Starting from our previously proposed line element and considering more “surface color” datasets, we derive a simplified version which matches experimental datasets equally well and resulted into a conformally-Euclidean line element, which is conceptually much simpler than any existing color difference metrics. The color difference is written as an Euclidean difference multiplied with a simple factor which depends on the luminance only. In a subspace with constant luminance, as considered by MacAdam, this factor becomes constant and the subspace is flat. The same holds for sufficiently large luminances. Based on this LE we derive perceptual coordinates (A,l_c,s_c) very similar to the CIELab (L^*,a^*,b^*).

We made a detailed review of the difference measures which have been used to judge the differences between experimentally determined color differences and theoretically defined ones, so-called line elements, for the human visual system. To eliminate the statistical errors due to variable and usually arbitrary sampling of the directions in a color point, we integrate the measures over a complete ellipsoid/ellipse. It turns out that in the limit for small deviations from circularity all proposed measures (V_AB, γ-1, CV and STRESS) are equivalent. For greater deviations the measures become distinct with γ-1 the most sensitive and STRESS the least. Ideally a difference measure should be coordinate independent and then it is advantageous to apply an affine transformation to both sets, e.g. turning the theoretical one into the unit ball. Although MacAdam already used this method but sampled the transformed ellipse, we integrate over the ellipsoid/ellipse. Comparing the results with the base measures we show that only STRESS is coordinate independent. Judging whether a single ellipsoid/ellipse resembles a unit ball can easily be done by comparing the eigenvalues with one and we show that our previously proposed error measure d_ev (Candry e.a. Optics Express, 30, 36307, 2022) is the eigenvalue version of γ-1. We show why the short lived correlation coefficient r was justly abandoned, being very coordinate dependent, but that Pant's recent geometric measure 1-R on the other hand is coordinate independent. All measures are routinely made scale invariant by the introduction of a scaling parameter, to be optimized. Lastly we show that from all measures the γ-1 ones are the only ones permitting the simple derivation of the globally optimized difference measure from the locally defined ones.

Several studies report on the sensitivity of human vision to static spatial sinusoidal achromatic and chromatic contrast variations. However, a Riemannian color difference metric, which includes the spatial and colorimetric properties of sinusoidal gratings, is lacking. Such a metric is important for various applications. Here we report on the development of a new Riemannian metric, for the prediction of detection ellipsoids in color space, for spatial sinusoidal gratings as a function of the grating’s size, spatial frequency, luminance and chromaticity. The metric is based on measurements and models of achromatic and isoluminous chromatic contrast sensitivity functions available in literature, and the Riemannian metric for split fields which we reported earlier. We find adequate agreement with various data sets of experimental achromatic and isoluminous chromatic contrast sensitivity functions and with experimentally determined threshold ellipses of isoluminous chromatic Gabor gratings.

We developed a new Riemannian color difference metric based on Friele's line element and the results of psychophysical color discrimination experiments. Visual adaptation effects are incorporated into the model. This new color difference metric was validated against various data sets available in the literature. We found adequate agreement with experimentally determined threshold ellipsoids/ellipses and a better threshold predictability compared with other color difference metrics. The new Riemannian color difference metric was applied for the calculation of the color gamut volume and the maximum number of mutually discernible colors.

For the calculation of the color gamut volume and the maximum number of mutually discernible colors, an algorithm based on a Riemannian metric and the densest packing of spheres is proposed. With this algorithm, the color gamut volume was calculated for the conditions of experiments reported in literature. Good agreement was found with the experimental findings of the color gamut volume as a function of the peak luminance. Using the new algorithm, the color gamut volume and the maximum number of mutually discernible colors was calculated for various sets of primary colors corresponding to display standards and various dynamic ranges. Comparisons were made with state-of-the-art methods which are based on the Euclidean metric in approximately uniform color spaces and a simple cubic lattice. It was found that the state-of-the-art methods underestimate the maximum number of mutually discernible colors. However, the relative differences decrease as the primary colors are more saturated. Based on the new algorithm the maximum number of mutually discernible colors was calculated for a range of peak retinal illuminance levels and various sets of primary colors. We found that, for a given set of primary colors, the maximum number of mutually discernible colors is proportional to the logarithm of the ratio of the peak retinal illuminance level and a fitting parameter.

It is generally accepted that the perceptual color space is not Euclidean. A new line element for a 3-dimensional Riemannian color space was developed. This line element is based on the Friele line elements and psychophysical color discrimination models, and comprises both the first and second stage of color vision. The line element is expressed in a contrast space based on the MacLeod-Boynton chromaticities. New equations for the contrast thresholds along the cardinal axes and new metric tensor elements were determined. Visual adaptation effects were incorporated into the model. Color discrimination threshold ellipsoids were calculated with the new line element. Adequate agreement with experimental threshold ellipsoids reported in literature was demonstrated. From a comparison with other color difference metrics a better overall predictability of threshold ellipsoids was found with the new line element.

SID Symposium Digest of Technical PapersVolume 52, Issue S1 p. 268-268 Technical Sessions: Session 38: OLED Device (OLEDs)Free to Read 38.2: Temperature Dependency and Aging of OLED Displays Frédérique Chesterman, Frédérique Chesterman ELIS Department, Ghent University, Ghent, Belgium Barco, Kortrijk, BelgiumSearch for more papers by this authorTom Kimpe, Tom Kimpe Barco, Kortrijk, BelgiumSearch for more papers by this authorPatrick De Visschere, Patrick De Visschere ELIS Department, Ghent University, Ghent, BelgiumSearch for more papers by this authorKristiaan Neyts, Kristiaan Neyts ELIS Department, Ghent University, Ghent, BelgiumSearch for more papers by this author Frédérique Chesterman, Frédérique Chesterman ELIS Department, Ghent University, Ghent, Belgium Barco, Kortrijk, BelgiumSearch for more papers by this authorTom Kimpe, Tom Kimpe Barco, Kortrijk, BelgiumSearch for more papers by this authorPatrick De Visschere, Patrick De Visschere ELIS Department, Ghent University, Ghent, BelgiumSearch for more papers by this authorKristiaan Neyts, Kristiaan Neyts ELIS Department, Ghent University, Ghent, BelgiumSearch for more papers by this author First published: 24 February 2021 https://doi.org/10.1002/sdtp.14453AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume52, IssueS1International Conference on Display Technology (ICDT 2020)February 2021Pages 268-268 RelatedInformation

In this paper, the influence of temperature on the luminance of an organic light-emitting device (OLED) display is investigated. Luminance, temperature, and power measurements are executed on a 55-in white-red-green-blue active-matrix-OLED display with a resolution of 1920 x 1080 and an oxide-thin-film-transistor (TFT) backplane, under a controlled, static temperature environment. The measurements indicate a strong influence of temperature on the luminance of the display, resulting from the temperature dependence of both the TFT and the OLED. The influence of temperature on the luminance of an OLED display is also investigated in a dynamic context. Measurements show that temperature changes resulting from losses in the display have an important influence on the luminance stability of the display. The measurements linking luminance and temperature in a static temperature environment allow estimating the change in luminance in a dynamic context. Finally, this paper presents the results of a number of experiments that were set up to show scenarios in which the temperature dependence of the display's luminance has a direct negative impact on the picture quality of the display. The results of this work show that the thermal behavior of an OLED display must be taken into account when working towards a high-performing OLED display.

The space-charge-limited current in a zero thickness planar thin film depends on the geometry of the electrodes. We present a theory which is to a large extent analytical and applicable to many different lay-outs. We show that a space-charge-limited current can only be sustained if the emitting electrode induces a singularity in the field and if the singularity induced by the collecting electrode is not too strong. For those lay-outs where no space-charge-limited current can be sustained for a zero thickness film, the real thickness of the film must be taken into account using a numerical model.

This paper describes how long-term use impacts the light output of a commercial 55” WRGB AMOLED display with InGaZnO TFT backplane. This covers effects which are known by the terms “aging”, “image-sticking,” and “burn-in.” The focus is on three different observations: permanent change in light output as a function of time, permanent screen burn-in, and permanent shift in color point. From this work it can be concluded that state-of-the-art OLED displays still suffer from light output instability under prolonged stress. The results suggest that the permanent change in light output can be explained by the combination of three different phenomena: a decrease in efficiency of the OLEDs as a function of time for active subpixels, a positive threshold voltage shift of the driving transistor for active subpixels, and a negative threshold voltage shift of the driving transistor for inactive subpixels, if they are illuminated and/or kept at high temperature. To our knowledge, this is the first work that describes and quantifies the permanent change in light output of a commercial WRGB OLED panel with InGaZnO TFT backplane. It sheds light on which effects occur and can be a valuable tool, both in the design and optimization of OLED panels and in the determining the circumstances under which this technology may be applicable.

This paper explains how a non-uniform temperature distribution arises across an OLED display and how it is influenced by the image content. IR camera measurements on a sample 55” WRGB OLED display and a thermal model that allows simulating the temperature distribution across an OLED display are presented. It has been shown before that temperature has a direct impact on the picture quality of an OLED display. Therefore, a good understanding of the thermal behavior of an OLED display is important. The presented thermal model can be a useful tool in the design phase of an OLED display.

The tendency of the display market is towards displays with higher resolutions. Therefore, patterned retarder-based stereoscopic displays require smaller front glass thickness to maintain good vertical viewing angle and limited crosstalk. To properly design these stereoscopic displays and quantify these requirements, we developed a simulation platform to predict radiance, polarization profile, and crosstalk over viewing angles and over wavelengths. Tunable parameters such as the distance between the pixels and the patterned retarder, and the optical properties of the patterned retarder are included. The simulation platform has been validated by comparing outcomes of simulations with measurements. We predict crosstalk accounting for both the human eye field of view and the diameter of the pupil. We found that to obtain a vertical viewing angle of at least +/- 30 degrees and crosstalk of at most 0.11 for a display with a pixel pitch beyond 0.27mm, the display should include black absorbers, and the thickness of the front glass should be at most 0.5mm. For higher resolution displays (pixel pitch no more than 0.21mm), a front glass thickness at most 0.15mm is required to produce a vertical viewing angle beyond +/- 14 degrees and a minimum viewing distance of 0.3m.

In this paper, the power consumption of a white-red-green-blue (WRGB) active-matrix organic light-emitting device (OLED) display and the resulting temperature distribution across the display are analyzed as a function of the applied image and the luminance of the emitted light. It has been shown previously that temperature directly impacts the picture quality of an OLED display. Luminance, spectral radiance, power and temperature measurements are performed on a 55-in WRGB OLED display with a resolution of 1920 1080. A power model is presented that allows calculating the display's power consumption for a given applied image. This involves the dependency of the efficiency of the white OLED on the current density, the wavelength dependent transmission of the color filters and the contribution of each of the subpixels in producing the display's nominal white. The output of the power model is used as input for a basic thermal model that simulates the temperature distribution across the display. The thermal model is based on 3D computational fluid dynamics analysis framework (FloEFD). A good agreement between the simulations and measurements on the sample WRGB OLED display is obtained.

Organic Light Emitting Diodes consist of a stack of thin layers that have a high refractive index and may have anisotropic optical properties. The emission from such a planar structure depends on the layering of the OLED, the anisotropy of the different materials and the orientation of the dipole emitters in the organic layer. OLEDs are used in lighting and display devices and the requirements for both applications are very different.

Anisotropy in a material can have an important influence on the light emission properties. The main effect is that the atoms, molecules or nanoparticles that emit light may have a preferential orientation. When the light emission is due to an electrical dipole transition along a certain axis, most light will be emitted in the plane perpendicular to that axis. The optical anisotropy of the material further determines how the refractive index of the light depends on the polarization and propagation direction of the light. The emission from oriented emitters in structures consisting of anisotropic layers can be determined with a simulation tool [1]. This tool has been used to predict the emission pattern for OLEDs with oriented dipole emitters and for CLCs with fluorescent dyes.

In this paper we investigate the performance of a transparent photoconductive sensor based on a double layer of organic materials (m-MTDAB / PTCBI) which are deposited on two interdigitated transparent ITO electrodes. The performance of the sensor is demonstrated with electro-optical measurements: the I(V) curves consist of two linear sections meeting at a knee voltage V-t. Linear regression performed on the I(V) curves below V-t show that the conductance is a power law of the luminance incident on the device. We present a model to describe the behaviour of the sensor below V-t.We present measurements of I(t) for a transient illumination of the sensor. Plotting the inverse of the current as a function of time we find that the transient is consistent with the model for voltages below V-t. For voltages above V-t we find that the sensor behaves like a resistor in series with a space charge (SC) region. We present a local illumination experiment that confirms the existence of a SC region between the electrodes of the photoconductive sensor for V>V-t. The space charge region is located near the cathode of the sensor.