Visibility Threshold Research Articles

Conversion of Analog TV Translators for DTV Operation

There are approximately 4700 TV translators in use today across the US and it is estimated that about 7-10 Million households receive their broadcast coverage through the use of these translators. As the transition to digital occurs, it will require the conversion of the existing analog translators to digital or the purchase of new digital translators. Where possible, the FCC has indicated that it is desired to add digital translator channels to co-exist with analog translators. In cases where new channels are not available, the more economic scenario to provide digital signal coverage is to convert the existing analog translators to digital operation (assuming the desired coverage and technical performance can be met) rather than purchase new equipment. This paper examines existing analog translator block diagrams and identifies areas of significant concern and/or weak links in the reception/transmission path. Guidelines for minimum performance levels for various portions of the RF block diagram are identified in order to meet a given Signal to Noise Ratio (SNR) level at the translator output. Typical low power translators of solid state design are characterized for DTV performance using modern test equipment. The amplitude and group delay performance of an analog receiver IF filter is examined to determine whether it is suitable for 8-VSB digital signals that are more spectrum efficient. Information on expected performance from heterodyne and demodulation/re-modulation (regenerative) translator configurations is presented with respect to impact on SNR and out-of-band emissions. A two-hop translator system is analyzed to view the impact of cascading distortions and some qualitative information is presented. Specific calculations are provided for adjacent channel scenarios. Specific measurements are made assuming a situation of equal power level incoming adjacent channel interference to determine the level of energy passed through a heterodyne translator. The measured results of typical analog translators converted to digital operation are used to evaluate a hypothetical site consisting of the converted analog translator that is co-located with analog transmitters occupying both adjacent channels. Associated digital power output levels are determined using Threshold of Visibility and Audibility (TOV and TOA) limits.

Just noticeable distortion model and its applications in video coding

We explore a new perceptually-adaptive video coding (PVC) scheme for hybrid video compression, in order to achieve better perceptual coding quality and operational efficiency. A new just noticeable distortion (JND) estimator for color video is first devised in the image domain. How to efficiently integrate masking effects together is a key issue of JND modelling. We integrate spatial masking factors with the nonlinear additivity model for masking (NAMM). The JND estimator applies to all color components and accounts for the compound impact of luminance masking, texture masking and temporal masking. Extensive subjective viewing confirms that it is capable of determining a more accurate visibility threshold that is close to the actual JND bound in human eyes. Secondly, the image-domain JND profile is incorporated into hybrid video encoding via the JND-adaptive motion estimation and residue filtering process. The scheme works with any prevalent video coding standards and various motion estimation strategies. To demonstrate the effectiveness of the proposed scheme, it has been implemented in the MPEG-2 TM5 coder and demonstrated to achieve average improvement of over 18% in motion estimation efficiency, 0.6 dB in average peak signal-to perceptual-noise ratio (PSPNR) and most remarkably, 0.17 dB in the objective coding quality measure (PSNR) on average. Theoretical explanation is presented for the improvement on the objective coding quality measure. With the JND-based motion estimation and residue filtering process, hybrid video encoding can be more efficient and the use of bits is optimized for visual quality.

Enhanced-xVSB system development for mobile/portable reception

This paper describes the advanced dual stream system for improving mobile/pedestrian reception performance to the ATSC DTV 8-VSB transmission standard. The proposed system can transmit a mixture of normal (8-VSB) stream and enhanced (robust) stream. The robust stream has a lower threshold of visibility (TOV) compared to the standard stream, and legacy receivers ignore the robust packets. Thus, the enhanced-xVSB system is fully backward compatible with a current ATSC standard. For more robust transmission support, E-xVSB system adopts a reduced constellation method as well as enhanced trellis-coded modulation scheme. E-xVSB system supports a variety of enhanced modulation schemes: pseudo-2VSB, enhanced-4VSB, modified enhanced-8VSB and hybrid-VSB. The proposed system has been tested in the lab, and the testing results are shown in this paper.

Improved estimation for just-noticeable visual distortion

Perceptual visibility threshold estimation, based upon characteristics of the human visual system (HVS), has wide applications in digital image/video processing. An improved scheme for estimating just-noticeable distortion (JND) is proposed in this paper. It is proved to outperform the DCTune model, with the major contributions of a new formula for luminance adaptation adjustment and the incorporation of block classification for contrast masking. The HVS visibility threshold for digital images exhibits an approximately parabolic curve versus gray levels and this has been formulated to yield a more accurate base threshold. Moreover, edge regions have been differentiated via block classification to effectively avoid over-estimation of JND in the said regions. Experiments with different images and the associated subjective tests show improved performance of the proposed scheme over the DCTune model for luminance adaptation (especially in dark regions) and masking effect in edge regions. Our model has further demonstrated to achieve favorable results in perceptual visual distortion gauge and image compression. The improvement in JND estimation facilitates better visual distortion measurement and visual signal compression.

As the Saint Turns: Hagiograpy at the Threshold of the Visible

As the Saint Turns: Hagiograpy at the Threshold of the Visible

P-32: How Visible are Defective Pixels in High-Resolution Displays?

We determined the luminance level at which a defective pixel in a relatively dark environment becomes visible as a function of its visual angle, its color and the average display background luminance. A new model has been implemented that can predict these visibility thresholds. The results can be used to update the ISO standard for the acceptability of defective pixels in high-resolution displays.

Visibility threshold in sharpness for people with different regional backgrounds

Abstract— The influence of regional background on the visibility of sharpness differences has been investigated by blurring various still images to different extents. The assessment of sharpness has been performed both in China by Chinese people and in the Netherlands by European people. The results showed that both Chinese characters and Roman text were clearly more critical image material for judging sharpness than natural images. Independent on whether the image contained Chinese characters or Roman text, the visibility threshold for a difference in sharpness was the same for both the Chinese and European people. When related to a diagonal step response, the threshold on average equaled an angular resolution of 5 arcsec.

Sub-50-fs laser retinal damage thresholds in primate eyes with group velocity dispersion, self-focusing and low-density plasmas.

In vivo retinal injury studies using sub-50-femtosecond laser pulses in the near-infrared must consider nonlinear effects such as group velocity dispersion (GVD), self-focusing, laser-induced breakdown (LIB) and low-density plasmas (LDPs). In this paper we present the results of our theoretical calculations of nonlinear effects and our experimental measurements for the visible lesion thresholds in live eyes. We compare these values with the measured LIB and LDP thresholds in an artificial eye. All three thresholds were measured with and without pre-chirping the input pulse to compensate for GVD effects. We recorded the minimum visible lesion (MVL) thresholds in vivo for sub-50-fs laser pulses, with and without pre-chirping the input pulses. In addition, we measured the LIB and LDP thresholds, with and without pre-chirping, within an artificial eye. Different degrees of pre-chirping were required to give optimal compensation for GVD in the live eye and the artificial eye. Probit analysis was used on all data, and comparisons among thresholds were made, to determine the effects on the three thresholds of chirp compensation for GVD. Results of our nonlinear modeling and calculations for GVD compensation, self-focusing, LIB, and low-density plasmas were compared with our experimental results using live eyes and the artificial eye. The damage threshold in live eyes dropped in energy from 0.25 microJ, for the flat-phase input, to 0.17 microJ when optimally chirped pulses were used, while the LIB threshold was reduced from 0.29 microJ to 0.19 microJ with optimally chirped pulses. The LDP threshold dropped from 0.21 microJ to 0.14 microJ with the pre-chirped pulse. At 44 fs, these energies produced peak powers at least twice the calculated critical power that produces nonlinear self-focusing and beam collapse, for propagation of non-aberrated gaussian beams in a uniform medium. Based on our measurements of the MVL thresholds, with and without GVD compensation, we conclude that the visible lesion thresholds produced by 44 fs pulses in rhesus eyes are increased in energy due to GVD. The MVL ED50 was reduced by one third when the pulse was pre-chirped to compensate for GVD in the eye. This reduction in amplitude also holds true in the artificial eye for the LIB ED50 bubble thresholds and the LDP ED50 plasma channels, when using pre-chirped pulses versus non-chirped pulses. We also conclude from the data presented that low-density plasmas, and not LIB cavitation bubbles, are the probable mediating factor at the visible lesion thresholds observed within live eyes, for pulse durations at and below 50 fs. Therefore, the plasma channel created by LDPs is the major damage mechanism, if not the only damage mechanism, at MVL threshold energies for these pulse durations.

Subthreshold Transpupillary Thermotherapy Reduces Experimental Choroidal Neovascularization in the Mouse without Collateral Damage to the Neural Retina

Transpupillary thermotherapy (TTT) is currently being evaluated for treatment of choroidal neovascularization (CNV) in age-related macular degeneration. To optimize TTT for CNV, the effect was analyzed of invisible (subthreshold) or visible (threshold) doses of TTT on the normal mouse retina and on experimental CNV. TTT was delivered to the normal retina of 42 mice with a diode laser at increasing power settings (50, 60, 70, or 80 mW), to obtain thermal lesions ranging from invisible (subthreshold) to visible (threshold) burns. CNV was induced in 53 mice by krypton laser photocoagulation of the fundus, after which the CNV lesions were treated with TTT (50, 60, or 80 mW). Eyes were enucleated 7 days after TTT and prepared for histology, and the CNV complex was evaluated on hematoxylin-eosin stained serial sections by measuring the maximum height of the CNV lesions. Ultrastructural changes were examined by transmission electron microscopy. Increasing the TTT laser power yielded gradually more visible effects. At 50 mW, which induced subthreshold burns, no damage was seen in the neural retina, retinal pigment epithelium (RPE), or choroid at any time point. By contrast, eyes treated with higher power exhibited progressively more damage to the neural retina, including a complete disruption of the outer nuclear layer. When TTT was applied to the laser-induced CNV lesions, the height of lesions was significantly reduced (P < 0.001) in response to all three power settings at 7 days after treatment. The mean relative thickness of the CNV lesion was 3.29 +/- 0.89 in untreated mice, whereas in TTT-treated mice it was 1.69 +/- 0.35, 1.69 +/- 0.41 and 1.70 +/- 0.17 at power settings of 50, 60, and 80 mW, respectively. The overlying neural retina showed no apparent damage with the 50- or 60-mW settings, whereas outer nuclear layer disruption occurred with a power of 80 mW. Electron microscopy confirmed the presence of vascular occlusion at 1 day and a fibrotic scar at 7 days after TTT. Subthreshold TTT can effectively occlude newly formed vessels and cause regression of the experimental CNV complex without damaging the neural retina. The results demonstrate the importance of using subthreshold laser power in experimental and clinical evaluation of TTT.

ATSC Terrestrial Digital Television Broadcasting Using Single Frequency Networks

In this paper, we propose an efficient method to broadcast digital television signals using single frequency networks (SFNs) within the Advanced Television Systems Committee (ATSC) transmission systems. In implementing the SFNs of an 8-vestigial side band (8-VSB) Digital Television (DTV) system, the ambiguity problem of the trellis coder is unavoidable in a conventional ATSC transmission system. We propose a memory initialization of the trellis coder to resolve this ambiguity problem. Since the proposed scheme to synchronize multiple transmitters minimizes the changes from the conventional ATSC system, the hardware complexity for these changes is very low. Our simulation results show that the proposed scheme makes a less than 0.1 dB degradation at the threshold of visibility with a bit error rate of 3×10−6 in the additive white Gaussian noise (AWGN) channel. It is possible to reduce the performance degradation by increasing the initialization period of the proposed scheme.

Influence of pulse duration and pulse number in selective RPE laser treatment.

The therapeutic effect of laser treatment for macular diseases is related to the damage to the retinal pigment epithelium (RPE) and the subsequent restoration of the defect due to RPE proliferation. In contrast to conventional laser treatment, it is possible to damage the RPE selectively and to spare the photoreceptors by using repetitive microsecond laser pulses. It was the aim of the study to investigate the influence of pulse duration and number of pulses on angiographically and ophthalmoscopically visible retinal damage thresholds in order to optimize treatment modalities. In total, 625 laser lesions with various parameters were applied to the retina in 11 eyes of 6 Chinchilla breed rabbits using an experimental laser system (Nd:YLF at 527 nm). Pulse duration (1.7 microseconds and 200 nanoseconds) and number of pulses (100, 10, and 1 pulses) were varied at a constant repetition rate of 100 Hz. Damage thresholds were determined in terms of ophthalmoscopic and fluorescein angiographic visibility, and the therapeutic window (TW; angiographic ED(50) vs. ophthalmoscopic ED(50)) as well as the safety range (SR; angiographic ED(84) vs. ophthalmoscopic ED(16)) between both thresholds were calculated. Selected laser lesions were evaluated by histology. Generally, the ED(50) radiant exposure for angiographic visibility decreases for shorter laser pulses and with an increase in the number of pulses. The TW for both pulse durations (1.7 microseconds and 200 nanoseconds) was wider with 100 pulses than with single pulses. The widest TW was found for 100 pulses at 200 nanoseconds pulse duration (5.9-fold above the angiographic threshold), and the smallest TW with a factor of 1.6 was found for 1.7 microseconds single pulses. In terms of SR, only irradiation with 100 pulses at 200 nanoseconds pulse duration was associated with a ratio >2. Independently of pulse duration, histological examination of laser sites 1 hour after irradiation revealed widely intact photoreceptors, while the underlying RPE was damaged. Pulse duration and number of pulses have a significant influence on RPE damage thresholds and consecutively on TW and SR. Because fundus pigmentation in humans may vary intra- and interindividually by a factor of 2, a large TW and ideally also a large SR should be ensured in a clinical treatment context. In rabbits, the safety range with 200 nanoseconds pulses is higher than with the pulse duration of 1.7 microseconds currently in clinical use. These findings suggest the need for clinical pilot studies to prove whether these results can be transposed to the situation in humans.

A newly proposed ATSC DTV system for transmitting a robust bit-stream along with the standard bit-stream

This paper describes the proposed improvements to the ATSC DTV standard. The proposed system provides a mechanism for embedding a new robust bit-stream in the standard bit-stream in a backward compatible manner. The robust stream has a higher threshold of visibility (TOV) compared to the standard stream and can be transmitted either in the pseudo 2-VSB mode or in the enhanced-coded 8-VSB (E-VSB) mode. A prototype transceiver system, based on the proposed system, has been developed and was tested in the lab and in the field. The results of these tests will be briefly reviewed in this paper.

19.1: The Visibility of a Global Luminance Profile of a Display

AbstractThe visibility threshold of a global luminance profile of a display has been determined with and without an undistorted display as a reference and for both a black and silver‐grayish color of the bezel frame. Results indicate a significant effect of the color of the bezel frame and a dependence on image content. For natural images, the visibility threshold is significantly lower with than without a reference, especially for those profiles, which are darker in the center than near the edges.

19.2: The Visibility of a Local Deviation in Luminance and White‐Point of a Display

AbstractThe visibility threshold of a Gaussian deviation in the luminance or the white‐point of a display has been determined. In the most critical situation, i.e. for homogeneous and moving images, the threshold corresponds to a ΔE*uv of about 1 in the case of a local luminance variation and a ΔE*uv of about 2.5 in the case of a local variation in the white‐point.

Clover as a tool for bioindication of phytotoxic ozone—5 years of experience from southern Sweden—consequences for the short-term critical levels

Critical levels (CLs) for ozone effects on plants in Europe have been defined within the UN-ECE Convention on Long-Range Transboundary Air Pollution, CLRTAP. The purpose of the short-term CLs is to ensure protection of all crops to acute ozone injury. The currently used CLs are based on the ozone exposure of the plants during daylight hours expressed as AOT40 (Accumulated exposure Over the Threshold 40 nmol mol −1 ozone). The aims of this study were: to test the performance of the current short-term CLs, to test alternative ozone exposure indices and to test if changes in the ozone cut-off concentration, the inclusion of a lag-period (LP) between exposure and identification of visible ozone injury or the duration of the ozone integration period improved the performance of the exposure index. The analysis was based on 38 different datasets from experiments with subterranean clover, Trifolium subterraneum in southern Sweden. AOT indices generally performed better than averaged ozone concentrations or SUM (Sum of ozone concentrations when a threshold is exceeded) indices. Regression analysis showed that the current short-term CL, AOT40 with a VPD (water vapour pressure deficit) threshold of 1.5 kPa, explained 56% of the variation in visible injury. A longer exposure period and the introduction of a LP, admitting visible ozone injury time to develop after exposure, improved the performance of the exposure index. AOT30 accumulated over 10 days before harvest, excluding a LP of 3 days before injury observation, performed best and explained 88% of the variation in visible injury. AOT40 indices left a rather large amount of visible injury unexplained indicating that a lower cut-off concentration for ozone is preferable. The results of the investigation indicated that a visible injury threshold of 10% improved the distinction between harmful and less harmful exposure.

Visibility Effectiveness of Hemisphere and Corner Cube Retroreflective Pavement Markers on Curved Roads

This study was conducted to investigate the visibility effectiveness of hemisphere and corner cube pavement markers on various curved road driving conditions. The study consisted of a field experiment to investigate visual threshold and an evaluation study to investigate visibility effectiveness. In the field experiment, a U-shaped test track with a curvature of 30 m radius was set up to investigate the visibility threshold. Two marker types, the hemisphere and the corner cube, and two directional driving conditions, right-turn and left-turn conditions, were considered. The results indicate that there is no difference between marker types, but there are differences between turning directions. The left turn has a significantly higher value and is therefore determined to be the resultant visual threshold. The resultant visual threshold is 1.70×10-6lx, and this is significantly higher than the recommendation of the Commission Internationale de l’Eclairage (CIE). The evaluation study was to evaluate the visibility effectiveness of these two markers on eight curved roads with different radii based on the resultant visual threshold. The evaluation indicates that both pavement markers meet the 3 s preview time as suggested by CIE. However, it also suggests that the corner cube is superior on roads with radii greater than 60 m, whereas the hemisphere is much better for the roads with radii smaller than 60 m.

We are not at Home: Protecting Domestic Privacy in Post-Fire Middle-Class London

This article explores the attitudes of mainly middle-class post-Fire Londoners towards domestic privacy, focussing on the visible and invisible thresholds setting private space apart. It presents a reconstruction of the complex interplay between material structures, patterns of behaviour and evolving mentalities, all of which were in a state of flux before they settled into new, widely received concepts of middle-class normality.It identifies key changes in London's domestic architecture which took place after the Great Fire. As the pre-modern nexus between spatial proximity and social cohesion was broken, new ideas about privacy arose which were translated into both bricks-and-mortar structures and patterns of behaviour. Domestic privacy was not only protected by means of material thresholds, but also by a new protocol of polite visiting. Visits became stage-managed performances: an edited version of private life was acted out before one's visitors while intimate nuclei of privacy remained securely hidden away. Interior domestic spaces were refashioned following a tripartite division (rooms used by servants, rooms inhabited by members of the family and rooms which were made accessible to visitors). This type of arrangement guaranteed an adequate protection of areas designated as private space. At the same time, notions of gender roles changed along with a clearer separation of domestic space into female and male areas. Domestic space became private in that intruders could be excluded from it at will. However, the system of multiple thresholds which protected the private home was by no means impenetrable; its most characteristic feature was its selective permeability.

Using Perceptual Texture Masking for Efficient Image Synthesis

Texture mapping has become indispensable in image synthesis as an inexpensive source of rich visual detail. Less obvious, but just as useful, is its ability to mask image errors due to inaccuracies in geometry or lighting. This ability can be used to substantially accelerate rendering by eliminating computations when the resulting errors will be perceptually insignificant. Our new method precomputes the masking ability of textures using aspects of the JPEG image compression standard. This extra information is stored as threshold elevation factors in the texture's mip-map and interpolated at image generation time as part of the normal texture lookup process. Any algorithm which uses error tolerances or visibility thresholds can then take advantage of texture masking. Applications to adaptive shadow testing, irradiance caching, and path tracing are demonstrated. Unlike prior methods, our approach does not require that initial images be computed before masking can be exploited and incurs only negligible runtime computational overhead. Thus, it is much easier to integrate with existing rendering systems for both static and dynamic scenes and yields computational savings even when only small amounts of texture masking are present. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Color, shading, shadowing, and texture

Thresholds for retinal injury from multiple near-infrared ultrashort laser pulses.

Multiple-pulse lasers are routinely used in the laboratory for research, manufacturing, medical procedures, and in military applications. In order to provide a safe work environment for personnel using these lasers, safety standards have been established and have been in use for many years. These safety standards have addressed laser pulses of nanosecond duration and longer. Recently, safety standards have been updated to address laser pulses as short as 100 femtoseconds in duration. In order to tie these "ultrashort" laser pulses to hazard trends in currently established standards for multiple-pulse exposures with repetition rates less than several kilohertz, this experiment was conducted. Reported herein are minimum visible lesion thresholds in the paramacula of the primate retina using an 800-nm wavelength laser with 1,000 pulses per second, at 130 femtoseconds (fs) pulse duration. The minimum visible lesion (MVL) thresholds were determined at 1 h and 24 h post exposure for 1, 10, 100, 1,000, and 10,000 pulses and are compared with thresholds reported by other researchers. These new data are evaluated relative to the current safety standards for retinal exposure limits as a function of the number of pulses for femtosecond-pulse duration. Data from this study show that the retinal ED50 thresholds/pulse in the paramacula decrease by almost a factor of four as the number of pulses goes from one to ten and then decrease very little for an increase of three decades more in the number of pulses. The MVL-ED50 at the threshold decreased from 0.55 microJ for a single pulse to 0.15 microJ/pulse for 10 pulses and then only to 0.11 microJ/pulse for 10,000 pulses.

23.2: The Visibility of a Color Gradient Across the Screen for Stimuli Presented Time‐Sequentially or Simultaneously

AbstractThe visibility threshold of a color gradient across the screen is determined for the specific application of mobile displays. The color gradient was implemented as a change in saturation or in hue from the center of the screen towards the edges in horizontal direction. Its visibility threshold is determined in a double‐stimulus subjective test. To investigate the influence of the way stimuli are presented in this type of tests, each pair of stimuli is shown twice to the subjects: once with the two stimuli of the pair simultaneously, and once with the two stimuli of the pair time‐sequentially. The results exhibit a remarkable difference in the effect of the way stimuli are presented between the visibility in a saturation gradient and in a hue gradient.