We have developed a mobile vision assistive device based on a head mounted display (HMD) with a video camera,
which provides image magnification and contrast enhancement for patients with central field loss (CFL). Because the
exposure level of the video camera is usually adjusted according to the overall luminance of the scene, the contrast of
sub-images (to be magnified) may be low. We found that at high magnification levels, conventional histogram
enhancement methods frequently result in over- or under-enhancement due to irregular histogram distribution of subimages.
Furthermore, the histogram range of the sub-images may change dramatically when the camera moves, which
may cause flickering. A piece-wise histogram stretching method based on a center emphasized histogram is proposed
and evaluated by observers. The center emphasized histogram minimizes the histogram fluctuation due to image changes
near the image boundary when the camera moves slightly, which therefore reduces flickering after enhancement. A
piece-wise histogram stretching function is implemented by including a gain turnaround point to deal with very low
contrast images and reduce the possibility of over enhancement. Six normally sighted subjects and a CFL patient were
tested for their preference of images enhanced by the conventional and proposed methods as well as the original images.
All subjects preferred the proposed enhancement method over the conventional method.
Purpose: Patients with tunnel vision have great difficulties in mobility. We have developed an augmented vision head
mounted device, which can provide patients 5x expanded field by superimposing minified edge images of a wider field
captured by a miniature video camera over the natural view seen through the display. In the minified display, objects
appear closer to the heading direction than they really are. This might cause users to overestimate collision risks, and
therefore to perform unnecessary obstacle-avoidance maneuvers. A study was conducted in a virtual environment to test
the impact of minified view on collision judgment.
Methods: Simulated scenes were presented to subjects as if they were walking in a shopping mall corridor. Subjects
reported whether they would make any contact with stationary obstacles that appeared at variable distances from their
walking path. Perceived safe passing distance (PSPD) was calculated by finding the transition point from reports of yes
to no. Decision uncertainty was quantified by the sharpness of the transition. Collision envelope (CE) size was calculated
by summing up PSPD for left and right sides. Ten normally sighted subjects were tested (1) when not using the device
and with one eye patched, and (2) when the see-through view of device was blocked and only minified images were
visible.
Results: The use of the 5x minification device caused only an 18% increase of CE (13cm, p=0.048). Significant impact
of the device on judgment uncertainty was not found (p=0.089).
Conclusion: Minification had only a small impact on collision judgment. This supports the use of such a minifying
device as an effective field expander for patients with tunnel vision.
Conventional RGB color filter array (CFA) in single-chip color cameras greatly reduce light intensity, and therefore
limits the ISO speed of cameras. A novel CFA and an algorithm of forming color images are proposed. 75% of the CFA
are transparent elements, and the remaining 25% are repeated color filter blocks. A compact arrangement of color filter
elements in each block helps to reduce color artifacts. Such an arrangement features a higher sampling rate of luminance
and a lower sampling rate of chrominance.
Black-and-white images (BI) with high resolution can be acquired from the transparent elements, and color images (CI)
with low resolution from the color filter blocks. To generate output color images (OI), the CI in RGB format is
transformed into CIE Lab space, and the luminance components are replaced with the high-resolution BI.
Based on a principle compatible to JPEG format, the visual quality of OI is satisfactory. Simulation was conducted using
raw images acquired with a Canon 20D camera. Results show the potential of the CFA in making digital cameras with
high ISO speed. Applications can be security day/night cameras and cell phone cameras that are able to capture images
with low noise under dim light levels.
An optical see-through head-mounted display (HMD) system integrating a miniature camera that is aligned with the user's pupil is developed and tested. Such an HMD system has a potential value in many augmented reality applications, in which registration of the virtual display to the real scene is one of the critical aspects. The camera alignment to the user's pupil results in a simple yet accurate calibration and a low registration error across a wide range of depth. In reality, a small camera-eye misalignment may still occur in such a system due to the inevitable variations of HMD wearing position with respect to the eye. The effects of such errors are measured. Calculation further shows that the registration error as a function of viewing distance behaves nearly the same for different virtual image distances, except for a shift. The impact of prismatic effect of the display lens on registration is also discussed.
Automated analysis of vessel morphology is valuable in diagnosis since it can provide measurable abnormalities in diameter and tortuosity that reflect systemic or local ocular disease. Although the center point of vessel can be easily detected with matched filter, the diameter cannot be obtained from the readily available convolution result in the process of location detection. An amplitude modified second-order Gaussian filter is presented in this paper. Simulation shows that a profile of vessel matches only one amplitude modified second-order Gaussian filter, with which the convolution peak reaches its maximum. Therefore, the width specified parameter of vessel model can be figured out by matching operation with a group of modified Gaussian filters. A vessel diameter measurement concept based on calibration is presented in order to avoid the burden of finding the exact edges of vessels, which has caused several different width definitions for the endless Gaussian curve. The real vessel width can be determined simply according to the relationship built through a calibration procedure in advance after the width specified parameter of Gaussian curve is obtained. Experiments of blood vessel detection of color fundus image are given. The results of the vessel diameter measurement show good agreement with visual inspection.
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