Wideband enhancement of television images for people with visual impairments

The Effect of Zoom Magnification and Large Display on Video Comprehension in Individuals With Central Vision Loss

Purpose

A larger display at the same viewing distance provides relative-size magnification for individuals with central vision loss (CVL). However, the resulting large visible area of the display is expected to result in more head rotation, which may cause discomfort. We created a zoom magnification technique that placed the center of interest (COI) in the center of the display to reduce the need for head rotation.

Methods

In a 2 × 2 within-subject study design, 23 participants with CVL viewed video clips from 1.5 m (4.9 feet) shown with or without zoom magnification, and with a large (208 cm/82" diagonal, 69°) or a typical (84 cm/33", 31°) screen. Head position was tracked and a custom questionnaire was used to measure discomfort.

Results

Video comprehension was better with the large screen (P < 0.001) and slightly worse with zoom magnification (P = 0.03). Oddly, head movements did not vary with screen size (P = 0.63), yet were greater with zoom magnification (P = 0.001). This finding was unexpected, because the COI remains in the center with zoom magnification, but moves widely with a large screen and no magnification.

Conclusions

This initial attempt to implement the zoom magnification method had flaws that may have decreased its effectiveness. In the future, we propose alternative implementations for zoom magnification, such as variable magnification.

Translational Relevance

We present the first explicit demonstration that relative-size magnification improves the video comprehension of people with CVL when viewing video.

An implementation of Bubble Magnification did not improve the video comprehension of individuals with central vision loss

PURPOSE

People with central vision loss (CVL) watch television, videos and movies, but often report difficulty and have reduced video comprehension. An approach to assist viewing videos is electronic magnification of the video itself, such as Bubble Magnification.

METHODS

We created a Bubble Magnification technique that displayed a magnified segment around the centre of interest (COI) as determined by the gaze of participants with normal vision. The 15 participants with CVL viewed video clips shown with 2× and 3× Bubble Magnification, and unedited. We measured video comprehension and gaze coherence.

RESULTS

Video comprehension was significantly worse with both 2× (p = 0.01) and 3× Bubble Magnification (p < 0.001) than the unedited video. There was no difference in gaze coherence across conditions (p ≥ 0.58). This was unexpected because we expected a benefit in both video comprehension and gaze coherence. This initial attempt to implement the Bubble Magnification method had flaws that probably reduced its effectiveness.

CONCLUSIONS

In the future, we propose alternative implementations of Bubble Magnification, such as variable magnification and bubble size. This study is a first step in the development of an intelligent-magnification approach to providing a vision rehabilitation aid to assist people with CVL.

Applications of augmented reality in ophthalmology [Invited]

Throughout the last decade, augmented reality (AR) head-mounted displays (HMDs) have gradually become a substantial part of modern life, with increasing applications ranging from gaming and driver assistance to medical training. Owing to the tremendous progress in miniaturized displays, cameras, and sensors, HMDs are now used for the diagnosis, treatment, and follow-up of several eye diseases. In this review, we discuss the current state-of-the-art as well as potential uses of AR in ophthalmology. This review includes the following topics: (i) underlying optical technologies, displays and trackers, holography, and adaptive optics; (ii) accommodation, 3D vision, and related problems such as presbyopia, amblyopia, strabismus, and refractive errors; (iii) AR technologies in lens and corneal disorders, in particular cataract and keratoconus; (iv) AR technologies in retinal disorders including age-related macular degeneration (AMD), glaucoma, color blindness, and vision simulators developed for other types of low-vision patients.

The Impact of Field of View on Understanding of a Movie Is Reduced by Magnifying Around the Center of Interest

Purpose

Magnification is commonly used to reduce the impact of impaired central vision. However, magnification limits the field of view (FoV) which may make it difficult to follow the story. Most people with normal vision look in about the same place at about the same time, the center of interest (COI), when watching “Hollywood” movies. We hypothesized that if the FoV was centered at the COI, then this view would provide more useful information than either the original image center or an unrelated view location (the COI locations from a different video clip) as the FoV reduced.

Methods

The FoV was varied between 100% (original) and 3%. To measure video comprehension as the FoV reduced, subjects described 30-second video clips in response to two open-ended questions. A computational, natural-language approach was used to provide an information acquisition (IA) score.

Results

The IA scores reduced as the FoV decreased. When the FoV was around the COI, subjects were better able to understand the content of the video clips (higher IA scores) as the FoV decreased than the other conditions. Thus, magnification around the COI may serve as a better video enhancement approach than simple magnification of the image center.

Conclusions

These results have implications for future image processing and scene viewing, which may help people with central vision loss view directed dynamic visual content (“Hollywood” movies).

Translational Relevance

Our results are promising for the use of magnification around the COI as a vision rehabilitation aid for people with central vision loss.

Comparing object recognition from binary and bipolar edge images for visual prostheses

Visual prostheses require an effective representation method due to the limited display condition which has only 2 or 3 levels of grayscale in low resolution. Edges derived from abrupt luminance changes in images carry essential information for object recognition. Typical binary (black and white) edge images have been used to represent features to convey essential information. However, in scenes with a complex cluttered background, the recognition rate of the binary edge images by human observers is limited and additional information is required. The polarity of edges and cusps (black or white features on a gray background) carries important additional information; the polarity may provide shape from shading information missing in the binary edge image. This depth information may be restored by using bipolar edges. We compared object recognition rates from 16 binary edge images and bipolar edge images by 26 subjects to determine the possible impact of bipolar filtering in visual prostheses with 3 or more levels of grayscale. Recognition rates were higher with bipolar edge images and the improvement was significant in scenes with complex backgrounds. The results also suggest that erroneous shape from shading interpretation of bipolar edges resulting from pigment rather than boundaries of shape may confound the recognition.

Comparing object recognition from binary and bipolar edge features

Edges derived from abrupt luminance changes in images carry essential information for object recognition. Typical binary edge images (black edges on white background or white edges on black background) have been used to represent features (edges and cusps) in scenes. However, the polarity of cusps and edges may contain important depth information (depth from shading) which is lost in the binary edge representation. This depth information may be restored, to some degree, using bipolar edges. We compared recognition rates of 16 binary edge images, or bipolar features, by 26 subjects. Object recognition rates were higher with bipolar edges and the improvement was significant in scenes with complex backgrounds.

High Tech Aids Low Vision: A Review of Image Processing for the Visually Impaired

Recent advances in digital image processing provide promising methods for maximizing the residual vision of the visually impaired. This paper seeks to introduce this field to the readership and describe its current state as found in the literature. A systematic search revealed 37 studies that measure the value of image processing techniques for subjects with low vision. The techniques used are categorized according to their effect and the principal findings are summarized. The majority of participants preferred enhanced images over the original for a wide range of enhancement types. Adapting the contrast and spatial frequency content often improved performance at object recognition and reading speed, as did techniques that attenuate the image background and a technique that induced jitter. A lack of consistency in preference and performance measures was found, as well as a lack of independent studies. Nevertheless, the promising results should encourage further research in order to allow their widespread use in low-vision aids.

An augmented-reality edge enhancement application for Google Glass

PURPOSE

Google Glass provides a platform that can be easily extended to include a vision enhancement tool. We have implemented an augmented vision system on Glass, which overlays enhanced edge information over the wearer's real-world view, to provide contrast-improved central vision to the Glass wearers. The enhanced central vision can be naturally integrated with scanning.

METHODS

Google Glass' camera lens distortions were corrected by using an image warping. Because the camera and virtual display are horizontally separated by 16 mm, and the camera aiming and virtual display projection angle are off by 10°, the warped camera image had to go through a series of three-dimensional transformations to minimize parallax errors before the final projection to the Glass' see-through virtual display. All image processes were implemented to achieve near real-time performance. The impacts of the contrast enhancements were measured for three normal-vision subjects, with and without a diffuser film to simulate vision loss.

RESULTS

For all three subjects, significantly improved contrast sensitivity was achieved when the subjects used the edge enhancements with a diffuser film. The performance boost is limited by the Glass camera's performance. The authors assume that this accounts for why performance improvements were observed only with the diffuser filter condition (simulating low vision).

CONCLUSIONS

Improvements were measured with simulated visual impairments. With the benefit of see-through augmented reality edge enhancement, natural visual scanning process is possible and suggests that the device may provide better visual function in a cosmetically and ergonomically attractive format for patients with macular degeneration.

Hierarchy of nonlocal means for preferred automatic sharpness enhancement and tone mapping

Existing hierarchical techniques that decompose an image into a smooth image and high frequency components based on Gaussian filter and bilateral filter suffer from halo effects, whereas techniques based on weighted least squares extract low contrast features as details. Other techniques require multiple images and are not tolerant to noise. We use a single image to enhance sharpness based on a hierarchical framework using a modified Laplacian pyramid. In order to ensure robustness, we remove noise by using an extra level in the hierarchical framework. We use an edge-preserving nonlocal means filter and modify it to remove potential halo effects and gradient reversals. However, these effects are only reduced but not removed completely after similar modifications are made to the bilateral filter. We compare our results with existing techniques and show better decomposition and enhancement. Based on validation by human observers, we introduce a new measure to quantify sharpness quality, which allows us to automatically set parameters in order to achieve preferred sharpness enhancement. This causes blurry images to be sharpened more and sufficiently sharp images not to be sharpened. Finally, we demonstrate applications in the context of robust high dynamic range tone mapping that is better than state-of-the-art approaches and enhancement of archaeological artifacts.

Visual search with image modification in age-related macular degeneration

PURPOSE

AMD results in loss of central vision and a dependence on low-resolution peripheral vision. While many image enhancement techniques have been proposed, there is a lack of quantitative comparison of the effectiveness of enhancement. We developed a natural visual search task that uses patients' eye movements as a quantitative and functional measure of the efficacy of image modification.

METHODS

Eye movements of 17 patients (mean age = 77 years) with AMD were recorded while they searched for target objects in natural images. Eight different image modification methods were implemented and included manipulations of local image or edge contrast, color, and crowding. In a subsequent task, patients ranked their preference of the image modifications.

RESULTS

Within individual participants, there was no significant difference in search duration or accuracy across eight different image manipulations. When data were collapsed across all image modifications, a multivariate model identified six significant predictors for normalized search duration including scotoma size and acuity, as well as interactions among scotoma size, age, acuity, and contrast (P < 0.05). Additionally, an analysis of image statistics showed no correlation with search performance across all image modifications. Rank ordering of enhancement methods based on participants' preference revealed a trend that participants preferred the least modified images (P < 0.05).

CONCLUSIONS

There was no quantitative effect of image modification on search performance. A better understanding of low- and high-level components of visual search in natural scenes is necessary to improve future attempts at image enhancement for low vision patients. Different search tasks may require alternative image modifications to improve patient functioning and performance.

Effects of contour enhancement on low-vision preference and visual search

PURPOSE

To determine whether image enhancement improves visual search performance and whether enhanced images were also preferred by subjects with vision impairment.

METHODS

Subjects (n = 24) with vision impairment (vision: 20/52 to 20/240) completed visual search and preference tasks for 150 static images that were enhanced to increase object contours' visual saliency. Subjects were divided into two groups and were shown three enhancement levels. Original and medium enhancements were shown to both groups. High enhancement was shown to group 1, and low enhancement was shown to group 2. For search, subjects pointed to an object that matched a search target displayed at the top left of the screen. An "integrated search performance" measure (area under the curve of cumulative correct response rate over search time) quantified performance. For preference, subjects indicated the preferred side when viewing the same image with different enhancement levels on side-by-side high-definition televisions.

RESULTS

Contour enhancement did not improve performance in the visual search task. Group 1 subjects significantly (p < 0.001) rejected the High enhancement, and showed no preference for medium enhancement over the original images. Group 2 subjects significantly preferred (p < 0.001) both the medium and the low enhancement levels over original. Contrast sensitivity was correlated with both preference and performance; subjects with worse contrast sensitivity performed worse in the search task (ρ = 0.77, p < 0.001) and preferred more enhancement (ρ = -0.47, p = 0.02). No correlation between visual search performance and enhancement preference was found. However, a small group of subjects (n = 6) in a narrow range of mid-contrast sensitivity performed better with the enhancement, and most (n = 5) also preferred the enhancement.

CONCLUSIONS

Preferences for image enhancement can be dissociated from search performance in people with vision impairment. Further investigations are needed to study the relationships between preference and performance for a narrow range of mid-contrast sensitivity where a beneficial effect of enhancement may exist.

Development and evaluation of vision rehabilitation devices

We have developed a range of vision rehabilitation devices and techniques for people with impaired vision due to either central vision loss or severely restricted peripheral visual field. We have conducted evaluation studies with patients to test the utilities of these techniques in an effort to document their advantages as well as their limitations. Here we describe our work on a visual field expander based on a head mounted display (HMD) for tunnel vision, a vision enhancement device for central vision loss, and a frequency domain JPEG/MPEG based image enhancement technique. All the evaluation studies included visual search paradigms that are suitable for conducting indoor controllable experiments.

Dynamic image pre-compensation for computer access by individuals with ocular aberrations

Several image enhancement methods have been successfully used to improve the visual perception of patients with eye diseases, such as Age-related Macular Degeneration and Cataracts, on images displayed on TV and computers. However, few developments aim to enhance the visual performance of computer users with general ocular aberrations. This paper proposes an image enhancement approach based on dynamic pre-compensation for improving the visual performance of subjects with ocular aberrations, while interacting with computers. The degradation caused by ocular aberrations is counteracted through the pre-compensation performed on images displayed on the computer screen. As the ocular aberration initially measured as a priori information is related with a specific pupil size, real-time pupil size data are collected to recalculate and update the pre-compensation to match the corresponding aberrations. An icon recognition experiment, involving human subjects, was designed and implemented to evaluate the performance of the proposed method. The experimental results show that the proposed method significantly increased the number of icons correctly recognized, which confirmed that the dynamic pre-compensation is effective in improving the visual performance of computer users with ocular aberrations.

IMAGE ENHANCEMENT FOR IMPAIRED VISION: THE CHALLENGE OF EVALUATION

With the aging of the population, the prevalence of eye diseases and thus of vision impairment is increasing. The TV watching habits of people with vision impairments are comparable to normally sighted people1, however their vision loss prevents them from fully benefiting from this medium. For over 20 years we have been developing video image-enhancement techniques designed to assist people with visual impairments, particularly those due to central retinal vision loss. A major difficulty in this endeavor is the lack of evaluation techniques to assess and compare the effectiveness of various enhancement methods. This paper reviews our approaches to image enhancement and the results we have obtained, with special emphasis on the difficulties encountered in the evaluation of the benefits of enhancement and the solutions we have developed to date.

DEVELOPMENT AND EVALUATION OF VISION MULTIPLEXING DEVICES FOR VISION IMPAIRMENTS

We have proposed a novel concept of vision multiplexing for the visually impaired - superimposing contour images over their natural view of a scene or over original images presented on a TV screen. We have implemented the concept using an optical see-through head mounted display to provide either visual field expansion to patients with peripheral field loss or vision enhancement to patients with central vision loss. We have also implemented the concept in a video player with dynamic magnification for patients with central vision loss. Results of initial testing in the lab and on the street are promising.

Influence of background on image recognition in normal vision and age-related macular degeneration

PURPOSE

The influence of background attenuation on the spatial frequency bandwidth requirements for image recognition was assessed in normal young and older groups and in a group with age-related macular degeneration (AMD). Bandwidth requirements were also assessed in the visual periphery of young normal observers.

METHODS

In Experiment 1, each observer was presented with 20 series of images. Each series consisted of a sequence of progressively low-pass filtered images, presented in an order of increasing bandwidth, i.e., according to an ascending method of limits. For half of the series, the background of the base image was selectively darkened by 80% of its original luminance. Three measures were analyzed: (1) the critical bandwidth defined as the bandwidth in cycles/image (cpi) at which 50% of the images were recognized, (2) the minimal bandwidth, defined as the minimal bandwidth at which images were recognized and (3) the proportion of images recognized at full bandwidth. In Experiment 2, young normal observers were similarly tested in central vision and at 5.5° eccentricity (superior or inferior visual field). A third background attenuation condition was included, as well, in which the background was low-pass filtered.

RESULTS

The critical bandwidth for image recognition was significantly reduced by darkening the image background for normal young and old and the AMD groups. This improvement was found to be contrast dependent for the darkened background. In addition, AMD observers tended to recognize more images at full bandwidth if the background was darkened. For normal young observers, making the background low-pass was ineffective in lowering the critical bandwidth in the fovea. Fewer images were recognized at full bandwidth at 5.5° eccentricity for a low-pass background and marginally fewer for a darkened background.

CONCLUSIONS

Selective attenuation of the image background can lead to reductions in the bandwidth requirements for image recognition in AMD. However, performance of young normal observers for images presented in the periphery was unlike AMD performance under the conditions investigated. These results have interesting implications for the design of image enhancement algorithms to aid low vision observers.

Television, computer and portable display device use by people with central vision impairment

PURPOSE

To survey the viewing experience (e.g. hours watched, difficulty) and viewing metrics (e.g. distance viewed, display size) for television (TV), computers and portable visual display devices for normally-sighted (NS) and visually impaired participants. This information may guide visual rehabilitation.

METHODS

Survey was administered either in person or in a telephone interview on 223 participants of whom 104 had low vision (LV, worse than 6/18, age 22-90 years, 54 males), and 94 were NS (visual acuity 6/9 or better, age 20-86 years, 50 males). Depending on their situation, NS participants answered up to 38 questions and LV participants answered up to a further 10 questions.

RESULTS

Many LV participants reported at least 'some' difficulty watching TV (71/103), reported at least 'often' having difficulty with computer displays (40/76) and extreme difficulty watching videos on handheld devices (11/16). The average daily TV viewing was slightly, but not significantly, higher for the LV participants (3.6 h) than the NS (3.0 h). Only 18% of LV participants used visual aids (all optical) to watch TV. Most LV participants obtained effective magnification from a reduced viewing distance for both TV and computer display. Younger LV participants also used a larger display when compared to older LV participants to obtain increased magnification. About half of the TV viewing time occurred in the absence of a companion for both the LV and the NS participants. The mean number of TVs at home reported by LV participants (2.2) was slightly but not significantly (p = 0.09) higher than NS participants (2.0). LV participants were equally likely to have a computer but were significantly (p = 0.004) less likely to access the internet (73/104) compared to NS participants (82/94). Most LV participants expressed an interest in image enhancing technology for TV viewing (67/104) and for computer use (50/74), if they used a computer.

CONCLUSIONS

In this study, both NS and LV participants had comparable video viewing habits. Most LV participants in our sample reported difficulty watching TV, and indicated an interest in assistive technology, such as image enhancement. As our participants reported that at least half their video viewing hours are spent alone and that there is usually more than one TV per household, this suggests that there are opportunities to use image enhancement on the TVs of LV viewers without interfering with the viewing experience of NS viewers.

Designing and testing scene enhancement algorithms for patients with retina degenerative disorders

Background

Retina degenerative disorders represent the primary cause of blindness in UK and in the developed world. In particular, Age Related Macular Degeneration (AMD) and Retina Pigmentosa (RP) diseases are of interest to this study. We have therefore created new image processing algorithms for enhancing the visual scenes for them.

Methods

In this paper we present three novel image enhancement techniques aimed at enhancing the remaining visual information for patients suffering from retina dystrophies. Currently, the only effective way to test novel technology for visual enhancement is to undergo testing on large numbers of patients. To test our techniques, we have therefore built a retinal image processing model and compared the results to data from patient testing. In particular we focus on the ability of our image processing techniques to achieve improved face detection and enhanced edge perception.

Results

Results from our model are compared to actual data obtained from testing the performance of these algorithms on 27 patients with an average visual acuity of 0.63 and an average contrast sensitivity of 1.22. Results show that Tinted Reduced Outlined Nature (TRON) and Edge Overlaying algorithms are most beneficial for dynamic scenes such as motion detection. Image Cartoonization was most beneficial for spatial feature detection such as face detection. Patient's stated that they would most like to see Cartoonized images for use in daily life.

Conclusions

Results obtained from our retinal model and from patients show that there is potential for these image processing techniques to improve visual function amongst the visually impaired community. In addition our methodology using face detection and efficiency of perceived edges in determining potential benefit derived from different image enhancement algorithms could also prove to be useful in quantitatively assessing algorithms in future studies.

A versatile optoelectronic aid for low vision patients

The purpose of this work is to describe a versatile optoelectronic aid for low vision rehabilitation based on reconfigurable hardware. This aid is easily adaptable to diverse pathologies (with different associated processing tasks) and to the progression of the visual impairment. This platform has a mobile configuration that uses a see-through head-mounted display (Nomad). We have implemented different types of vision enhancement on this versatile platform, and briefly summarize here their computational costs (in terms of hardware resource requirements). We have evaluated two representative capabilities of this aid (Augmented View and digital zoom) with measurements of visual acuity, contrast sensitivity and visual field. We have tested the Nomad head-mounted display and the Augmented View modality, in eight subjects with retinitis pigmentosa: the digital zoom was tested in six low vision subjects and nine normally-sighted subjects. We show that the Nomad display with Augmented View configuration does not impair the residual vision; and that there is an increase in visual acuity (VA) with the digital zoom configuration. The major advantage of this platform is that it can easily embed different image processing tasks and since it is based on a FPGA device, it can be specifically configured to tasks requiring real-time processing.

Custom-devised and generic digital enhancement of images for people with maculopathy

AIM

The purpose of this study was to compare the effectivity, in terms of the potential usefulness, of digital filters based on either contrast sensitivity (CS) or supra-threshold contrast matching (CM) in enhancing pictures images for people with maculopathy and to investigate whether generic filters (not based on an individual's vision loss) are equally as effective. Effectivity is measured by changes in perceived visibility.

METHODS

Thirty-five subjects with maculopathy, aged 20-92 years, took part [13 atrophic age-related macular degeneration (ARMD), 14 exudative ARMD, and 8 juvenile macular dystrophy (JMD)]. CS and supra-threshold CM were measured. A range of CS filters (1 or 2-octave wide band-pass filter using a Gabor or polynomial envelope) with different strengths were developed based on the ratio of the individual's contrast threshold and that of a normal age-related group. Similarly filters were developed based on CM at 3.6% and 27.9% contrast. The following generic filters were also applied with different 'strengths': edge enhancement; sharpening; contrast enhancement; Peli's adaptive enhancement; difference of Gaussian; and an equi-emphasis band-pass filter. The filters were applied to images of faces and general scenes. Subjects were asked to rank the perceived visibility of images (to obtain the best version of each filter) and then to rate the perceived visibility of each image filtered with a particular filter.

RESULTS

In general, subjects with atrophic ARMD and JMD preferred the weaker versions of most of the filters, while those with exudative ARMD did not show such a clear preference. Generally, images of faces were preferred with less enhancement than scenes. The filters based on CM were rated as giving significant improvement, while those based on CS and peak emphasis were not preferred. Of the generic filters, the Peli adaptive enhancement filter was most frequently rated as giving a significant improvement (p < 0.05) followed by the contrast enhancement filter. They gave the same perceived enhancement as the custom-devised filters.

CONCLUSIONS

Generic filters, which are easier to apply than the custom-devised filters, are appropriate for rehabilitation purposes.

Inattentional blindness and augmented-vision displays: effects of cartoon-like filtering and attended scene

Augmented-vision devices that we are developing to aid people with low vision (impaired vision) employ vision multiplexing- the simultaneous presentation of two different views to one or both eyes. This approach enables compensation for vision deficits without depriving the wearers of their normal views of the scene. Ideally, wearers would make use of the simultaneous views to alert them to potential mobility hazards, without a need to divide attention consciously. Inattentional blindness, the frequent inability to notice otherwise-obvious events in one scene while paying attention to another, overlapping, scene, works against that sort of augmentation, so we are investigating ways to mitigate it. In this study, we filtered the augmented view, creating cartoon-like representations, to make it easier to detect significant features in that view and to minimise interference with the normal view. We reproduced a classic inattentional blindness experiment to evaluate the effect, and found that, surprisingly, edge filtering had no detectable effect - positive or negative - on the noticing of unexpected events in the unattended scene. We then modified the experiment to determine if the inattentional blindness was because of the confusion of overlaid views or simply a matter of attention, and found the latter to be the case.

Applications of Augmented Vision Head-Mounted Systems in Vision Rehabilitation

Vision loss typically affects either the wide peripheral vision (important for mobility), or central vision (important for seeing details). Traditional optical visual aids usually recover the lost visual function, but at a high cost for the remaining visual function. We have developed a novel concept of vision-multiplexing using augmented vision head-mounted display systems to address vision loss. Two applications are discussed in this paper. In the first, minified edge images from a head-mounted video camera are presented on a see-through display providing visual field expansion for people with peripheral vision loss, while still enabling the full resolution of the residual central vision to be maintained. The concept has been applied in daytime and nighttime devices. A series of studies suggested that the system could help with visual search, obstacle avoidance, and nighttime mobility. Subjects were positive in their ratings of device cosmetics and ergonomics. The second application is for people with central vision loss. Using an on-axis aligned camera and display system, central visibility is enhanced with 1:1 scale edge images, while still enabling the wide field of the unimpaired peripheral vision to be maintained. The registration error of the system was found to be low in laboratory testing.

Image enhancement of real-time television to benefit the visually impaired

PURPOSE

To examine the use of real-time, generic edge detection, image processing techniques to enhance the television viewing of the visually impaired.

DESIGN

Prospective, clinical experimental study.

METHOD

One hundred and two sequential visually impaired (average age 73.8 +/- 14.8 years; 59% female) in a single center optimized a dynamic television image with respect to edge detection filter (Prewitt, Sobel, or the two combined), color (red, green, blue, or white), and intensity (one to 15 times) of the overlaid edges. They then rated the original television footage compared with a black-and-white image displaying the edges detected and the original television image with the detected edges overlaid in the chosen color and at the intensity selected. Footage of news, an advertisement, and the end of program credits were subjectively assessed in a random order.

RESULTS

A Prewitt filter was preferred (44%) compared with the Sobel filter (27%) or a combination of the two (28%). Green and white were equally popular for displaying the detected edges (32%), with blue (22%) and red (14%) less so. The average preferred edge intensity was 3.5 +/- 1.7 times. The image-enhanced television was significantly preferred to the original (P < .001), which in turn was preferred to viewing the detected edges alone (P < .001) for each of the footage clips. Preference was not dependent on the condition causing visual impairment. Seventy percent were definitely willing to buy a set-top box that could achieve these effects for a reasonable price.

CONCLUSIONS

Simple generic edge detection image enhancement options can be performed on television in real-time and significantly enhance the viewing of the visually impaired.

Recognition performance and perceived quality of video enhanced for the visually impaired

Subjects with central field loss (CFL) individually selected enhancement parameters to improve visibility of static video images. The effect of enhancement on performance and on perceived quality of motion video was assessed. Performance, e.g. recognition of visual details, was assessed by having subjects answer questions regarding visual information contained in the video motion segments that were enhanced using the individually-selected parameters. Enhancement did not improve subject performance on questions about video content. This result might be due to a ceiling effect limitation of the performance assessment method. In a second procedure, subjects' continuous perceptions of quality (using an adjective-based rating scale) were made while the enhancement parameters were abruptly switched among multiple values; these included the individually-selected enhancements, as well as unenhanced, over-enhanced, and degraded segments. The results indicate that adaptive enhancement (individually-tuned using a static image) adds significantly to perceived image quality when viewing motion video. Subjects who selected stronger contrast enhancement also perceived the enhancement to provide a larger benefit in image quality.

Post Transmission Digital Video Enhancement for People with Visual Impairments

Image enhancement has been shown to improve the perceived quality of images and videos for people with visual impairments. The MPEG coding scheme makes spatial filtering, likely to help those with such impairments, possible at the decoding stage. We implemented a real-time platform for testing and improving contrast enhancement algorithms for MPEG video, with controls appropriate for the target population. The necessary additional processing runs efficiently on a general-purpose PC and can be integrated easily into existing MPEG-2 decoders. The system has enabled us to substantially improve the previous filtering algorithm; reducing artifacts exhibited in the previous implementation and should facilitate individual user-selection of enhancement parameters in evaluation studies.