Showing papers on "Contrast (vision) published in 2010"

Enhancing the low quality images using Unsupervised Colour Correction Method

Abstract: Underwater images are affected by reduced contrast and non-uniform colour cast due to the absorption and scattering of light in the aquatic environment. This affects the quality and reliability of image processing and therefore colour correction is a necessary pre-processing stage. In this paper, we propose an Unsupervised Colour Correction Method (UCM) for underwater image enhancement. UCM is based on colour balancing, contrast correction of RGB colour model and contrast correction of HSI colour model. Firstly, the colour cast is reduced by equalizing the colour values. Secondly, an enhancement to a contrast correction method is applied to increase the Red colour by stretching red histogram towards the maximum (i.e., right side), similarly the Blue colour is reduced by stretching the blue histogram towards the minimum (i.e., left side). Thirdly, the Saturation and Intensity components of the HSI colour model have been applied for contrast correction to increase the true colour using Saturation and to address the illumination problem through Intensity. We compare our results with three well known methods, namely Gray World, White Patch and Histogram Equalisation using Adobe Photoshop. The proposed method has produced better results than the existing methods.

Noninvasive Visualization and Analysis of Parafoveal Capillaries in Humans

Abstract: The retina is one of the most metabolically active tissues in the human body, and as such, is coupled with a unique system of blood vessels. The inner retinal microvasculature has been mapped out in high resolution using excised monkey retinas.1 Far from the fovea, the capillary network is multi-layered; closer to the fovea, the network thins down to two layers in the peri- to parafoveal region, and to one layer in the immediate parafoveal region. Finally, in the fovea, there are no vessels, forming the foveal avascular zone (FAZ). The average diameter of a normal FAZ as described in textbooks is around 400 to 500 μm. However, there is considerable individual variation.2 The FAZ has been well characterized and is of important clinical significance in a number of different diseases, including diabetes.3 There are two key challenges that must be addressed when performing optical imaging of the retinal microcirculation: low capillary contrast and aberrations in the eye. Contrast is typically improved using a contrast agent, such as in fluorescein angiography (FA). Although FA is considered to be a “gold standard” for studying retinal vessels, it does carry a small risk for adverse reactions.4 Due to these risks, FA is not performed on normal eyes, except under special circumstances. Moreover, FA may not be able to reliably identify the smallest capillaries.5 An alternate method to improve capillary contrast is to use video processing tools based on flow visualization.6 These tools included mean, variance, min, max, range, and transition images. The variance image has been previously applied as a method for increasing vessel contrast in microvessels before applying leukocyte tracking algorithms.7 However, the variance image alone fails to increase the contrast of vessels in our datasets. We will demonstrate that spatial and temporal information can be used to increase the local contrast for moving objects, and enable the visualization of capillaries. Aberrations in the eye, which may hinder the resolution of the smallest capillaries (i.e., those with diameter ∼5 μm), can be corrected using adaptive optics.8 Recently, an adaptive optics scanning laser ophthalmoscope (AOSLO) was used to quantify leukocyte speeds through parafoveal capillaries.9,10 In this article, we will combine video and image processing tools with AOSLO imaging to demonstrate an improved method that can detect even the smallest capillaries in the parafoveal region without the use of injected dyes.

Novel image-enhanced endoscopy with i-scan technology.

Abstract: i-scan technology is the newly developed image-enhanced endoscopy technology from PENTAX, Japan. This consists of three types of algorithms: surface enhancement (SE), contrast enhancement (CE), and tone enhancement (TE). SE enhances light-dark contrast by obtaining luminance intensity data for each pixel and applying an algorithm that allows detailed observation of a mucosal surface structure. CE digitally adds blue color in relatively dark areas, by obtaining luminance intensity data for each pixel and applying an algorithm that allows detailed observation of subtle irregularities around the surface. Both enhancement functions work in real time without impairing the original color of the organ, therefore, SE and CE are suitable for screening endoscopy to detect gastrointestinal tumors at an early stage. TE dissects and analyzes the individual RGB components of a normal image. The algorithm then alters the color frequencies of each component and recombines the components to a single, new color image. This is designed to enhance minute mucosal structures and subtle changes in color. TE works in real time and consists of three modes such as TE-g for gastric tumors, TE-c for colonic tumors, and TE-e for esophageal tumors. TE is suitable mainly for detailed examination of the lesions that are detected in a screening endoscopy. i-scan technology leads us to easier detection, diagnosis and treatment of gastrointestinal diseases.

4D phase contrast MRI at 3 T: effect of standard and blood-pool contrast agents on SNR, PC-MRA, and blood flow visualization.

Abstract: Time-resolved phase contrast (PC) MRI with velocity encoding in three directions (flow-sensitive four-dimensional MRI) can be employed to assess three-dimensional blood flow in the entire aortic lumen within a single measurement. These data can be used not only for the visualization of blood flow but also to derive additional information on vascular geometry with three-dimensional PC MR angiography (MRA). As PC-MRA is sensitive to available signal-to-noise ratio, standard and novel blood pool contrast agents may help to enhance PC-MRA image quality. In a group of 30 healthy volunteers, the influence of different contrast agents on vascular signal-to-noise ratio, PC-MRA quality, and subsequent three-dimensional stream-line visualization in the thoracic aorta was determined. Flow-sensitive four-dimensional MRI data acquired with contrast agent provided significantly improved signal-to-noise ratio in magnitude data and noise reduction in velocity data compared to measurements without contrast media. The agreement of three-dimensional PC-MRA with reference standard contrast-enhanced MRA was good for both contrast agents, with improved PC-MRA performance for blood pool contrast agent, particularly for the smaller supra-aortic branches. For three-dimensional flow visualization, a trend toward improved results for the data with contrast agent was observed.

Visual Discomfort and Natural Image Statistics

Abstract: Images with excessive energy at medium spatial frequencies (Fernandez and Wilkins 2008), or that have high color contrast and little or no luminance contrast (Wilkins et al 2008) appear uncomfortable or aversive and can induce headaches in hypersensitive observers. Such stimuli are uncharacteristic of natural images, and we examined whether visual discomfort more generally increases with deviations from the spatial and chromatic properties of natural scenes. Observers rated the level of discomfort or artistic merit in color images generated from noise or random overlapping rectangles (Mondrians). In one set, the slopes of the amplitude spectra for luminance or chromatic contrast were varied independently to create images ranging from strongly blurred to sharpened relative to a “natural” 1/f spectrum. Perceived blur was dominated by the luminance slopes, with discomfort rated lowest for ~1/f spectra. In a second set of focused Mondrians, color was varied along different axes in the LvsM vs. SvsLM chromatic plane. Discomfort ratings were lowest around bluish-yellowish axes that are again typical of natural outdoor scenes. A final set varied in the levels of both luminance and chromatic contrast. Discomfort increased with increasing color contrast or decreasing luminance contrast, and tended toward lower ratings for images with balanced levels of luminance and color contrast. Notably these ratings of discomfort were not related to judgments of artistic merit. Thus for both spatial and chromatic content the least aversive images corresponded to characteristic properties of the natural visual environment, and may reflect a normalization of visual coding to the natural world.

Importance of Visual Acuity and Contrast Sensitivity in Patients With Glaucoma

Abstract: Objective To determine which aspects of vision most influence the ability of patients with glaucoma to function. Methods A total of 192 patients with a full range of glaucomatous visual loss were selected from the Glaucoma Service of Wills Eye Institute. Patients were evaluated clinically with standard visual assessments: visual acuity, contrast sensitivity, visual field, stereopsis, the Disc Damage Likelihood Scale, and intraocular pressure. Patients were evaluated objectively using a comprehensive performance-based measure of visual function, the Assessment of Disability Related to Vision (ADREV), and subjectively with the 25-item National Eye Institute Visual Function Questionnaire. Statistical analyses, including Spearman correlation coefficients and regression analysis, were performed on the data. Results Performance on the ADREV was most strongly associated with binocular visual acuity ( r = −0.79; P r = 0.80; P P Conclusion The aspects of visual function that best predict the ability of a patient with glaucoma to perform activities of daily living are binocular visual acuity and contrast sensitivity.

Phase-contrast X-ray imaging of breast.

Abstract: When an X-ray wave traverses an object, its amplitude and phase change, resulting in attenuation, interference, and refraction, and in phase-contrast X-ray imaging (PCI) these are converted to intensity changes. The relative change of the X-ray phase per unit path length is even orders of magnitude larger than that of the X-ray amplitude, so that the image contrast based on variation of the X-ray phase is potentially much stronger than the contrast based on X-ray amplitude (absorption contrast). An important medical application of PCI methods is soft-tissue imaging, where the absorption contrast is inherently weak. It is shown by in vitro examples that signs of malignant human breast tumor are enhanced in PCI images. Owing to the strong contrast, the radiation dose can be greatly reduced, so that a high-resolution phase-contrast X-ray tomography of the breast is possible with about 1 mGy mean glandular dose. Scattered radiation carries essential information on the atomic and molecular structure of the obj...

Lip colour affects perceived sex typicality and attractiveness of human faces.

Abstract: The luminance contrast between facial features and facial skin is greater in women than in men, and women's use of make-up enhances this contrast. In black-and-white photographs, increased luminance contrast enhances femininity and attractiveness in women's faces, but reduces masculinity and attractiveness in men's faces. In Caucasians, much of the contrast between the lips and facial skin is in redness. Red lips have been considered attractive in women in geographically and temporally diverse cultures, possibly because they mimic vasodilation associated with sexual arousal. Here, we investigate the effects of lip luminance and colour contrast on the attractiveness and sex typicality (masculinity/femininity) of human faces. In a Caucasian sample, we allowed participants to manipulate the colour of the lips in colour-calibrated face photographs along CIELab L* (light--dark), a* (red--green), and b* (yellow--blue) axes to enhance apparent attractiveness and sex typicality. Participants increased redness contrast to enhance femininity and attractiveness of female faces, but reduced redness contrast to enhance masculinity of men's faces. Lip blueness was reduced more in female than male faces. Increased lightness contrast enhanced the attractiveness of both sexes, and had little effect on perceptions of sex typicality. The association between lip colour contrast and attractiveness in women's faces may be attributable to its association with oxygenated blood perfusion indicating oestrogen levels, sexual arousal, and cardiac and respiratory health.

Transcranial direct current stimulation affects visual perception measured by threshold perimetry.

Abstract: In this study, we aimed to characterize the effect of anodal and cathodal direct current stimulation (tDCS) on contrast sensitivity inside the central 10 degrees of the visual field in healthy subjects. Distinct eccentricities were investigated separately, since at the cortical level, more central regions of the visual field are represented closer to the occipital pole, i.e. closer to the polarizing electrodes, than are the more peripheral regions. Using a double-blind and sham-controlled within-subject design, we measured the effect of stimulation and potential learning effect separately across testing days. Anodal stimulation of the visual cortex compared to sham stimulation yielded a significant increase in contrast sensitivity within 8° of the visual field. A significant increase in contrast sensitivity between the conditions “pre” and “post” anodal stimulation was only obtained for the central positions at eccentricities smaller than 2°. Cathodal stimulation of the visual cortex did not affect contrast sensitivity at either eccentricity. Perceptual learning across testing days was only observed for threshold perimetry before stimulation. Measuring contrast sensitivity changes after tDCS with a standard clinical tool such as threshold perimetry may provide an interesting perspective in assessing therapeutic effects of tDCS in ophthalmological or neurological defects (e.g. with foveal sparing vs. foveal splitting).

Linear and Non-linear Contrast Enhancement Image

Abstract: This paper attempts to undertake the study two types of the contrast enhancement techniques, linear contrast techniques and non-linear contrast techniques. In linear contrast techniques applying three methods, Max-Min contrast method, Percentage contrast method and Piecewise contrast technique. Non-linear contrast techniques applying four contrast methods, Histogram equalization method, Adaptive histogram equalization method, Homomorphic Filter method and Unsharpe Mask. in the Homomorphic Filter method applying by using two type of filter, Low Pass Filter(LPF)and High Pass Filter(HPF).this applying to choose the base guesses for contrast enhancement image.

Spatiotemporal laser speckle contrast analysis for blood flow imaging with maximized speckle contrast.

Abstract: Laser speckle contrast imaging is a technique used for imaging blood flow without scanning. Though several studies have attempted to combine spatial and temporal statistics of laser speckle images for reducing image noise as well as preserving acceptable spatiotemporal resolution, the statistical accuracy of these spatiotemporal methods has not been thoroughly compared. Through numerical simulation and animal experiments, this study investigates the changes in the mean speckle contrast values and the relative noise of the speckle contrast images computed by these methods with various numbers of frames and spatial windows. The simulation results show that the maximum relative error of the mean speckle contrast computed by the spatiotemporal laser speckle contrast analysis (STLASCA) method, in which the speckle contrast images are computed by analyzing the 3-D spatiotemporal speckle image cube, is approximately 5%, while it is higher than 13% for other methods. Changes in the mean speckle contrast values and the relative noise computed by these methods for animal experiment data are consistent with the simulation results. Our results demonstrate that STLASCA achieves more accurate speckle contrast, and suggest that STLASCA most effectively utilizes the number of pixels, thus achieving maximized speckle contrast, and thereby maximizing the variation of the laser speckle contrast image.

Customizable graphical display

Abstract: Aspects of the disclosed subject matter are directed to customizing the colors of instruments that are used to convey vehicle readings. In accordance with one embodiment, a method is provided that obtains input to perform a color change to one or more instruments presented on a graphical display. For each instrument affected by the color change, a determination is made regarding whether a threshold level of contrast exists between a symbol graphic of the instrument and one or more background colors. If a threshold level of contrast does not exist, the contrast ratio between the symbol graphic and one or more background colors is adjusted to at least the threshold level. Then the method causes the graphical display to render the one or more instruments in accordance with the received color selections.

Differences in Photoreceptor Processing Speed for Chromatic and Achromatic Vision in the Bumblebee, Bombus terrestris

Abstract: Fast detection of visual change can be mediated by visual processes that ignore chromatic aspects of the visual signal, relying on inputs from a single photoreceptor class (or pooled input from similar classes). There is an established link between photoreceptor processing speed (in achromatic vision) and visual ecology. Highly maneuverable flies, for example, have the fastest know photoreceptors, relying on metabolically expensive membrane conductances to boost performance. Less active species forgo this investment and their photoreceptors are correspondingly slower. However, within a species, additional classes of photoreceptors are required to extract chromatic information, and the question therefore arises as to whether there might be within-species differences in processing speed between photoreceptors involved in chromatic processing compared with those feeding into fast achromatic visual systems. We used intracellular recording to compare light-adapted impulse responses in three spectral classes of photoreceptor in the bumblebee. Green-sensitive photoreceptors, which are known to provide achromatic contrast for motion detection, generated the fastest impulse responses (half-width, Δ t = 7.9 ± 1.1 ms). Blue- and UV-sensitive photoreceptors (which are involved in color vision) were significantly slower (9.8 ± 1.2 and 12.3 ± 1.8 ms, respectively). The faster responses of green photoreceptors are in keeping with their role in fast achromatic vision. However, blue and UV photoreceptors are still relatively fast in comparison with many other insect species, as well as vertebrate cones, suggesting a significant investment in photoreceptor processing for color vision in bees. We discuss this finding in relation to bees' requirement for accurate learning of flower color, especially in conditions of variable luminance contrast.

Contrast and Phase Combination in Binocular Vision

Abstract: Background How the visual system combines information from the two eyes to form a unitary binocular representation of the external world is a fundamental question in vision science that has been the focus of many psychophysical and physiological investigations. Ding & Sperling (2006) measured perceived phase of the cyclopean image, and developed a binocular combination model in which each eye exerts gain control on the other eye's signal and over the other eye's gain control. Critically, the relative phase of the monocular sine-waves plays a central role. Methodology/Principal Findings We used the Ding-Sperling paradigm but measured both the perceived contrast and phase of cyclopean images in three hundred and eighty combinations of base contrast, interocular contrast ratio, eye origin of the probe, and interocular phase difference. We found that the perceived contrast of the cyclopean image was independent of the relative phase of the two monocular gratings, although the perceived phase depended on the relative phase and contrast ratio of the monocular images. We developed a new multi-pathway contrast-gain control model (MCM) that elaborates the Ding-Sperling binocular combination model in two ways: (1) phase and contrast of the cyclopean images are computed in separate pathways, although with shared cross-eye contrast-gain control; and (2) phase-independent local energy from the two monocular images are used in binocular contrast combination. With three free parameters, the model yielded an excellent account of data from all the experimental conditions. Conclusions/Significance Binocular phase combination depends on the relative phase and contrast ratio of the monocular images but binocular contrast combination is phase-invariant. Our findings suggest the involvement of at least two separate pathways in binocular combination.

The what and why of perceptual asymmetries in the visual domain.

Abstract: Perceptual asymmetry is one of the most important characteristics of our visual functioning. We carefully reviewed the scientific literature in order to examine such asymmetries, separating them into two major categories: within-visual field asymmetries and between-visual field asymmetries. We explain these asymmetries in terms of perceptual aspects or tasks, the what of the asymmetries; and in terms of underlying mechanisms, the why of the asymmetries. Tthe within-visual field asymmetries are fundamental to orientation, motion direction, and spatial frequency processing. between-visual field asymmetries have been reported for a wide range of perceptual phenomena. foveal dominance over the periphery, in particular, has been prominent for visual acuity, contrast sensitivity, and colour discrimination. Tthis also holds true for object or face recognition and reading performance. upper-lower visual field asymmetries in favour of the lower have been demonstrated for temporal and contrast sensitivities, visual acuity, spatial resolution, orientation, hue and motion processing. Iin contrast, the upper field advantages have been seen in visual search, apparent size, and object recognition tasks. left-right visual field asymmetries include the left field dominance in spatial (e.g., orientation) processing and the right field dominance in non-spatial (e.g., temporal) processing. left field is also better at low spatial frequency or global and coordinate spatial processing, whereas the right field is better at high spatial frequency or local and categorical spatial processing. All these asymmetries have inborn neural/physiological origins, the primary why, but can be also susceptible to visual experience, the critical why (promotes or blocks the asymmetries by altering neural functions).

Spatial Contrast Sensitivity in Adolescents with Autism Spectrum Disorders

Abstract: Adolescents with autism spectrum disorders (ASD) and typically developing (TD) controls underwent a rigorous psychophysical assessment that measured contrast sensitivity to seven spatial frequencies (0.5-20 cycles/degree). A contrast sensitivity function (CSF) was then fitted for each participant, from which four measures were obtained: visual acuity, peak spatial frequency, peak contrast sensitivity, and contrast sensitivity at a low spatial frequency. There were no group differences on any of the four CSF measures, indicating no differential spatial frequency processing in ASD. Although it has been suggested that detail-oriented visual perception in individuals with ASD may be a result of differential sensitivities to low versus high spatial frequencies, the current study finds no evidence to support this hypothesis.

Bayesian Model of Dynamic Image Stabilization in the Visual System

Abstract: Humans can resolve the fine details of visual stimuli although the image projected on the retina is constantly drifting relative to the photoreceptor array. Here we demonstrate that the brain must take this drift into account when performing high acuity visual tasks. Further, we propose a decoding strategy for interpreting the spikes emitted by the retina, which takes into account the ambiguity caused by retinal noise and the unknown trajectory of the projected image on the retina. A main difficulty, addressed in our proposal, is the exponentially large number of possible stimuli, which renders the ideal Bayesian solution to the problem computationally intractable. In contrast, the strategy that we propose suggests a realistic implementation in the visual cortex. The implementation involves two populations of cells, one that tracks the position of the image and another that represents a stabilized estimate of the image itself. Spikes from the retina are dynamically routed to the two populations and are interpreted in a probabilistic manner. We consider the architecture of neural circuitry that could implement this strategy and its performance under measured statistics of human fixational eye motion. A salient prediction is that in high acuity tasks, fixed features within the visual scene are beneficial because they provide information about the drifting position of the image. Therefore, complete elimination of peripheral features in the visual scene should degrade performance on high acuity tasks involving very small stimuli.

The relationship between visual function, duration and main causes of vision loss and falls in older people with low vision.

Abstract: Falls are an alarming health problem and a major cause of injury among the elderly. The healthcare cost associated with falls is considerable. Visual acuity has been found to be an independent risk factor for falls; however, the results are not unanimous. Moreover, other aspects of visual function such as visual field, contrast sensitivity and depth perception have not been adequately investigated in relation to falls. The aim of this study, therefore, was to determine the relationship between visual function, duration, and main causes of visual impairment, and falls in individuals with low vision. This was a cross-sectional study involving participants attending a public tertiary eye care hospital. Participants were mobile, aged 60 years or above, and had low vision (visual acuity >0.3 LogMAR in the better eye). Details about falls in the previous 12 months and other information were collected, and patients completed a questionnaire about activities of daily living. The duration and main causes of visual impairment, visual acuity, contrast sensitivity, depth perception, and visual field were assessed. Descriptive statistical analyses were performed to characterize the participants’ sociodemographic and clinical data. One hundred and twenty seven patients (53%; 67 males) with a mean age of 76.3 ± 8.3 years were recruited. Thirty seven percent of the participants (n = 47) had mild, 50% (n = 64) moderate and 13% (n = 16) severe visual impairment (>0.3–0.5; >0.5–1.0; and >1.0 LogMAR respectively). The frequencies of single and multiple falls were 42.5% and 12.6% respectively. Visual acuity, contrast sensitivity, depth perception, visual field, main cause, and duration of visual impairment were not significantly associated with falls (p > 0.05). In multiple regression analyses, physical inactivity remained the only variable independently associated with falls in all models except for visual field. Overall, visually impaired people were three times more likely to fall if they were physically inactive. Visual function, duration and main causes of visual impairment are not independently associated with falls in people with low vision. However, a significant relationship between non-participation in physical activity and falls was found. Further work is required to investigate the association between vision-related factors and falls in older people with visual impairment.

When doors of perception open: visual contrast sensitivity in never-medicated, first-episode schizophrenia.

Abstract: Schizophrenia is characterized by impaired visual contrast sensitivity and anomalous perceptual experiences. The aim of this study was to investigate these phenomena in unmedicated patients with first-episode schizophrenia. Visual contrast sensitivity was measured with pulsed-pedestal and steady-pedestal tests, which bias information processing toward the parvocellular and magnocellular pathways, respectively. Anomalous perceptual experiences were investigated with the Structured Interview for Assessing Perceptual Anomalies (SIAPA). Results revealed that patients with schizophrenia (n = 20) exhibited increased contrast sensitivity values on the magnocellular test relative to the control participants (n = 20). In the parvocellular condition, there was no significant difference between the two groups. The higher magnocellular contrast sensitivity values were associated with increased visual SIAPA scores, especially at the two lowest spatial frequencies (0.25 and 0.5 cycles/degree). These results indicate the heightened sensitivity of magnocellular pathways in unmedicated first-episode schizophrenia, which may contribute to anomalous perceptual experiences and sensory overloading.

Effects of retinal morphology on contrast sensitivity and reading ability in neovascular age-related macular degeneration.

Abstract: In recent years, the treatment of neovascular age-related macular degeneration (AMD) has been revolutionized by the introduction of antiangiogenic therapies such as ranibizumab (Lucentis), and bevacizumab (Avastin; both from Genentech, Inc., South San Francisco, CA).1–3 Optical coherence tomography (OCT), an imaging modality that provides cross-sectional images of the neurosensory retina, plays a critical role in this treatment by allowing noninvasive monitoring of disease activity.4,5 Although it is presumed that anatomic improvements demonstrated by OCT will ultimately result in clinical benefits, many studies have failed to show a consistent correlation between reduction in OCT-derived retinal thickness and improvement in visual function.3,6 Such failures may be due, at least in part, to the limitations of the automated image-analysis software provided by current OCT systems.7,8 In addition, however, the structurally heterogeneous nature of the disorder and the reliance on high-contrast distance visual acuity as the primary measure of visual function in these studies may play a role.9,10 CNV, the hallmark of neovascular AMD, results in a wide range of alterations in retinal morphology, with intraretinal, subretinal, and RPE components.11,12 CNV lesions also vary widely, both in size, and in location relative to the fovea. Although high-contrast distance visual acuity is largely a function of foveal integrity, other visual parameters, such as reading ability and contrast sensitivity, may be more reflective of alterations in macular structure as a whole.10,13–15 Thus, evaluation of contrast sensitivity and reading ability may allow detection of stronger and more consistent correlations with OCT-derived retinal parameters. The detection of any such robust relationship is of interest for clinical trials, where the use of validated morphologic parameters as surrogate endpoints could lead to increased accuracy, reduced costs, and shortened duration.16–18 Furthermore, in clinical practice, measurement of reading ability and contrast sensitivity may also allow the clinician to better assess individual visual performance. Contrast sensitivity, for example, is closely linked with both orientation and mobility and, in patients with macular disease, may be markedly reduced despite near-normal distance visual acuity.19 To address these questions and others, we have developed a software tool (OCTOR) that allows the user to manually quantify any retinal structure of interest.20 Using this tool, we have identified novel OCT parameters that show modest correlations with Snellen visual acuity in neovascular AMD.6,9 In the current report, we evaluate the effect of changes in retinal morphology on reading ability and contrast sensitivity, using OCTOR, in a recently completed phase III/IV clinical trial: the Avastin (bevacizumab) for choroidal neovascularization (ABC) Trial.21

Spatial standard observer

Abstract: The present invention relates to devices and methods for the measurement and/or for the specification of the perceptual intensity of a visual image, or the perceptual distance between a pair of images. Grayscale test and reference images are processed to produce test and reference luminance images. A luminance filter function is convolved with the reference luminance image to produce a local mean luminance reference image. Test and reference contrast images are produced from the local mean luminance reference image and the test and reference luminance images respectively, followed by application of a contrast sensitivity filter. The resulting images are combined according to mathematical prescriptions to produce a Just Noticeable Difference, JND value, indicative of a Spatial Standard Observer, SSO. Some embodiments include masking functions, window functions, special treatment for images lying on or near borders and pre-processing of test images.

A Space-Variant Luminance Map based Color Image Enhancement

Abstract: Improvement of image quality has been highly demanding for users in digital imaging systems. A variety of image enhancement algorithms has been developed to control image enhancement factors. This paper presents a color image enhancement method that makes use of a space-variant luminance map (SVLM) for the local brightness characterization. Two-dimensional gamma correction combined with the SVLM is developed to increase the intensity at the dark region and vice versa at the bright region in the luminance domain. The enhanced luminance information is applied to the adaptive contrast enhancing process and the linear color restoration. The proposed algorithm reveals details of the input image as well as minimizes loss of the edge sharpness in the non-uniform and low illumination conditions. The developed enhancement process resulted in the lowest absolute mean brightness error (AMBE) in a low-complexity fashion. A series of experimental results are discussed in terms of visual quality, the enhancement performance, and the complexity.

A Five-Decade Dynamic-Range Ambient-Light-Independent Calibrated Signed-Spatial-Contrast AER Retina With 0.1-ms Latency and Optional Time-to-First-Spike Mode

Abstract: Address Event Representation (AER) is an emergent technology for assembling modular multiblock bio-inspired sensory and processing systems. Visual sensors (retinae) are among the first AER modules to be reported since the introduction of the technology. Spatial-contrast AER retinae are of special interest since they provide highly compressed data flow without reducing the relevant information required for performing recognition. The reported AER contrast retinae perform a contrast computation based on the ratio between a pixel's local light intensity and a spatially weighted average of its neighborhood. This resulted in compact circuits but with the penalty of all pixels generating output signals even if they sensed no contrast. In this paper, we present a spatial-contrast retina with a signed output: Contrast is computed as the relative difference (not the ratio) between a pixel's local light and its surrounding spatial average and normalized with respect to ambient light. As a result, contrast is ambient light independent, includes a sign, and the output will be zero if there is no contrast. Furthermore, an adjustable thresholding mechanism has been included, such that pixels remain silent until they sense an absolute contrast above the adjustable threshold. The pixel contrast-computation circuit is based on Boahen's biharmonic operator contrast circuit, which has been improved to include mismatch calibration and adaptive-current-based biasing. As a result, the contrast-computation circuit shows much less mismatch, is almost insensitive to ambient light illumination, and biasing is much less critical than in the original voltage biasing scheme. The retina includes an optional global reset mechanism for operation in ambient-light-independent Time-to-First-Spike contrast-computation mode. A 32 32 pixel test prototype has been fabricated in 0.35-m CMOS. Experimental results are provided.

Contrast gain control and cortical TrkB signaling shape visual acuity

Abstract: In addition to the neurotropic role of brain-derived neurotrophic factor (BNDF) in cortical circuit plasticity, there is a good positive correlation between the cortical expression level of BDNF and developmental changes in visual acuity. Here, the authors find that directly impairing BDNF signaling using transgenic methods causes visual impairment by affecting the systems level control on contrast gain. During development and aging and in amblyopia, visual acuity is far below the limitations set by the retina. Expression of brain-derived neurotrophic factor (BDNF) in the visual cortex is reduced in these situations. We asked whether neurotrophic tyrosine kinase receptor, type 2 (TrkB) regulates cortical visual acuity in adult mice. We found that genetically interfering with TrkB/BDNF signaling in pyramidal cells in the mature visual cortex reduced synaptic strength and resulted in a loss of neural responses to high spatial-frequency stimuli. Responses to low spatial-frequency stimuli were unaffected. This selective loss was not accompanied by a change in receptive field sizes or plasticity, but apparent contrast was reduced. Our results indicate that a dependence on spatial frequency in the Heeger normalization model explains this selective effect of contrast reduction on high-resolution vision and suggest that it involves contrast gain control operating in the visual cortex.