Luminance Range Research Articles

Fine-grained detection of inverse tone mapping in HDR images

Abstract High dynamic range (HDR) imaging enables to capture the full range of physical luminance of a real-world scene, and is expected to progressively replace traditional low dynamic range (LDR) pictures and videos. Despite the increasing HDR popularity, very little attention has been devoted to new forensic problems that are characteristic to this content. In this paper, we address for the first time such kind of problem, by identifying the source of an HDR picture. Specifically, we consider the two currently most common techniques to generate an HDR image: by fusing multiple LDR images with different exposure time, or by inverse tone mapping an LDR picture. We show that, in order to apply conventional forensic tools to HDR images, they need to be properly preprocessed, and we propose and evaluate a few simple HDR forensic preprocessing strategies for this purpose. In addition, we propose a new forensic feature based on Fisher scores, calculated under Gaussian mixture models. We show that the proposed feature outperforms the popular SPAM features in classifying the HDR image source on image blocks as small as 3 × 3, which makes our method suitable to detect composite forgeries combining HDR patches originating from different acquisition processes.

Global Localization Using Low-frequency Image-based Descriptor and Range Data-based Validation

In image-based global localization, a robot pose is estimated through image association when the robot revisits a previously visited location on a map. Image association is typically performed using high-level local features such as scale invariant feature transform (SIFT) and speeded up robust feature (SURF). However, these methods suffer from false-positive association and high computational load to reject outliers. In this study, we introduce a novel global localization method based on the proposed low-frequency image-based descriptor (LFID) and laser range data. The image is first processed by reducing the range of luminance in the frequency domain. Visual features are then extracted from the processed image through a kernel window. These visual features are described as binary representation for fast association. Because this binary representation includes a spatial distribution of features, it can minimize false-positive association. Nevertheless, false-positive association could occur when scenes appear to be similar from different viewpoints. To address this problem, this study adopts a laser rangefinder to validate the similarity of the place and reject false-positives from the scene recognition. Experimental results confirm the effectiveness of the proposed scheme in actual indoor environments.

78‐3: 2D Representation of Display Color Gamut

Display gamuts usually render complex shapes in a uniform color space, requiring observers to change views to comprehend a 3D plot. We propose a 2D representation of a display color gamut, named “gamut rings,” where the area within an arbitrary luminance and hue angle range corresponds to gamut volume.

Characterization of electronic displays using CMOS single‐photon avalanche diode image sensors

AbstractAdvanced complementary metal‐oxide semiconductor‐compatible single‐photon avalanche diode array technology is progressing rapidly and is being deployed in a wide range of applications. We report for the first time the use of a complementary metal‐oxide semiconductor‐compatible single‐photon avalanche diode array to perform detailed optical measurements on pixels of an organic light‐emitting diode microdisplay at very high sampling rate, very low light level, and over a very wide dynamic range of luminance. This offers a clear demonstration of the huge potential of this single‐photon avalanche diode technology to reveal hitherto obscure details of the optical characteristics of individual and groups of organic light‐emitting diode pixels.

High dynamic range ultrasound imaging.

High dynamic range (HDR) imaging is a popular computational photography technique that has found its way into every modern smartphone and camera. In HDR imaging, images acquired at different exposures are combined to increase the luminance range of the final image, thereby extending the limited dynamic range of the camera. Ultrasound imaging suffers from limited dynamic range as well; at higher power levels, the hyperechogenic tissue is overexposed, whereas at lower power levels, hypoechogenic tissue details are not visible. In this work, we apply HDR techniques to ultrasound imaging, where we combine ultrasound images acquired at different power levels to improve the level of detail visible in the final image. Ultrasound images of ex vivo and in vivo tissue are acquired at different acoustic power levels and then combined to generate HDR ultrasound (HDR-US) images. The performance of five tone mapping operators is quantitatively evaluated using a similarity metric to determine the most suitable mapping for HDR-US imaging. The ex vivo and in vivo results demonstrated that HDR-US imaging enables visualizing both hyper- and hypoechogenic tissue at once in a single image. The Durand tone mapping operator preserved the most amount of detail across the dynamic range. Our results strongly suggest that HDR-US imaging can improve the utility of ultrasound in image-based diagnosis and procedure guidance.

Compression Efficiency of High Dynamic Range and Wide Color Gamut Pixel’s Representation

Ultra-high definition (UHD) is currently being deployed in video distribution pipelines for improved quality of experience. This new recommendation not only improves spatial and temporal resolution, but also the quality and accuracy of pixels using wide color gamut (WCG) and high dynamic range (HDR) technologies. Indeed, HDR video technology aims at conveying the full range of perceptible shadow and highlight details with enough different tonal levels to prevent loss of visual information, while WCG increases the amount of visible color that can be represented. However, these technologies require different standard digital pixel representations than the ones currently employed in high definition (HD) television. While the impact of increasing spatial and temporal resolution (i.e., increase of resolution and frame rate) on compression efficiency has already been assessed, it is not clear how new pixel representations would affect the compression performance. In this paper, we discuss the differences between HD color pixel representation and the newly standardized representations developed to meet the requirements introduced by WCG and HDR. Moreover we explain why existing HD pixel representations are sub-efficient for encoding HDR and WCG pixels. We also perform a statistical analysis of pixel distribution in real images to explain how pixel’s representation influences compression efficiency. Results show that by tailoring a pixel representation upon the range of luminance and color values accessible in content and displays, bandwidth savings can be achieved while increasing the quality of delivered content. We conclude this paper by discussing the shortcomings of the color pixel representation recommended for the UHD television standards and provide guidelines to create a more efficient one.

Solution-Processed Warm White Organic Light-Emitting Diodes Based on a Blue Thermally Activated Delayed Fluorescence Dendrimer.

Thermally activated delayed fluorescence (TADF) emitters have received much attention for the fabrication of white organic light-emitting diodes (WOLEDs); however, challenges remain owing to severe efficiency roll-off, poor color stability, and high cost. In this contribution, solution-processed hybrid WOLEDs were obtained by employing a blue TADF dendrimer, bis{4-[3,6-bis(3,6-di-tert-butylcarbazol-N-yl)carbazol-N-yl]phenyl}sulfone (BPS), combined with an orange iridium complex, bis(2-phenylbenzothiazolato)(acetylacetonate)iridium(III), Ir(bt)2 (acac), as a co-dopant. The devices achieved a maximum external quantum efficiency of 6.59 % and a maximum current efficiency of 17.34 cd A-1 . The results suggest that the TADF dendrimer serving as an assistant dopant were helpful in reducing the triplet populations by up-converting the triplet excitons to the singlet state and immediately transferring the singlet excitons to Ir(bt)2 (acac) (bt=2-phenylbenzothiazolato, acac=acetylacetonato) by virtue of the long-range Förster resonance energy transfer, thus significantly decreasing the triplet-triplet annihilation (TTA). Moreover, the emitters can act as shallow trapping centers to decrease charge and exciton aggregation. The resulting OLEDs exhibit stable electroluminescent spectra and low efficiency roll-off at relatively high current density. The CIE coordinates Δ(x, y) vary only (0.02, 0.02) in the luminance range of 100 to 10 000 cd m-2 .

Parameters of motion vision in low light in the hawkmoth Manduca sexta.

The hawkmoth Manduca sexta is nocturnally active, beginning its flight activity at sunset, and executing rapid controlled maneuvers to search for food and mates in dim light conditions. The visual system of this moth has been shown to trade off spatial and temporal resolution for increased sensitivity in these conditions. The study presented here uses tethered flying moths to characterize the flight performance envelope of the wide-field-motion-triggered steering response of M. sexta in low light conditions by measuring attempted turning in response to wide-field visual motion. Moths were challenged with a horizontally oscillating sinusoidal grating at a range of luminance, from daylight to starlight conditions. The impact of luminance on response to a range of temporal frequencies and spatial wavelengths was assessed across a range of pattern contrasts. The optomotor response decreased as a function of decreasing luminance, and the lower limit of the moth's contrast sensitivity was found to be between 1 and 5%. The preferred spatial frequency for M. sexta increased from 0.06 to 0.3cyclesdeg-1 as the luminance decreased, but the preferred temporal frequency remained stable at 4.5 Hz across all conditions. The relationship between the optomotor response time to the temporal frequency of the pattern movement did not vary significantly with luminance levels. Taken together, these results suggest that the behavioral response to wide-field visual input in M. sexta is adapted to operate during crepuscular to nocturnal luminance levels, and the decreasing light levels experienced during that period changes visual acuity and does not affect their response time significantly.

Combining emissions of hole- and electron-transporting layers simultaneously for simple blue and white organic light-emitting diodes with superior device performance

Combining emissions of hole- and electron-transporting layers simultaneously, a simple four-color hybrid white OLED realizes good white emission with a maximum CRI of 93–94 over a wide luminance range of 83.68–17 050 cd m−2, and also achieves a high EQE of 18.44%.

Efficient Red/Green/Blue Tandem Quantum-Dot Light-Emitting Diodes with External Quantum Efficiency Exceeding 21.

Highly efficient tandem quantum-dot light-emitting diodes (QLEDs) are developed by using an interconnecting layer (ICL) with the structure of ZnMgO/Al/HATCN/MoO3. The developed ICL exhibits high transparency, efficient charge generation/injection capability, and high robustness to resist solvent damage during deposition of the upper functional layers. With the proposed ICL, full color (red/green/blue, R/G/B) tandem QLEDs are demonstrated with extremely high current efficiency and external quantum efficiency (EQE): 17.9 cd/A and 21.4% for B-QLEDs, 121.5 cd/A and 27.6% for G-QLEDs, 41.5 cd/A and 23.1% for R-QLEDs. To the best of our knowledge, these are the highest values ever reported. In addition, the EQEs of R-, G-, and B-QLEDs all exceed 21%. The high efficiency can be well maintained over a wide range of luminance from 102 to 104 cd/m2. For example, even at a high brightness of 20 000 cd/m2, the EQE of R-, G-, and B-QLEDs can still sustain its 96%, 99%, and 78% maximum value, respectively. The demonstrated full-color tandem QLEDs, with extremely high efficiency, long operational lifetime, low roll-off efficiency, and high color purity, would be ideal candidates to bring QLEDs into the next generation of full-color displays and the solid-state lighting market.

Generative adversarial dehaze mapping nets

Single image haze removal is a challenging task with few effective constraints, which seriously affect performance of machine learning algorithms. In this paper, we propose a Generative Adversarial Dehaze Mapping Nets (GADMN) to estimate a medium transmission for an input hazy image. GADMN adopts Generative Adversarial Nets (GAN) based deep architecture, which maps haze-relevant features to medium transmission and uses the network to carry on the feedback restrain. We also propose a multiple-light scattering model, which adds artificial light source and diffuses reflection light emerged from reflected light in the mist. Since the interference light is estimated in this model, we name it Local Multi-scale Hierarchical Prediction Method (LMHPM), which is beneficial to recover the large luminance range image. Experimental result demonstrates that the proposed algorithm outperforms state-of-the-art methods, and exhibits better robustness and adaptability.

Highly-efficient tandem organic light-emitting device employing bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimi-dine doped with cesium azide in charge generation unit

Abstract In this research, we have investigated the charge generation and electron injection processes in charge generation unit (CGU) consisting of CsN3-doped Bis-4, 6-(3, 5-di-3-pyridylphenyl)-2-methylpyrimi-dine (CsN3:B3PYMPM)/Al/1, 4, 5, 8, 9, 11-Hexaazatriphenylene-hexacarbonitrile (HAT-CN). By employing this CGU, a high-efficiency phosphorescent tandem device achieving best efficiencies of 164.3 cd/A, 46.51% and 109.8 lm/W has been realized. Particularly, in addition to the improvement in current efficiency by more than two times, the tandem device has better power efficiency compared to the corresponding single-unit device at the same current density. Simultaneously, an efficient tandem white OLED showing high color stability and warm white emission over a wide range of luminance has been also fabricated.

HDR image reconstruction from a single exposure using deep CNNs

Camera sensors can only capture a limited range of luminance simultaneously, and in order to create high dynamic range (HDR) images a set of different exposures are typically combined. In this paper we address the problem of predicting information that have been lost in saturated image areas, in order to enable HDR reconstruction from a single exposure. We show that this problem is well-suited for deep learning algorithms, and propose a deep convolutional neural network (CNN) that is specifically designed taking into account the challenges in predicting HDR values. To train the CNN we gather a large dataset of HDR images, which we augment by simulating sensor saturation for a range of cameras. To further boost robustness, we pre-train the CNN on a simulated HDR dataset created from a subset of the MIT Places database. We demonstrate that our approach can reconstruct high-resolution visually convincing HDR results in a wide range of situations, and that it generalizes well to reconstruction of images captured with arbitrary and low-end cameras that use unknown camera response functions and post-processing. Furthermore, we compare to existing methods for HDR expansion, and show high quality results also for image based lighting. Finally, we evaluate the results in a subjective experiment performed on an HDR display. This shows that the reconstructed HDR images are visually convincing, with large improvements as compared to existing methods.

Binocular combination of luminance profiles.

We develop and test a new two-dimensional model for binocular combination of the two eyes' luminance profiles. For first-order stimuli, the model assumes that one eye's luminance profile first goes through a luminance compressor, receives gain-control and gain-enhancement from the other eye, and then linearly combines the other eye's output profile. For second-order stimuli, rectification is added in the signal path of the model before the binocular combination site. Both the total contrast and luminance energies, weighted sums over both the space and spatial-frequency domains, were used in the interocular gain-control, while only the total contrast energy was used in the interocular gain-enhancement. To challenge the model, we performed a binocular brightness matching experiment over a large range of background and target luminances. The target stimulus was a dichoptic disc with a sharp edge that has an increment or decrement luminance from its background. The disk's interocular luminance ratio varied from trial to trial. To refine the model we tested three luminance compressors, five nested binocular combination models (including the Ding–Sperling and the DSKL models), and examined the presence or absence of total luminance energy in the model. We found that (1) installing a luminance compressor, either a logarithmic luminance function or luminance gain-control, (2) including both contrast and luminance energies, and (3) adding interocular gain-enhancement (the DSKL model) to a combined model significantly improved its performance. The combined model provides a systematic account of binocular luminance summation over a large range of luminance input levels. It gives a unified explanation of Fechner's paradox observed on a dark background, and a winner-take-all phenomenon observed on a light background. To further test the model, we conducted two additional experiments: luminance summation of discs with asymmetric contour information (Experiment 2), similar to Levelt (1965) and binocular combination of second-order contrast-modulated gratings (Experiment 3). We used the model obtained in Experiment 1 to predict the results of Experiments 2 and 3 and the results of our previous studies. Model simulations further refined the contrast space weight and contrast sensitivity functions that are installed in the model, and provide a reasonable account for rebalancing of imbalanced binocular vision by reducing the mean luminance in the dominant eye.

High Dynamic Range Imaging Technology [Lecture Notes

In this lecture note, we describe high dynamic range (HDR) imaging systems; such systems are able to represent luminances of much larger brightness and, typically, also a larger range of colors than conventional standard dynamic range (SDR) imaging systems. The larger luminance range greatly improve the overall quality of visual content, making it appears much more realistic and appealing to observers. HDR is one of the key technologies of the future imaging pipeline, which will change the way the digital visual content is represented and manipulated today.

Efficient, color-stable and high color-rendering-index white organic light-emitting diodes employing full thermally activated delayed fluorescence system

Abstract High efficiency, high color rendering index (CRI) and excellent color-stability are important requirements for high-performance white organic light emitting diodes (WOLEDs). To realize these issues for the WOLEDs based on the full thermally activated delayed fluorescence (TADF) system, we constructed WOLED devices by employing CDBP:PO-T2T exciplex as the host, while 2CzPN and AnbTPA as blue and red dopants, respectively. We carefully optimize the device to realize balanced carrier transporting property of each emitting layer and good exciton confinement in the device. As a result, the WOLED achieves stable white emission with a high CRI of 82, a CIE coordinate of (0.33, 0.38) at a luminance of 1000 cd m −2 , and a small CIE variation value of (0.00, 0.02) in the luminance range of 100–3000 cd m −2 . It also demonstrates high maximum forward-viewing external quantum efficiency of 19.2%, current efficiency of 36.7 cd A −1 and power efficiency of 46.2 lm W −1 . Our work presents a novel and useful approach to develop highly efficient, color-stable and high-CRI WOLEDs through the full TADF mechanism.

Perceptual Lightness Modeling for High-Dynamic-Range Imaging

The human visual system (HVS) non-linearly processes light from the real world, allowing us to perceive detail over a wide range of illumination. Although models that describe this non-linearity are constructed based on psycho-visual experiments, they generally apply to a limited range of illumination and therefore may not fully explain the behavior of the HVS under more extreme illumination conditions. We propose a modified experimental protocol for measuring visual responses to emissive stimuli that do not require participant training, nor requiring the exclusion of non-expert participants. Furthermore, the protocol can be applied to stimuli covering an extended luminance range. Based on the outcome of our experiment, we propose a new model describing lightness response over an extended luminance range. The model can be integrated with existing color appearance models or perceptual color spaces. To demonstrate the effectiveness of our model in high dynamic range applications, we evaluate its suitability for dynamic range expansion relative to existing solutions.

Employment of gold-coated silver nanowires as transparent conductive electrode for organic light emitting diodes

This study proposes a simple method of Au coating on silver nanowires (Ag NWs) transparent conductive films as the anode of organic light emitting diodes (OLED) to increase the work function of the film and thus enhance hole transport. We carefully engineer the process conditions (pretreatment, solution concentrations, and coating number) of the coating using a diluted HAuCl4 solution on the Ag NWs film to minimize etching damage on Ag NWs accompanying the galvanic replacement reaction. Ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy show work function increase of Ag NWs upon Au coating. OLED devices based on Au-coated Ag NWs show a lower turn-on voltage and higher luminance, compared with pristine Ag NWs device. Although the Ag NWs device displays poor efficiencies in the low luminance range due to a high leakage, some of the Au-coated Ag NWs devices showed efficiencies higher than those of the ITO device in a high luminance.

Pure white organic light-emitting devices with excellent color stability using a non-doped 4-aryloxy-1,8-naphthalimide derivative

Pure white organic light emitting devices (OLEDs) with high color stability have been fabricated, using a 4-aryloxy-1,8-naphthalimide derivative FluONI as a non-doped blue emitting layer (EML) combined with orange emitting exciplex at the interface of electron donor/FluONI. Three kinds of hole transport materials consisting of amino groups with stepped highest occupied molecular orbital (HOMO) levels are introduced as electron donors for the modulations of exciplex emission band and hole injection barrier. As a result, pure white emission with a standard Commission Internationale de 1'Eclairage (CIE) coordinate of (0.33, 0.33) is achieved by adopting N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine as an electron donor with a relatively deep HOMO level and a 30nm-thick EML. Meanwhile, excellent color stability is also observed with a slight CIE coordinates shift of (0.01, 0.01) at a luminance range from 100 to 4000cd/m2. According to the systematic analyses on electroluminescence spectra, the pure white emission benefits from the broad emission bands of both FluONI and exciplex. The pure white emission with high color stability at different drive voltages are attributed to the sustainable equilibrium between FluONI intrinsic and exciplex emission. Our devices based on a single non-doped EML provide a simple way to realize color pure and stable white OLEDs.

Efficacy and safety of voretigene neparvovec (AAV2-hRPE65v2) in patients with RPE65-mediated inherited retinal dystrophy: a randomised, controlled, open-label, phase 3 trial

Phase 1 studies have shown potential benefit of gene replacement in RPE65-mediated inherited retinal dystrophy. This phase 3 study assessed the efficacy and safety of voretigene neparvovec in participants whose inherited retinal dystrophy would otherwise progress to complete blindness. In this open-label, randomised, controlled phase 3 trial done at two sites in the USA, individuals aged 3 years or older with, in each eye, best corrected visual acuity of 20/60 or worse, or visual field less than 20 degrees in any meridian, or both, with confirmed genetic diagnosis of biallelic RPE65 mutations, sufficient viable retina, and ability to perform standardised multi-luminance mobility testing (MLMT) within the luminance range evaluated, were eligible. Participants were randomly assigned (2:1) to intervention or control using a permuted block design, stratified by age (<10 years and ≥10 years) and baseline mobility testing passing level (pass at ≥125 lux vs <125 lux). Graders assessing primary outcome were masked to treatment group. Intervention was bilateral, subretinal injection of 1·5 × 1011 vector genomes of voretigene neparvovec in 0·3 mL total volume. The primary efficacy endpoint was 1-year change in MLMT performance, measuring functional vision at specified light levels. The intention-to-treat (ITT) and modified ITT populations were included in primary and safety analyses. This trial is registered with ClinicalTrials.gov, number NCT00999609, and enrolment is complete. Between Nov 15, 2012, and Nov 21, 2013, 31 individuals were enrolled and randomly assigned to intervention (n=21) or control (n=10). One participant from each group withdrew after consent, before intervention, leaving an mITT population of 20 intervention and nine control participants. At 1 year, mean bilateral MLMT change score was 1·8 (SD 1·1) light levels in the intervention group versus 0·2 (1·0) in the control group (difference of 1·6, 95% CI 0·72-2·41, p=0·0013). 13 (65%) of 20 intervention participants, but no control participants, passed MLMT at the lowest luminance level tested (1 lux), demonstrating maximum possible improvement. No product-related serious adverse events or deleterious immune responses occurred. Two intervention participants, one with a pre-existing complex seizure disorder and another who experienced oral surgery complications, had serious adverse events unrelated to study participation. Most ocular events were mild in severity. Voretigene neparvovec gene replacement improved functional vision in RPE65-mediated inherited retinal dystrophy previously medically untreatable. Spark Therapeutics.