Inverse display characterization: A two‐step parametric model for digital displays

Abstract— A simple additivity model is often used as a basic model for digital‐display characterization. However, such a simple model cannot satisfy the needs of demanding color‐management applications all the time. On the other hand, systematic sampling of the color space and 3‐D interpolation is an expensive method in terms of measurement and computation time when precision is needed. This paper presents an enhanced method to characterize the XYZ‐to‐RGB transform of a digital display. This parametric method exploits the independence between the luminance variation of the electro‐optic response and the colorimetric responses for certain display types. The model is generally applicable to digital displays, including 3‐DMD projectors, single DMDs, CRTs, LCDs, etc., if the independence condition is satisfied. While the problem to solve is a 3‐D‐to‐3‐D transformation (from XYZ to RGB), the proposed parametric model is the composition of a 2‐D transform followed by a 1‐D transform. The 2‐D transform manages the chromatic aspects and, in succession, the 1‐D transform manages the luminance variations. This parametric digital model is applicable in the field of color management, with the objective of characterizing digital displays and applying a reference look such as a film look.     

A geometrical approach for inverting display color‐characterization models

Abstract— Some display color‐characterization models are not easily inverted. This work proposes ways to build geometrical inverse models given any forward color‐characterization model. The main contribution is to propose and analyze several methods to optimize the 3‐D geometrical structure of an inverse color‐characterization model directly based on the forward model. Both the amount of data and their distribution in color space is especially focused on. Several optimization criteria, related either to an evaluation data set or to the geometrical structure itself, are considered. A practical case with several display devices, combining the different methods proposed in the article, are considered and analyzed.     

High‐end colorimetric display characterization using an adaptive training set

Abstract— A new, accurate, and technology‐independent display color‐characterization model is introduced. It is based on polyharmonic spline interpolation and on an optimized adaptive training data set. The establishment of this model is fully automatic and requires only a few minutes, making it efficient in a practical situation. The experimental results are very good for both the forward and inverse models. Typically, the proposed model yields an average model prediction error of about 1 ΔE^ab* unit or below for several displays. The maximum error is shown to be low as well.     

Color refinement using deep neural networks for enhancing color recognition in a projector‐camera system

In projector‐camera systems, object recognition is essential to enable users to interact with physical objects. Among several input features used by the object classifier, color information is widely used as it is easily obtainable. However, the color of an object seen by the camera changes due to the projected light from the projector, which degrades the recognition performance. To solve this problem, we propose a method to restore the original color of an object from the observed color through camera. The color refinement method has been developed based on the deep neural network. The inputs to the neural network are the color of the projector light as well as the observed color of the object in multiple color spaces, including RGB, HSV, HIS, and HSL. The neural network is trained in a supervised manner. Through a number of experiments, we show that our refinement method reduces the difference from the original color and improves the object recognition rate implemented with a number of classification methods.     

液晶显示器颜色特性化方法的对比研究

液晶显示器是目前最普遍的计算机显示设备之一。由于其颜色空间存在设备相关性,因此需要对液晶显示器进行特性化,即设备颜色空间映射为CIE标准色度空间。描述了液晶显示器的光电特性和颜色呈现机理;对目前已有的特性化方法进行分析;最后通过实验,比较了基于一维查找表的三种特性化方法的优劣。通过不同特性化方法颜色复现精度的对比,论证了黑底修正和最优化求解在液晶显示器特性化中的重要作用。     

How color break‐up occurs in the human‐visual system: The mechanism of the color break‐up phenomenon

Abstract— In the present set of experiments, we examined the mechanisms underlying color break‐up (CBU), a phenomenon observed when images produced with a color‐sequential projector are viewed. The perceived position of CBU was measured during fast eye movement, saccade with static and briefly flashed stimuli. Results showed that CBU did not simply correspond to the locus of the stimulus on the retina during saccades, because the width of the CBU perception was narrower than the distance of the eye movements. This effect was thought to be related to visual stability, which allows objects to be perceived as stationary even when the eyes move and the retinal image changes position. Visual stability is assumed to operate by compensating for the change in retinal image position using eye‐position signals; however, this compensation is imperfect during saccades. Thus, incomplete compensation results in a CBU perception that is of a narrower width than the amplitude of the saccade. In conclusion, CBU cannot be simulated with moving video cameras because it results largely from the mechanisms of visual perception. Large inter‐individual differences in perception of CBU were also found. This observation also supports the idea that CBU depends on the mechanism of perception.     

A carbon‐nanotube field‐emission display with simple electron‐beam trajectory control

Abstract— A unique gated cathode structure for a carbon‐nanotube‐based field‐emission display has been designed and built. This structure optimizes the electron‐beam profiles to assure a good color gamut and high anode efficiency without requiring specific focusing electrodes or structure. A computer simulation, written to analyze and improve the device design, shows good correlation with the experimental data and helps predict design margins. A full‐color frit‐sealed display built with this approach demonstrates an excellent color gamut of the phosphor, and the model predicts avenues for further color‐gamut improvements.     

Laser‐based multi‐user 3‐D display

Abstract— The development of a multi‐user stereoscopic display that does not require the use of special glasses (autostereoscopic), and that enables a large degree of freedom of viewer movement and requires only the minimum amount of information (a stereo pair) for the displays described. The optics comprise an RGB holographic laser projector that is controlled by the output of a multi‐target head‐position head tracker, an optical assembly that converts the projector output into steerable exit pupils, and a screen assembly comprising a single liquid‐crystal display (LCD) and image multiplexing screen. A stereo image pair is produced on the LCD by simultaneously displaying left and right images on alternate rows of pixels. Novel steering optics that replace the conventional backlight are used to direct viewing regions, referred to as exit pupils, to the appropriate viewers' eyes. The results obtained from the first version of the display, where the illumination source consists of several thousand white LEDs, are given and the current status of the latest prototype being constructed on the basis of these results is described. The work indicates that a laser‐based head‐tracking display can provide the basis for the next generation of 3‐D display.     

High‐accuracy system for spectral measurement of small‐area‐contrast and low‐light‐level display screens

Abstract— A double‐monochromator spectroradiometer with a photon‐counting detector will be described. The system captures spectroradiometric data with near‐perfect linearity over six decades of intensity and with wavelength uncertainties of under 0.05 nm. It enables accurate measurement of spectral radiance data and small‐area contrast with an uncertainty less than 0.002 in chromaticity (x,y) and 2% in luminance for a typical CRT spectrum.     

All‐additive ink‐jet‐printed display backplanes: Materials development and integration

Abstract— Methods used to deposit and integrate solution‐processed materials to fabricate TFT backplanes by ink‐jet printing are discussed. Thematerials studied allow the development of an all‐additive process in which materials are deposited only where their functionality is required. The metal layer and semiconductor are printed, and the solution‐processed dielectric is spin‐coated. Silver nanoparticles are used as gate and datametals, the semiconductor used is a polythiophene derivative (PQT‐12), and the gate dielectric is an epoxy‐based photopolymer. The maximum processing temperature used is 150°C, making the process compatible with flexible substrates. The I_ON/I_OFF ratio was found to be about 10⁵?10⁶, and TFT mobilities of 0.04 cm²/V‐sec were obtained. The influence of surface treatments on the size and shape of printed features is presented. It is shown that coffee‐stain effects can be controlled with ink formulation and that devices show the expected pixel response.     

MTF measurement method for medical displays by using a bar‐pattern image

Abstract— A modulation‐transfer‐function (MTF) measurement method that uses a bar‐pattern image for medical displays such as liquid‐crystal displays (LCDs) and cathode‐ray tubes (CRTs) has been investigated. A specific bar‐pattern image on the display was acquired with a high‐resolution single‐lens reflex‐type digital camera equipped with a close‐up lens. The MTF was calculated from the amplitudes of the fundamental‐frequency components, which were extracted from the profile data across the bar patterns by using Fourier analysis. Actual comparisons with the conventional line technique were performed for a medical CRT. The adequate accuracy and excellent reproducibility of the method were confirmed. Furthermore, unlike the line method, an advantageous feature which can use an input signal with sufficient amplitude was theoretically proved. Horizontal and vertical MTFs at the central position of the display area were measured up to the Nyquist frequency for several medical displays. From these measurements, this method has the capability to detect slight differences between the displays measured. This proposed method is useful in understanding and quantifying the medical display's performance due to excellent reproducibility and accuracy.     

Thermal transfer for flat‐panel‐display manufacturing

Abstract— Photolithography is currently the predominant patterning method in the flat‐panel‐display (FPD) industry. Thermal lithography is a novel approach offering superior process control, a completely dry process, and considerable cost savings. Thermal imaging is now the dominant imaging method in computer‐to‐plate applications in the printing industry, with over 6000 installations world‐wide. Two applications, in which this technology could be applied in the FPD industry, will be discussed in detail: color filters for liquid‐crystal displays (LCDs) and barrier ribs for LCDs and organic light‐emitting‐diode (OLED) displays.     

Ambient‐light‐adaptive image quality enhancement for full‐color e‐paper displays using a saturation‐based tone‐mapping method

Full‐color e‐paper displays that have a small color gamut encounter image tone distortions and contour artifacts in high‐saturation regions. To solve these issues, in this paper, we comprehensively measure the colorimetric responses of input image signals and demonstrate that the perceptual colorfulness in terms of chroma abnormally declines when the input saturation is beyond a certain value. Accordingly, saturation‐based tone‐mapping curves are developed to map the abnormal high saturation to the range that the display is able to normally render. By testing several test charts and natural images, the recoveries of the original image tones and the removals of the contour artifacts are experimentally verified. More important, by discussing how to conduct a database of tone‐mapping curves for different ambient lights and utilize the database for an unknown ambient light, the proposed method is proven to be completely ambient light adaptive.     

Masking model for accurate colorimetric characterization of LCD

Abstract— A color management system (CMS) such as ICC profile or sRGB space have been proposed for color transformation and reproduction of cross media. In such a CMS, accurate colorimetric characterization of a display device plays a critical role in achieving device‐independent color reproduction. In the case of a CRT, colorimetric characterization based on a GOG model is accurate enough for this purpose. However, there is no effective counterpart in liquid‐crystal displays (LCDs) since the characterization of an LCD has many difficulties, such as channel interaction and non‐constancy of channel chromaticity. In this paper, a new method of display characterization is proposed which is applicable to the assessment of color reproduction of LCDs. The proposed method characterizes an electro‐optical transfer function considering both channel interaction and non‐constancy of channel chromaticity. Experimental results show that the proposed method is very effective in the colorimetry of LCDs.     

A field‐sequential‐color display with a local‐primary‐desaturation backlight scheme

Abstract— Field‐sequential‐color technology eliminates the need for color filters in liquid‐crystal displays (LCDs) and results in significant power savings and higher resolution. But the LCD suffers from color breakup, which degrades image quality and limits practical applications. By controlling the backlight temporally and spatially, a so‐called local‐primary‐desaturation (LPD) backlight scheme was developed and implemented in a 180‐Hz optically compensated bend (OCB) mode LCD equipped with a backlight consisting of a matrix of light‐emitting diodes (LEDs). It restores image quality by suppressing color breakup and saves power because it has no color filter and uses local dimming. A perceptual experiment was implemented for verification, and the results showed that a field‐sequential‐color display with a local‐primary‐desaturation backlight reduced the color breakup from very annoying to not annoying and even invisible.     

基于人工神经网络的CCD数码相机颜色特征化

阐述了基于BP神经网络的数码相机特征化方法。采用不同的神经网络结构,建立了数码相机记录的RGB信息和原影像C IEXYZ色度信息之间的非线性对应关系。对NIKON D200数码相机进行了研究,通过实验得到了合理的神经网络结构为3—10—10—3。测试不同的训练样本和测试样本,达到的C IELAB平均色差和最大色差分别为1.9~2.2和6.7~7.4个色差单位。讨论了实验设备的重复性,同时,分析了样本数量对实验结果的影响。实验结果表明:对数码相机的特征化,可采用BP神经网络技术实现较高的精度。     

Color‐conversion method for a multi‐primary display to reduce power consumption and conversion time

Abstract— A color‐conversion method for a light‐emitting multi‐primary‐color display is proposed. While amulti‐primary‐color display uses four or more primary colors to reproduce a wide color gamut, multiple sets of primary‐color signals are needed to reproduce one color. Therefore, linear programming, which results in low power consumption, was adopted to uniquely determine the set of primary‐color signals. Although a highly accurate color conversion was achieved by using linear programming with low power consumption, it requires a very long time to convert colors of high‐resolution images. Therefore, by categorizing the color conversion of linear programming as a classification problem, colors are converted by using the decision‐tree method, which is a classification method. As a result, color conversion with high accuracy, low power consumption, and short conversion time was achieved.     

Conjugate‐optical retroreflector display system: Optical principles and perceptual issues

Abstract— Conjugate‐optical retroreflector (COR) display systems have the potential for providing inexpensive high‐resolution imagery in a head‐mounted display (HMD) configuration. There are several perceptual issues, however, that need to be addressed before a COR display system can be used effectively. One issue is the choice of projected‐image location relative to the retroreflective screen, which is determined by the convergence angle between the binocular channels of the COR display. Another issue involves visual half‐occlusions, which can occur when a portion of a stereoscopic image is visible to only one eye, as may occur in any HMD. If half occlusions are simulated in a COR display in a way that is inconsistent with natural viewing, undesirable perceptual effects may result. In the present paper, we first describe, the optical principles that underlie the COR display system. We then discuss the importance of binocular convergence and describe a COR display configuration that eliminates inconsistencies in the depth cues provided by displayed surface properties and halfocclusions.     

Efficient and compact green laser for micro‐projector applications

Abstract— Efficient and compact green lasers are keystone components for micro‐projector applications in mobile devices. An architecture that consists of an infrared‐producing DBR (distributed Bragg reflector) laser with a frequency‐doubling crystal is used to synthesize a green laser that has high electrical‐to‐optical conversion efficiency and can be modulated at speeds required for scanner‐based projectors. The design and performance of a green‐laser package that uses adaptive optics to overcome the challenge of maintaining alignment between the waveguides of the DBR laser and the frequency‐doubling crystal over temperature and lifetime is described. The adaptive optics technology that is employed uses the piezo‐based smooth impact drive mechanism (SIDM) actuators that offer a very small step size and a range of travel adequate for the alignment operation. The laser is shown to be compact (0.7 cm³ in volume) and capable of a wall‐plug efficiency approaching 10% (at 100‐mW green power). It was demonstrated that the adaptive optics enables operation over a wide temperature range (10–60°C) and provides the capability for low‐cost assembly of the device.