The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Aldo Badano - One of the best experts on this subject based on the ideXlab platform.
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Method for Adapting the Grayscale Standard Display Function to the Aging Eye
Journal of Digital Imaging, 2017Co-Authors: Giovanni Ramponi, Aldo BadanoAbstract:Perceptual linearity of grayscale images based on a contrast sensitivity model is a widely recognized and used standard for medical imaging visualization. This approach ensures consistency across devices and provides perception of Luminance variations in direct relationship to changes in image values. We analyze the effect of aging of the human eye on the precept of linearity and demonstrate that not only the number of just-noticeable differences diminishes for older subjects but also linearity across the Range of Luminance values is significantly affected. While loss of JNDs is inevitable for a fixed Luminance Range, our findings suggest possible corrective approaches for maintaining linearity.
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SIGGRAPH Posters - GOTHIC: glare optimizer tool for high-dynamic-Range images and content with implementation in video
ACM SIGGRAPH 2013 Posters on - SIGGRAPH '13, 2013Co-Authors: Mina Choi, Luigi Albani, Fahad Zafar, Joel Wang, Gianni Ramponi, Wei-chung Cheng, Aldo BadanoAbstract:Introduction: The Luminance Range of the sun to the night sky is approximately 14 orders of magnitude. Current display technology can present approximately three orders of magnitude, however this number is increasing as High-Dynamic-Range (HDR) technology develops to further emulate reality [Seetzen et al. 2004]. Another benefit to HDR technology is the increased bit-depth enabling the display of more information. However, a major limitation in the perception of added bit-depth is veiling glare. The increased Luminance Range in HDR displays have the ability to produce glare sources that can reduce the visible contrast in neighboring dark areas. This effect is especially undesirable in the visualization of scientific data and in medical images. The HDR presentation must be optimized so that the benefits of a wide Luminance Range are not diminished by glare in the human visual system. One important question is, what is the largest Luminance Range that avoids these veiling glare effects while presenting the most bit-depth? We have found that the answer is highly dependent on the spatial and Luminance distribution in the image. Many models have been proposed to estimate the veiling glare in a given image. A well known model is High-Dynamic-Range Visual Difference Predictor 2 (HDR-VDP-2) [Mantiuk et al. 2011], a calibrated method able to determine the visibility of differences in HDR images. Building on a number of previous metrics of visible difference, this model operates in a broad Range of viewing conditions, from scotopic to photopic vision. More importantly, HDR-VDP-2 can be used to represent the effects of visual glare in signal detection. The inputs of the HDR-VDP-2 are a Luminance map of an image, a reference image, and an image with the target. The software outputs the probability of target detection accounting for various visual effects including veiling glare.
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60.2: Minimizing Veiling Glare in the High‐Luminance‐Range Visualization of Medical Images
SID Symposium Digest of Technical Papers, 2012Co-Authors: Mina Choi, Luigi Albani, Joel Wang, Aldo BadanoAbstract:We propose a method to adjust the Luminance mapping of medical images on high-dynamic-Range (HDR) display devices that minimizes perceptual and hardware veiling glare effects. We utilize the DICOM grayscale standard display function to compute the maximum number of just-noticeable-differences (JND) for an HDR prototype (dual-layer LCD). Using previous findings, a unique image will be displayed with a front and back LCD panel such that the combined light modulation produces the most accurate Luminance representation of the image and the least hardware glare. Next, we use an empirical, image-dependent model to analyze regions of interest in the image that may suffer from perceptual veiling glare and adjust the Luminance mapping until a reasonable degradation tolerance for detection thresholds is reached.
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An image-dependent model of veiling glare effects on detection performance in large-Luminance-Range displays
Medical Imaging 2012: Image Perception Observer Performance and Technology Assessment, 2012Co-Authors: Mina Choi, Luigi Albani, Aldo BadanoAbstract:One limitation of visual detection tasks in complex scenes with a large Range of Luminance values is the decrease in sensitivity due to veiling glare in the display device and in the human eye caused by unwanted light scattering. We used our previously measured results regarding the increase in detection thresholds due to veiling glare to formulate an empirical model for this phenomenon. Our results are based on a ring glare source and a Gaussian target on white noise using a dual-layer, high-dynamic-Range liquid-crystal display prototype. The thresholds, measured using a double-random staircase technique with added signal-absent images, are modeled as a function of ilLuminance at the eyes and angular distance between the veiling glare source and the detection target. In this work, we model increases in detection contrast thresholds due to veiling glare for any image by calculating the contribution of each display pixel. We validate our model by determining threshold increases for the set of experimental results previously obtained with human subjects. Our imagedependent model predicts how the contrast threshold is affected by veiling glare for any target location. Finally, we discuss the Range of validity of our model and show predictions for sample mammography, chest CT, and chest radiography images displayed on large-Luminance-Range devices.
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Display methods for adjustable grayscale and Luminance depth
Medical Imaging 2008: PACS and Imaging Informatics, 2008Co-Authors: Anindita Saha, Giovanni Ramponi, Gabriele Guarnieri, Aldo BadanoAbstract:We explore the calibration of a high Luminance Range, dual-layer, liquid crystal display (LCD) prototype. The operation of the prototype is done by splitting a high Luminance resolution image (graylevel > 2 8 ) into two 8-bit depth components and sending these images to the two liquid crystal panels stacked over the backlight module. By interpolation of a small set of Luminance data gathered using a specialized Luminance probe, the look-up table of graylevel pairs of front/back layer LCD and the corresponding Luminance values can be generated. To display images, we fit an extended DICOM model to the interpolated Luminance table which is adjustable for graylevel and Luminance depth. A dynamic look up table is generated in which for each Luminance there are several graylevel pair candidates. We show results for one possible calibration strategy involving the pair selection criterion. By selecting the pair that maximizes back-layer smoothness, the images with arbitrary graylevel and Luminance depth can be then displayed with equal perceptual distance between Luminance levels, while minimizing parallax effects. Other possible strategies that minimize glare and noise are also described. The results can be used for high Luminance Range display performance characterization and for the evaluation of its clinical significance.
Jiun-haw Lee - One of the best experts on this subject based on the ideXlab platform.
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White Organic Light-Emitting Devices with Ultra-High Color Stability over Wide Luminance Range
Organic Electronics, 2011Co-Authors: Chih-hung Hsiao, Yi-hsin Lan, Pei-yu Lee, Tien-lung Chiu, Jiun-haw LeeAbstract:Abstract A white organic light-emitting device (WOLED) with ultra-high color stability was achieved by introducing an appropriate emitting layer (EML) structure with a spacer, and engineering a blue EML (B-EML) with a selectively doped profile. The advantage of the selectively doped profile over the conventional, uniformly doped profile was to minimize direct exciton formation on dopants with lower exciton energies to suppress electroluminescence (EL) spectrum variations. The recombination zone was found to be located at the spacer/B-EML interface, with a width of 4.5 nm. With the selectively doped profile, the WOLED exhibited ultra-high color stability, with the CIE coordinates shifting from (0.399, 0.483) to (0.395, 0.479) as the Luminance increased from 145 to 12,100 cd/m 2 and from (0.401, 0.481) to (0.400, 0.479) as the Luminance increased from 1240 to 4850 cd/m 2 , the practical Luminance Range for display and lighting applications. In addition to the small CIE coordinates variation of (−0.004, −0.004) over the broad Luminance Range of about two orders of magnitude, we also achieved a high device efficiency of 34.1 cd/A, which stayed larger than 30 cd/A below 2000 cd/m 2 .
Yin Peng - One of the best experts on this subject based on the ideXlab platform.
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spatial adaptive upsampling filter for hdr image based on multiple Luminance Range
Proceedings of SPIE, 2014Co-Authors: Qian Chen, Yin PengAbstract:In this paper, we propose an adaptive upsampling filter to spatially upscale HDR image based on Luminance Range of the HDR picture in each color channel. It first searches for the optimal Luminance Range values to partition an HDR image to three different parts: dark, mid-tone and highlight. Then we derive the optimal set of filter coefficients both vertically and horizontally for each part. When the HDR pixel is within the dark area, we apply one set of filter coefficients to vertically upsample the pixel. If the HDR pixel falls in mid-tone area, we apply another set of filter for vertical upsampling. Otherwise the HDR pixel is in highlight area, another set of filter will be applied for vertical upsampling. Horizontal upsampling will be carried out likewise based on its Luminance. The inherent idea to partition HDR image to different Luminance areas is based on the fact that most HDR images are created from multiple exposures. Different exposures usually demonstrate slight variation in captured signal statistics, such as noise level, subtle misalignment etc. Hence, to group different regions to three Luminance partitions actually helps to eliminate the variation between signals, and to derive optimal filter for each group with signals of lesser variation is certainly more efficient than for the entire HDR image. Experimental results show that the proposed adaptive upsampling filter based on Luminance Ranges outperforms the optimal upsampling filter around 0.57dB for R channel, 0.44dB for G channel and 0.31dB for B channel.
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Digital Photography - Spatial adaptive upsampling filter for HDR image based on multiple Luminance Range
Digital Photography X, 2014Co-Authors: Qian Chen, Yin PengAbstract:In this paper, we propose an adaptive upsampling filter to spatially upscale HDR image based on Luminance Range of the HDR picture in each color channel. It first searches for the optimal Luminance Range values to partition an HDR image to three different parts: dark, mid-tone and highlight. Then we derive the optimal set of filter coefficients both vertically and horizontally for each part. When the HDR pixel is within the dark area, we apply one set of filter coefficients to vertically upsample the pixel. If the HDR pixel falls in mid-tone area, we apply another set of filter for vertical upsampling. Otherwise the HDR pixel is in highlight area, another set of filter will be applied for vertical upsampling. Horizontal upsampling will be carried out likewise based on its Luminance. The inherent idea to partition HDR image to different Luminance areas is based on the fact that most HDR images are created from multiple exposures. Different exposures usually demonstrate slight variation in captured signal statistics, such as noise level, subtle misalignment etc. Hence, to group different regions to three Luminance partitions actually helps to eliminate the variation between signals, and to derive optimal filter for each group with signals of lesser variation is certainly more efficient than for the entire HDR image. Experimental results show that the proposed adaptive upsampling filter based on Luminance Ranges outperforms the optimal upsampling filter around 0.57dB for R channel, 0.44dB for G channel and 0.31dB for B channel.
Chih-hung Hsiao - One of the best experts on this subject based on the ideXlab platform.
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White Organic Light-Emitting Devices with Ultra-High Color Stability over Wide Luminance Range
Organic Electronics, 2011Co-Authors: Chih-hung Hsiao, Yi-hsin Lan, Pei-yu Lee, Tien-lung Chiu, Jiun-haw LeeAbstract:Abstract A white organic light-emitting device (WOLED) with ultra-high color stability was achieved by introducing an appropriate emitting layer (EML) structure with a spacer, and engineering a blue EML (B-EML) with a selectively doped profile. The advantage of the selectively doped profile over the conventional, uniformly doped profile was to minimize direct exciton formation on dopants with lower exciton energies to suppress electroluminescence (EL) spectrum variations. The recombination zone was found to be located at the spacer/B-EML interface, with a width of 4.5 nm. With the selectively doped profile, the WOLED exhibited ultra-high color stability, with the CIE coordinates shifting from (0.399, 0.483) to (0.395, 0.479) as the Luminance increased from 145 to 12,100 cd/m 2 and from (0.401, 0.481) to (0.400, 0.479) as the Luminance increased from 1240 to 4850 cd/m 2 , the practical Luminance Range for display and lighting applications. In addition to the small CIE coordinates variation of (−0.004, −0.004) over the broad Luminance Range of about two orders of magnitude, we also achieved a high device efficiency of 34.1 cd/A, which stayed larger than 30 cd/A below 2000 cd/m 2 .
Patrik Sund - One of the best experts on this subject based on the ideXlab platform.
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[P024] The enlightening of radiologists
Physica Medica, 2018Co-Authors: Patrik SundAbstract:Purpose The working environment for radiologists typically consists of dark rooms in order to increase image contrast. From an ergonomic viewpoint, dark rooms are far from ideal. Darkness is likely to cause fatigue, loss of concentration and thus a potential degradation of diagnostic accuracy. Also, a low screen Luminance requires a rigorously controlled ambient ilLuminance in order to avoid contrast loss due to fluctuating reflections. The purpose of this talk is to examine the scientific reasons for using dark reading rooms. Are they indisputable or do old habits simply die hard? By using state-of-the-art displays – is it possible that an increase in light could also be beneficial to image quality as well as ergonomic conditions? Methods Display contrast was determined by calculating the number of just noticeable differences (jnd) for several display Luminance settings. Since the jnd is based on a limited number of biological processes, effects caused by absolute Luminance level, eye adaptation, Luminance Range and visual acuity were also examined. Results For a constant Luminance ratio, the contrast increased with Luminance. An increase in black level allowed for an increase in ambient light, i.e. less dark reading rooms. By using a high maximum Luminance and a reduced Luminance Range, bright reading rooms could be used without compromising image quality. Unfortunately, most standards and guidelines require a minimum Luminance Range, forcing the maximum Luminance to be higher than technically achievable when increasing the minimum Luminance. A reduced Luminance Range lowers the contrast but can also have positive effects since the human visual system performs better for small differences in Luminance. An increased black level causes the eye to always work in photopic mode where visual acuity is higher and small details are more easily detected. Conclusions With bright medical displays available, it is theoretically possible to use higher Luminance settings in brighter rooms while maintaining – or increasing – image quality. In brighter rooms, radiologists will be able to work in normal office light and relatively large fluctuations in ambient lighting can also be allowed without any significant reductions in image contrast.
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Development and evaluation of a method of calibrating medical displays based on fixed adaptation
Medical physics, 2015Co-Authors: Patrik Sund, Lars Gunnar Månsson, Magnus BåthAbstract:Purpose: The purpose of this work was to develop and evaluate a new method for calibration of medical displays that includes the effect of fixed adaptation and by using equipment and Luminance levels typical for a modern radiology department. Methods: Low contrast sinusoidal test patterns were derived at nine Luminance levels from 2 to 600 cd/m2 and used in a two alternative forced choice observer study, where the adaptation level was fixed at the logarithmic average of 35 cd/m2. The contrast sensitivity at each Luminance level was derived by establishing a linear relationship between the ten pattern contrast levels used at every Luminance level and a detectability index (d′) calculated from the fraction of correct responses. A Gaussian function was fitted to the data and normalized to the adaptation level. The corresponding equation was used in a display calibration method that included the grayscale standard display function (GSDF) but compensated for fixed adaptation. In the evaluation study, the contrast of circular objects with a fixed pixel contrast was displayed using both calibration methods and was rated on a five-grade scale. Results were calculated using a visual grading characteristics method. Error estimations in both observer studies were derived using a bootstrap method. Results: The contrast sensitivities for the darkest and brightest patterns compared to the contrast sensitivity at the adaptation Luminance were 37% and 56%, respectively. The obtained Gaussian fit corresponded well with similar studies. The evaluation study showed a higher degree of equally distributed contrast throughout the Luminance Range with the calibration method compensated for fixed adaptation than for the GSDF. The two lowest scores for the GSDF were obtained for the darkest and brightest patterns. These scores were significantly lower than the lowest score obtained for the compensated GSDF. For the GSDF, the scores for all Luminance levels were statistically separated from the average value; three were lower and two were higher. For the compensated GSDF, three of the scores could not be separated from the average value. Conclusions: An observer study using clinically relevant displays and Luminance settings has demonstrated that the calibration of displays according to the GSDF causes the perceived contrast to be unevenly distributed when using displays with a high Luminance Range. As the Luminance Range increases, the perceived contrast in the dark and bright regions will be significantly lower than the perceived contrast in the middle of the Luminance Range. A new calibration method that includes the effect of fixed adaptation was developed and evaluated in an observer study and was found to distribute the contrast of the display more evenly throughout the grayscale than the GSDF.
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The effect of fixed eye adaptation when using displays with a high Luminance Range
Medical Imaging 2012: Image Perception Observer Performance and Technology Assessment, 2012Co-Authors: Patrik Sund, Lars Gunnar Månsson, Magnus BåthAbstract:Calibration of medical review displays according to the part 14 Grayscale Standard Display Function (GSDF) is important in order to obtain consistency in displayed image quality since display technology and viewing conditions may vary substantially. Unfortunately, the purpose of the GSDF calibration is best suited for low Luminance Range conditions but is not optimal when using modern displays with a high Luminance Range. Low contrast objects will then obtain a greater visibility in mid-gray areas compared to similar objects in bright or dark regions. In this study, low contrast sinusoidal patterns were displayed on a high Luminance Range monitor under realistic viewing conditions. In order to simulate the viewing of an x-ray image with both dark and bright regions displayed simultaneously, the Luminance of the patterns Ranged from 2 to 600 cd/m 2 while the observers were always adapted to the logarithmic average of 35 cd/m 2 . The results show a clear relationship between the patterns deviation from the adaptation Luminance level and the necessary contrast required to detect the pattern. The results also indicate the potential for an improvement in the lowcontrast detectability over a large Luminance Range by adjusting the GSDF for the limited eye adaptation.
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A comparison between 8-bit and 10-bit Luminance resolution when generating low-contrast sinusoidal test pattern on an LCD
Medical Imaging 2007: Image Perception Observer Performance and Technology Assessment, 2007Co-Authors: Patrik Sund, Magnus Båth, Linda Ungsten, Lars Gunnar MånssonAbstract:Radiological images are today mostly displayed on monitors, but much is still unknown regarding the interaction between monitor and viewer. Issues like monitor Luminance Range, calibration, contrast resolution and Luminance distribution need to be addressed further. To perform vision research of high validity to the radiologists, test images should be presented on medical displays. One of the problems has been how to display low contrast patterns in a strictly controlled way. This paper demonstrates how to generate test patterns close to the detection limit on a medical grade display using subpixel modulation. Patterns are generated with both 8-bit and 10-bit monitor input. With this technique, up to 7162 Luminance levels can be displayed and the average separation is approximately 0.08 of a JND (Just Noticeable Difference) on a display with a Luminance Range between 1 and 400 cd/m 2 . These patterns were used in a 2AFC detection task and the detection threshold was found to be 0.75 ± 0.02 of a JND when the adaptation level was the same as the target Luminance (20 cd/m 2 ). This is a reasonable result considering that the magnitude of a JND is based on the method of adjustment rather than on a detection task. When test patterns with a different Luminance than the adaptation level (20 cd/m 2 ) were displayed, the detection thresholds were 1.11 and 1.06 of a JND for target Luminance values 1.8 and 350 cd/m 2 , respectively.
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Calibration of diagnostic monitors: Theoretical determination of optimal Luminance settings
Journal of the Society for Information Display, 2006Co-Authors: Magnus Båth, Patrik Sund, Linda Ungsten, Lars Gunnar MånssonAbstract:— Common practice today is to calibrate diagnostic monitors according to the gray-scale standard display function (GSDF) described in DICOM part 14. However, the GSDF is based on the assumption of variable adaptation of the human-visual system (HVS). It is well known that the HVS adapts to the average quantity of light falling on the retina, so-called fixed adaptation. For the Luminance setting of a monitor, the effect of fixed adaptation is of interest. The wider the Luminance Range of the monitor, the larger the number of available just-noticeable differences (JNDs). However, at the same time, the sensitivity of the HVS to the average contrast change is decreased since it occurs at a Luminance level further away from the adaptation Luminance. A computer program was therefore written which takes the effect of the fixed adaptation into account by determining the number of effective JNDs for a given Luminance setting of a monitor. The probability of detecting each change in presentation value is then calculated from the distribution of effective JNDs. Based on the assumptions implemented in the program, it is shown that for monitors calibrated according to the GSDF, the optimal Luminance setting for visualizing the image information in the best possible way is to use the entire available Luminance Range.
