Showing papers on "Contrast (vision) published in 2008"
TL;DR: All operations are restricted so that they preserve the overall image appearance, lightness range and differences, colour ordering, and spatial details, resulting in perceptually accurate achromatic reproductions of the colour original.
Abstract: This paper presents a quick and simple method for converting complex images and video to perceptually accurate greyscale versions. We use a two-step approach first to globally assign grey values and determine colour ordering, then second, to locally enhance the greyscale to reproduce the original contrast. Our global mapping is image independent and incorporates the Helmholtz-Kohlrausch colour appearance effect for predicting differences between isoluminant colours. Our multiscale local contrast enhancement reintroduces lost discontinuities only in regions that insufficiently represent original chromatic contrast. All operations are restricted so that they preserve the overall image appearance, lightness range and differences, colour ordering, and spatial details, resulting in perceptually accurate achromatic reproductions of the colour original.
169 citations
TL;DR: To investigate amblyopic contrast vision at threshold and above, pedestal-masking (contrast discrimination) experiments with a group of eight strabismic amblyopes using horizontal sinusoidal gratings in monocular, binocular and dichoptic configurations balanced across eye were performed.
140 citations
TL;DR: This work demonstrates that this local contrast can be characterized in terms of a log-normal distribution and shows that the two defining parameters of this model can in turn be expressed in Terms of the minimum speckle size and the extent of the local neighborhood.
Abstract: In describing the first-order properties of laser speckle under polarized illumination conditions, it is almost an article of faith that the contrast is unity. In many processing schemes, however, the contrast defined as the quotient of the standard deviation and the mean is calculated over a localized spatial region. In such cases, this local contrast displays a distribution of values that can depart substantially from unity. Properties of this distribution depend on details of the data acquisition and on the size of the local neighborhood over which the contrast is calculated. We demonstrate that this local contrast can be characterized in terms of a log-normal distribution. Further, we show that the two defining parameters of this model can in turn be expressed in terms of the minimum speckle size and the extent of the local neighborhood. Performance of the model is illustrated with some typical optical coherence tomography data.
136 citations
TL;DR: A proposed scheme for estimating JND (just-noticeable difference) with explicit formulation for image pixels, by summing the effects of the visual thresholds in sub-bands, demonstrates favorable results in noise shaping and perceptual visual distortion gauge for different images, in comparison with the relevant existing JND estimators.
108 citations
Patent•
31 Dec 2008TL;DR: An imaging system consisting of a cell-phone with camera as the detection part of an optical train which includes other components is described in this article, which includes an illumination system to create controlled contrast in the sample.
Abstract: An imaging system consisting of a cell-phone with camera as the detection part of an optical train which includes other components. Optionally, an illumination system to create controlled contrast in the sample. Uses include but are not limited to disease diagnosis, symptom analysis, and post-procedure monitoring, and other applications to humans, animals, and plants.
105 citations
TL;DR: The improved performance with WoB targets with respect to BoW targets is decreased when correcting aberrations, suggesting a role of ocular aberration in the differences in visual performance between contrast polarities.
Abstract: We evaluated the visual benefit of correcting astigmatism and high-order aberrations with adaptive optics (AO) on visual acuity (VA) measured at 7 different luminances (ranging from 0.8 to 50 cd/m(2)) and two contrast polarities (black letters on white background, BoW, and white letters on black background, WoB) on 7 subjects. For the BoW condition, VA increased with background luminance in both natural and AO-corrected conditions, and there was a benefit of AO correction at all luminances (by a factor of 1.29 on average across luminances). For WoB VA increased with foreground luminance but decreased for the highest luminances. In this reversed polarity condition AO correction increased VA by a factor of 1.13 on average and did not produce a visual benefit at high luminances. The improvement of VA (averaged across conditions) was significantly correlated (p = 0.04) with the amount of corrected aberrations (in terms of Strehl ratio). The improved performance with WoB targets with respect to BoW targets is decreased when correcting aberrations, suggesting a role of ocular aberrations in the differences in visual performance between contrast polarities.
99 citations
07 Jul 2008
TL;DR: A new objective non-reference quality metric for the performance of pixel level image fusion is proposed that employs a luminance model that is widely used in visual psychophysics and a new contrast model which correlates better with human visual sensitivity to calculate the similarity between fused image and the sources.
Abstract: A new objective non-reference quality metric for the performance of pixel level image fusion is proposed in this paper. The novel metric employs a luminance model that is widely used in visual psychophysics and a new contrast model which correlates better with human visual sensitivity to calculate the similarity between fused image and the sources. Experiments show that the metric is effective and compliant with subjective evaluations compared with other metrics.
97 citations
TL;DR: AcrySof ReSTOR SN60D3 and ReZoom IOLs provided good visual performance at distance and near under photopic conditions and photopic contrast sensitivity was within the standard normal range in both IOL groups.
Abstract: Purpose To evaluate the optical and visual performance after implantation of refractive or apodized diffractive multifocal intraocular lenses (IOLs). Setting Military Health Service Institute, Warsaw, Poland. Methods Uncorrected distance visual acuity, best distance-corrected visual acuity, best distance-corrected near visual acuity, distance contrast sensitivity under photopic conditions (CSV-1000), residual refractive error, and wavefront aberrations (LADARWave Hartmann-Shack wavefront analyzer) were measured in 23 patients who had bilateral implantation of the AcrySof ReSTOR SN60D3 IOL and 23 patients who had bilateral implantation of the ReZoom IOL…. Results At the 6-month postoperative visit, the mean photopic uncorrected distance acuity was 0.03 ± 0.05 (SD) in the ReSTOR group and 0.02 ± 0.06 logMAR in the ReZoom group (both approximately 20/20) ( P = .569). In all patients, the mean photopic best distance-corrected acuity was 0.00 logMAR (approximately 20/20) and the mean photopic best distance-corrected near acuity at 35 cm was 0.10 logMAR. The photopic contrast sensitivity was within the standard normal range in both IOL groups. The difference in photopic contrast sensitivity between groups was statistically significant ( P P Conclusions AcrySof ReSTOR SN60D3 and ReZoom IOLs provided good visual performance at distance and near under photopic conditions. Optical quality measures were significantly worse in patients with ReZoom IOLs.
93 citations
TL;DR: This study investigated how rod mediated changes in color perception varied as a function of the magnitude of the rod contrast, and found that rod contributions to inferred PC, KC and MC pathway mediated vision were linearly related to the rod incremental contrast.
90 citations
TL;DR: The results of experiments using noise to try to better understand the losses in amblyopia show that the amblyopes' reduced efficiency for detecting signals in noise is explained in part by reduced template efficiency but to a greater extent by increased random internal noise.
Abstract: Amblyopia results in a loss of visual acuity, contrast sensitivity, and position acuity. However, the nature of the neural losses is not yet fully understood. Here we report the results of experiments using noise to try to better understand the losses in amblyopia. Specifically, in one experiment we compared the performance of normal, amblyopic, and ideal observers for detecting a localized signal (a discrete frequency pattern or DFP) in fixed contrast white noise. In a second experiment, we used visibility-scaled noise and varied both the visibility of the noise (from 2 to 20 times the noise detection threshold) and the spatial frequency of the signal. Our results show a loss of efficiency for detection of known signals in noise that increases with the spatial frequency of the signal in observers with amblyopia. To determine whether the loss of efficiency was a consequence of a mismatched template, we derived classification images. We found that although the amblyopic observers' template was shifted to lower spatial frequencies, the shift was insufficient to account for their threshold elevation. Reduced efficiency in the amblyopic visual system may reflect a high level of internal noise, a poorly matched position template, or both. To analyze the type of internal noise we used an "N-pass" technique, in which observers performed the identical experiment N times (where N = 3 or 4). The amount of disagreement between the repeated trials enables us to parse the internal noise into random noise and consistent noise beyond that due to the poorly matched template. Our results show that the amblyopes' reduced efficiency for detecting signals in noise is explained in part by reduced template efficiency but to a greater extent by increased random internal noise. This loss is more or less independent of external noise contrast over a log unit range of external noise.
87 citations
TL;DR: The results suggest that there may be an anomalous visual processing in both the magnocellular and parvocellular pathways that could underlie some deficits in visual function during normal aging.
TL;DR: High-spatial-resolution steady-state MR angiography allowed for better agreement with DSA regarding stenosis grade in patients with arterial disease compared with standard-resolution arterial-phase first-pass MRAngiography.
Abstract: Purpose: To prospectively compare the accuracy of high-spatial-resolution steady-state magnetic resonance (MR) angiography with standard-resolution first-pass MR angiography in the lower extremities, with digital subtraction angiography (DSA) as the reference standard. Materials and Methods: Institutional ethics committee approval and written informed consent were obtained. Twenty-seven patients (16 men, 11 women; mean age, 64.4 years ± 14.8 [standard deviation]; range, 26–87 years) suspected of having or known to have peripheral arterial disease underwent first-pass and steady-state MR angiography and DSA. First-pass and steady-state MR angiography were performed in the same patient in the same session and with the same dose of blood pool contrast agent. The most severe stenosis grade of each evaluated segment was measured; sensitivity, specificity, and positive and negative predictive values were calculated at first-pass and steady-state MR angiography, with DSA as the reference standard. The κ coeffici...
TL;DR: Contrast-enhanced whole-heart coronary MR angiography at 3.0 T demonstrated less acquisition time, higher CNR, and better depiction of coronary segments compared with steady-state free precession coronary MRA at 1.5 T.
Abstract: Objectives:To compare contrast-enhanced whole-heart coronary MR angiography (MRA) at 3.0 T and noncontrast steady-state free precession coronary MRA at 1.5 T in the same volunteers.Materials and Methods:Nine healthy volunteers underwent both coronary MRA using 3D FLASH with slow infusion of MultiHan
TL;DR: This article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 × 4 matrix of 28 classes and demonstrates that smaller sizes, slower speeds, and greater luminance contrast all tend to have similar perceptual effects.
TL;DR: In this article, the authors compared the effect of eye movements on subsequent recall and recognition in two groups thought to differ in baseline degree of hemispheric interaction (individuals who are strongly right-handed (SR) and individuals who are not (nSR).
Abstract: Subjects who make repetitive saccadic eye movements before a memory test subsequently exhibit superior retrieval in comparison with subjects who do not move their eyes. It has been proposed that eye movements enhance retrieval by increasing interaction of the left and right cerebral hemispheres. To test this, we compared the effect of eye movements on subsequent recall (Experiment 1) and recognition (Experiment 2) in two groups thought to differ in baseline degree of hemispheric interaction—individuals who are strongly right-handed (SR) and individuals who are not (nSR). For SR subjects, who naturally may experience less hemispheric interaction than nSR subjects, eye movements enhanced retrieval. In contrast, depending on the measure, eye movements were either inconsequential or even detrimental for nSR subjects. These results partially support the hemispheric interaction account, but demand an amendment to explain the harmful effects of eye movements for nSR individuals.
16 Dec 2008
TL;DR: The knowledge of the imaging geometry is used and an enhancement method for colour retinal images is proposed, with a focus on contrast improvement with no introduction of artifacts, to show marked improvement over existing methods.
Abstract: Retinal images are widely used to manually or automatically detect and diagnose many diseases Due to the complex imaging setup, there is a large luminosity and contrast variability within and across images Here, we use the knowledge of the imaging geometry and propose an enhancement method for colour retinal images, with a focus on contrast improvement with no introduction of artifacts The method uses non-uniform sampling to estimate the degradation and derive a correction factor from a single plane We also propose a scheme for applying the derived correction factor to enhance all the colour planes of a given image The proposed enhancement method has been tested on a publicly available dataset Results show marked improvement over existing methods
TL;DR: Fly visual processing may be matched to commonalities between natural scenes, enabling accurate estimates of velocity largely independent of the particular image used despite a threefold range of contrast.
Abstract: How do animals regulate self-movement despite large variation in the luminance contrast of the environment? Insects are capable of regulating flight speed based on the velocity of image motion, but the mechanisms for this are unclear. The Hassenstein–Reichardt correlator model and elaborations can accurately predict responses of motion detecting neurons under many conditions but fail to explain the apparent lack of spatial pattern and contrast dependence observed in freely flying bees and flies. To investigate this apparent discrepancy, we recorded intracellularly from horizontal-sensitive (HS) motion detecting neurons in the hoverfly while displaying moving images of natural environments. Contrary to results obtained with grating patterns, we show these neurons encode the velocity of natural images largely independently of the particular image used despite a threefold range of contrast. This invariance in response to natural images is observed in both strongly and minimally motion-adapted neurons but is sensitive to artificial manipulations in contrast. Current models of these cells account for some, but not all, of the observed insensitivity to image contrast. We conclude that fly visual processing may be matched to commonalities between natural scenes, enabling accurate estimates of velocity largely independent of the particular scene.
TL;DR: A histogram-based model, derived from exemplars, provides a pragmatic guide for image analysis and enhancement and in AREDS2, the best digital images matched the best film.
Abstract: PURPOSE To analyze brightness, contrast, and color balance of digital versus film retinal images in a multicenter clinical trial, to propose a model image from exemplars, and to optimize both image types for evaluation of age-related macular degeneration (AMD). METHODS The Age-Related Eye Disease Study 2 (AREDS2) is enrolling subjects from 90 clinics, with three quarters of them using digital and one quarter using film cameras. Image brightness (B), contrast (C), and color balance (CB) were measured with three-color luminance histograms. First, the exemplars (film and digital) from expert groups were analyzed, and an AMD-oriented model was constructed. Second, the impact of B/C/CB on the appearance of typical AMD abnormalities was analyzed. Third, B/C/CB in AREDS2 images were compared between film (156 eyes) and digital (605 eyes), and against the model. Fourth, suboptimal images were enhanced by adjusting B/C/CB to bring them into accord with model parameters. RESULTS Exemplar images had similar brightness, contrast, and color balance, supporting an image model. Varying a specimen image through a wide range of B/C/CB revealed greatest contrast of drusen and pigment abnormalities against normal retinal pigment epithelium with the model parameters. AREDS2 digital images were more variable than film, with lower correspondence to our model. Ten percent of digital were too dim and 19% too bright (oversaturated), versus 1% and 4% of film, respectively. On average, digital had lower green channel contrast (giving less retinal detail) than film. Overly red color balance (weaker green) was observed in 23% of digital versus 8% of film. About half of digital (but fewer film) images required enhancement before AMD grading. After optimization of both image types, AREDS2 image quality was judged as good as that in AREDS (all film). CONCLUSIONS A histogram-based model, derived from exemplars, provides a pragmatic guide for image analysis and enhancement. In AREDS2, the best digital images matched the best film. Overall, however, digital provided lower contrast of retinal detail. Digital images taken with higher G-to-R ratio showed better brightness and contrast management. Optimization of images in the multicenter study helps standardize documentation of AMD (ClinicalTrials.gov NCT00345176).
TL;DR: The results obtained indicate that the proposed algorithm exhibits at least comparable results in contrast modification tasks to the other algorithms, in significantly reduced execution times.
Abstract: A new algorithm for fast contrast modification of standard dynamic range (SDR) images (8 bits/ channel) is presented. Its thrust is to enhance the contrast in the under-/over-exposed regions of SDR images, caused by the low dynamic range of the capturing device. It is motivated by the attributes of the shunting centre - surround cells of the human visual system. The main advantage of the proposed algorithm is its O(N ) complexity which results in very fast execution, even when executed on a conventional personal computer (0.2 s/frame for a 640 � 480 pixel resolution on a 3 GHz Pentium 4). Thus, it moderately increases the computational burden if it is used as a pre-processing stage for other image processing algorithms. The proposed method is compared with other established algorithms, which can enhance the contrast in the under-/over-exposed regions of SDR images: the multi-scale Retinex with colour rendition, the McCann Retinex (McCann99), the rational mapping function and the automatic colour equalisation. The results obtained by this comparison indicate that the proposed algorithm exhibits at least comparable results in contrast modification tasks to the other algorithms, in significantly reduced execution times.
TL;DR: This study aims to compare the effects of perceptual learning or patching on improving visual acuity and contrast sensitivity in patients with anisometropic amblyopia.
TL;DR: The results have important implications for the use of Bangerter filters therapeutically, as similar, minimal degradation of distance and near optotype and vernier acuity is caused, whereas subsequent filters cause progressive degradation.
Abstract: Purpose Bangerter filters are designed to cause progressive degradation of distance optotype acuity to predicted levels (density label indicating expected decimal acuity) and are used to treat amblyopia and diplopia. Few authors have reported data regarding induced acuity deficits. We investigated the effect of Bangerter filters on distance and near optotype acuity, vernier acuity, and contrast sensitivity. Methods Fifteen subjects with best-corrected optotype acuity of at least 20/25 in each eye were blurred sequentially in one eye with 7 Bangerter filters (densities Results The 1.0, 0.8, and 0.4 filters degraded distance optotype acuity to a similar degree (mean 0.22, 0.23, and 0.28 logMAR). Subsequent filters progressively degraded acuity: 0.44, 0.57, 0.93, and 1.69 logMAR. Near optotype acuity was reduced in a similar pattern. Vernier acuity was minimally degraded by 1.0, 0.8, and 0.4 filters (18, 19, and 20 arcsec), followed by progressive degradation with subsequent filters (31, 35, 113, and 387 arcsec). Contrast sensitivity was minimally reduced with filters 1.0 through 0.2 and then precipitously degraded with 0.1 and Conclusions The 1.0, 0.8, and 0.4 filters cause similar, minimal degradation of distance and near optotype and vernier acuity, whereas subsequent filters cause progressive degradation. Contrast sensitivity is not markedly reduced until the 0.1 filter. These results have important implications for the use of Bangerter filters therapeutically.
TL;DR: The African mole-rats possess relatively well-developed functional visual subsystems involved in photoperiodicity, form and brightness discrimination, in contrast with surface-dwelling sighted rodents, which suggests the retention of basic visual capabilities.
TL;DR: Findings show that asymmetries in spatial vision are explained by independent retinal and cortical mechanisms.
TL;DR: A new multiresolution wavelet model is presented here, which accounts for brightness assimilation and contrast effects in a unified framework, and includes known psychophysical and physiological attributes of the primate visual system.
TL;DR: Preliminary evidence suggests NVC treatment is safe and improves UCVA and uncorrected contrast sensitivity in adult patients with low myopia.
Abstract: Purpose To evaluate the efficacy and safety of neural vision enhancement technology (NVC, NeuroVision, Inc.) to improve visual acuity and contrast sensitivity function in eyes with low myopia. Setting Singapore Eye Research Institute, Singapore, Singapore. Methods This noncomparative interventional case series comprised 20 Asian adults between 19 and 53 years of age with low myopia (cycloplegic spherical equivalence [SE] from −0.5 diopter [D] to −1.5 D in the worst eye; astigmatism not exceeding 0.5 D in either eye; uncorrected visual acuity [UCVA] ≤0.7 logMAR) who had NVC treatment. The main outcome measures were distance UCVA, uncorrected contrast sensitivity, refraction, accommodative amplitude, and safety. Results All eyes had improvement in UCVA and contrast sensitivity. After treatment, the mean distance UCVA improved by a mean of 2.1 lines on the Early Treatment Diabetic Retinopathy Study logMAR chart. The mean contrast sensitivity improved over a range of spatial frequencies on sine-wave contrast sensitivity chart testing (1.5 to 18 cycles per degree). Follow-up data up to 12 months posttreatment showed that the gains were retained. Treatment did not alter refraction (mean spherical equivalent) or accommodative amplitudes. No adverse effects were reported. Conclusion Preliminary evidence suggests NVC treatment is safe and improves UCVA and uncorrected contrast sensitivity in adult patients with low myopia.
14 Dec 2008
TL;DR: Quantitatively evaluate contrast flow level selectivity noted during fluoroscopically guided lumbosacral transforaminal epidural steroid injections to identify the minimum injectate volume at which LS-TFESIs may still be considered "selective" with no injectate extending to either the adjacent levels or to the contralateral side.
TL;DR: The analysis of influence of polarity on legibility showed that, generally, dark backgrounds lead to better results for colors with greatest luminance contrast, and that more than 90-year-old Le Courier legibility table is not appropriate for integrative color computer displays.
TL;DR: Parrots opened their pupils at higher light levels than owls, which correlates with the differences in sensitivity between diurnal and nocturnal eyes, and the results suggest that parrots may use a similar mechanism to compensate for longitudinal chromatic aberration.
Abstract: In animal eyes of the camera type longitudinal chromatic aberration causes defocus that is particularly severe in species with short depth of focus. In a variety of vertebrates, multifocal optical systems compensate for longitudinal chromatic aberration by concentric zones of different refractive powers. Since a constricting circular pupil blocks peripheral zones, eyes with multifocal optical systems often have slit pupils that allow light to pass through all zones, irrespective of the state of pupil constriction. Birds have circular pupils and were therefore assumed to have monofocal optical systems. We examined the eyes of 45 species (12 orders) of bird using videorefractometry, and the results are surprising: 29 species (10 orders) have multifocal systems, and only five species (five orders) have monofocal systems. The results from 11 species (four orders) are inconclusive. We propose that pupils ;switching' between being fully opened (multifocal principle) to maximally closed (pinhole principle) can make multifocal optical systems useful for animals with circular pupils. Previous results indicate that mice have both multifocal optical systems and switching pupils. Our results suggest that parrots may use a similar mechanism. By contrast, owl pupils responded weakly to changes in illumination and stayed remarkably wide even in full daylight. Moreover, the parrots opened their pupils at higher light levels than owls, which correlates with the differences in sensitivity between diurnal and nocturnal eyes.
TL;DR: Binocular summation and maximum disparity significantly decrease with increasing interocular differences in higher-order aberrations (total, coma, and spherical aberration).
Abstract: PURPOSE: To analyze the influence of higher-order aberrations on binocular visual performance under mesopic conditions. METHODS: We measured aberrations in both eyes of 35 emmetropic observers with a Wasca aberrometer. Binocular visual performance was checked with both binocular summation for contrast sensitivity function and a parameter that characterizes stereopsis (maximum disparity). RESULTS: Binocular summation and maximum disparity significantly decrease with increasing interocular differences in higher-order aberrations (total, coma, and spherical aberration). CONCLUSIONS: At least some aspects of binocular visual performance are less effective for large interocular differences in higher-order eye aberrations.
TL;DR: In this paper, the effects of higher-order ocular aberrations on functional visual performance were assessed for seven young healthy subjects, as a function of light level, using a visual simulator incorporating an adaptive optics system.
Abstract: The effects of higher-order ocular aberrations on functional visual performance were assessed for seven young healthy subjects, as a function of light level. Contrast acuity thresholds were measured for a functional vision test with and without correction of higher-order aberrations and at a number of different pupil sizes in three of the subjects investigated. A visual simulator incorporating an adaptive optics (AO) system was used for this purpose. The results show that when light level is decreased, the drop in neural contrast sensitivity limits the impact that increased optical degradations have on vision. The expected AO benefit for functional vision is given for scotopic, mesopic and photopic regimes.