully automatic technique for Head Mounted Display calibration

An fully automatic technique for Head Mounted Display calibration

17.3: Visual Calibration of Displays for Accurate Contrast Reproduction

AbstractWe developed a visual calibration method (free of instruments) to characterize color display response, and demonstrate its capability to produce wide dynamic range achromatic display accurately as needed for measuring contrast sensitivity. We performed calibration and verification on both CRT and LCD monitors, and report differences between them.

Automated Fast and Accurate Display Calibration Using ADT Compensated LCD for Mobile Phone

Gamma correction is an essential function and is time consuming task in every display device such as CRT and LCD. And gray scale CCT reproduction in most LCD are quite different from those of standard CRT. An automated fast and accurate display adjusment method and system for gamma correction and for constant gray scale CCT calibration of mobile phone LCD is presented in this paper. We develop the test pattern disply and register control program in mobile phone and devleop automatic measure program in computer using spectroradimeter. The proposed system is maintain given gamma values and CCT values accuratly. In addition, This system is possible to fast mobile phone LCD adjusment within one hour.

In-field evaluation of the modulation transfer function and the signal-to-noise ratio of electronic-display devices

— This paper describes a charged-coupled device (CCD) camera, which was developed for in-field evaluation of the image quality of electronic-display devices [such as cathode-ray tubes (CRTs) and liquid-crystal displays (LCDs)] used for medical applications. Contrary to traditional cameras for display-image-quality evaluation, this CCD camera does not require a sophisticated x-y-z translation stage for mounting and adjustment. Instead, it is handheld and pressed by gentle pressure against the display screen. It is controlled by a software package which was originally developed for display calibration according to the DICOM 14 gray-scale standard display function (GSDF). This software package controls the camera gain when measurements are made at different display luminance, display test patterns, performs image analysis and displays the results of the measurements and calculations. The work concentrated on the measurement of modulation transfer function (MTF) and of signal-to-noise ratio (SNR) per display pixel. The MTF is derived from the Fourier transform of the line spread function (LSF). The single-display-pixel SNR is derived from the integration of the noise power spectrum (NPS) of a camera image taken of a display with a uniform luminance. It is demonstrated that the device can produce repeatable results in terms of MTF and SNR. MTFs were measured on three monochrome CRTs and five monochrome LCDs in order to study repeatability and similar quantities. The MTF was measured on a 5-Mpixel LCD yielding values that lie within 3.5% of the average MTF at the Nyquist frequency and 4.0% of the maximum total sharpness (∫ MTF2 df). The MTF was also measured on a 9-Mpixel LCD, yielding values that lie within 9.0% of the average MTF at the Nyquist frequency and 8.0% of the maximum total sharpness. The SNR was measured eight times on a 3-Mpixel monochrome LCD at nine digital driving levels (DDLs). At a DDL of 185, the mean SNR was 15.694 and the standard deviation (Stdv) was 0.587. At a DDL of 65, the mean SNR was 5.675 and Stdv was 0.120.

In-field evaluation of the image quality of electronic display devices

This paper describes a CCD camera, which was developed for in-field evaluation of the image quality of electronic display devices like Cathode Ray Tube displays (CRTs) and Liquid Crystal displays (LCDs). Contrary to traditional CCD cameras used for image quality evaluation, this camera does not require a sophisticated x– y– z translation stage for mounting and adjustment. Instead it is handheld and pressed by gentle pressure against the display. It is controlled by a software package which was originally developed for the display calibration according to the DICOM 14 GSDF (Grayscale Standard Display Function). This software package controls the camera gain when measurements are made at different display luminance, displays test patterns, performs image analysis and displays the result of the measurements and calculations. Initial work concentrated on the measurement of the modulation transfer function (MTF) of a CRT derived from the line spread function. The obtained MTF deviates only minimally from those obtained with a high performance CCD camera on the same CRT.

LCDs versus CRTs-color-calibration and gamut considerations

This paper presents a comparative evaluation of liquid-crystal displays (LCDs) and cathode-ray tube (CRT) displays from a color-rendition and color-calibration perspective. Common display calibration models and assumptions are reviewed and their applicability to LCDs and CRTs is evaluated through an experimental study. The displays are compared with respect to the color-calibration accuracy, ease of calibration, and achievable color gamut. The offset, matrix, and tone-response correction model commonly employed for CRT color calibration is also suitable for color calibration of LCDs for most applications, though the calibration error for LCDs is higher For the prototype LCDs used in the experimental study, large color variations significantly above the calibration accuracy are observed with changes in viewing angle. Under typical viewing conditions, LCDs provide a significantly larger color gamut than CRTs primarily due to their higher luminances.

ディスプレイ Ａｓｉａ Ｄｉｓｐｌａｙ／ＩＤＷ’０１関連 チャネル間相互作用を考慮した液晶ディスプレイの色再現特性のキャリブレーション

We describe a display calibration model that is suitable for liquid-crystal displays (LCDs). In conventional display calibration models, the spectral radiance of light emitted from the display is estimated using the data measured for each primary color based on the assumption of RGB channel additivity, however, this assumption does not hold for LCDs. With only a few measurements of the spectral radiance or tristimulus values, the proposed model accurately approximates the colorimetric characteristics of the display. To evaluate the effectiveness of the model, we used it to measure the RGB primary colors, the CMYK secondary and the tertiary colors. The colors were analyzed based on principal component analysis to identify the effect of channel interaction. The proposed model was found to be more effective than conventional models for the colorimetry of LCDs.