Improvement of Gray Scale CCT for Mobile Phone LCD

Display Technologies III, 2000

Color LCD (Liquid Crystal Display) has been widely used for personal computers (PC) and video monitors because of its light weight, small volume, low power consumption and so on. Color reproductions for LCD panels are different from that of CRT (Cathode Ray Tube) display. This study describes the difference of color gamuts in different luminance level and the accuracy of color between CRT and LCD. In the present study, the reproduction color gamuts on the chromaticity diagram are measured in three types of displays, including two CRT types (BARCO Reference Calibrator Plus and ViewSonic PT775) and one LCD type (NEC MultiSync LCD 200). In the experiment, the tristimulus values XYZ for the combinations of three primary colors R(red), G(green), B(blue) were measured by varying the input digital levels. The digital levels which varied from 0 to 255 in every primary color were equally divided into 17 stages, including 0 and 255, and thus the tristimulus values of 4913 colors at each display were measures. Size and shape of color gamuts varied with the luminance, sampling distribution and color difference of LCD and CRT will be discussed. The higher the value of Y, the smaller the area of the color gamut, no matter which display type performed. The area of the color gamut of LCD is smaller than that of CRT in most levels of luminance. This paper discovered that some special patterns exist in color gamut diagrams. Final, relationships among patterns have been clarified for characterizing the color gamuts of displays.

2018

The main purpose of this research is to study the colour characterisation of digital display systems. Three distinct models for characterisation (GOG, PLCC and PLVC) are evaluated and compared and for two of these models (GOG and PLCC) two different sets of linearisation samples (either colour-ramps or grey-ramp samples) are used to perform the linearisation. To evaluate these models’ colorimetric measurements are made for 20 different display devices and colour characterization performance is reported as the main measure. Characterisation performance is calculated using several sets of samples including the widely used Macbeth ColorChecker chart and two new charts called Chart4 and Matlab60 (one of which was based on a method previously published by Cheung and Westland and another was based on a new method). A key aspect of this work is that all 256 levels of intensity were measured for the colour-ramps and for the grey-ramp linearisation samples for each of the 20 displays to allo...

2006

This research aimed to evaluate performance of two characterization methods: 3D LUT and S-curve model, for LCD characterization. In the experiment, the colorimetric values were measured with a spectroradiometer in a dark room. Before characterization, the characteristics of LCD monitor were tested, which were spectral characteristics, channel independence, chromaticity constancy, spatial independence, spatial uniformity, temporal stability. It was found that this LCD had good performance for all properties. In the characterization process, two training sets were used: one had 729 sample data for creating 3D LUT and the other had a 36-step neutral ramp for creating the S-curve model. The performance of the characterization models was tested using a test set, which contained 200 random colors. The average color difference ( [delta]E*ab) between measured colors and predicted colors from 3D LUT was 1.8. The average color difference ( [delta]E*ab) between measured colors and predicted co...

Color Research & Application, 2008

This work proposes a study of the Piecewise Linear assuming Variation in Chromaticity (PLVC) display color characterization model. This model has not been widely used as the improved accuracy compared with the more common PLCC (Piecewise Linear assuming Chromaticity Constancy) model is not significant for CRT (Cathode Ray Tube) display technology, and it requires more computing power than this model. With today's computers, computational complexity is less of a problem, and today's display technologies show a different colorimetric behavior than CRTs. The main contribution of this work is to generalize the PLVC model to multiprimary displays and to provide extensive experimental results and analysis for today's display technologies. We confirm and extend the results found in the literature and compare this model with classical PLCC and Gain-Offset-Gamma-Offset models. We show that using this model is highly beneficial for Liquid Crystal Displays, reducing the average error about a third for the two tested LCD projectors compared with a black corrected PLCC model, from 3.93 and 1.78 to respectively 1.41 and 0.54 DE Ã ab units.

Acta Graphica, 2017

The ciecam02 colour appearance model was developed to allow prediction of accurate colour appearance under various viewing conditions. In this study, a software module, based on mathematical transformations of the ciecam02 model, was designed and implemented. Unlike the previous software modules, which were allowing use of only a limited choice of common standardized icc display profiles, the developed module also allows the use of optimized profiles created by the user. This paper presents prediction of the appearance of test images with assigned different display profiles after changing illuminant. The two used optimized profiles, created by software characterization of specific lcd display, have a different display gamma value (1.8 and 2.2). It is observed that, after changing the initial cie d50 to a higher colour temperature illuminant (d65), the colours of images will be shifted to the blue hues, and, in the case of illuminant temperature less than d50 (a and f11), to yellow h...

2005

We developed the multiple primary color LCD's where the pixels were composed of red(R), green(G), blue(B), cyan(C), magenta(M) and yellow(Y) subpixels. The color gamut was extended 99% of NTSC standard, while the brightness was also increased by 15%, compared to the conventional RGB three primary color LCD's. To get a natural color image we designed the color coordinates and luminance levels of each six subpixles, and developed color algorithm to convert the RGB signal to RGBCMY signal.

Color Research & Application, 1995

To calibrate a CRT color monitor, several assumptions are often made about its performance, one of the most accepted being constant channel chromaticity. However, when the measurements are taken in a extendedjield of CRT screen, where it is ussumed that only one primary phosphor is excited, the relative spectral radiance of the other primary phosphors that are contained in that Jield also contributes, ifthe background luminance is not zero. This contribution is greater at low levels of RGB channel stimulaiion and would invalidate the results obtained with calibration methods based on the hypothesis ofconstancy Qf chromaticity coordinates ofRGB channels. We have studied this eflect on the calibration of the CRT color monitor and, as a result, we propose a calibration that takes this effect into account. To evaluate the accuracy of the method, we have calculated color diflerences between the chromaticity that we wanted to reproduce and the one displayed with the CIELUV color-dierence formula, and the color tolerances with the line element of MacAdam ellipses. 0 1995 John Wiley di Sons, Inc.

Journal of the Society for …, 2007

This study aims to develop an image-color-quality (ICQ) model for a 2-in. mobile transmissive liquid-crystal display (LCD). A hypothetical framework for ICQ judgment was made to visually assess ICQ based the cognitive processes of the human visual system (HVS), and then an illumination adaptive ICQ model applicable for various surround conditions was developed. The memory color reproduction ratio (MCRR) of a locally adapted region of interest in a complex image reproduced on a mobile display was first computed. The colorfulness index and luminance contrast for all of the pixels in the image were then calculated by a global adaptation process. Finally, an ICQ model including all of the three attributes was developed under dark conditions using an assessed set of psychophysical data. The model gave more accurate performance than the mean accuracy for all of the observers. It was also visually tested under three different outdoor conditions, including overcast, bright, and very bright conditions, and the illuminance level range was from 7000 to 35,000 to 70,000 lx. The effect of outdoor illumination could be quantified as an exponential decay function and the ICQ model could be extended to cover a wide variety of outdoor illuminations conditions.

Journal of the Society for Information Display, 2003

Two newly derived characterization models for a liquid-crystal (LC) display have been tested for five LC-based displays. Data measured from a series of test colors indicated that all LC-based displays showed similar characteristics, including an S-shaped tone curve and poor channel chromaticity constancy. Because they include a hyperbolic function in their definition, the models do not have analytical inverses, and so iterative mathematical techniques are applied. It was shown that a new characterization model based on a hyperbolic function fits the tone curve very accurately with only four coefficients per channel for any type of LCD. In addition, it was also shown that the first derivative of the function provides a means of accurate correction of the chromaticity variation.

Journal of Display Technology, 2010