Vitor Pamplona

Photorealistic models for pupil light reflex and iridal pattern deformation

We introduce a physiologically-based model for pupil light reflex (PLR) and an image-based model for iridal pattern deformation. Our PLR model expresses the pupil diameter as a function of the lighting of the environment, and is described by a delay-differential equation, naturally adapting the pupil diameter even to abrupt changes in light conditions. Since the parameters of our PLR model were derived from measured data, it correctly simulates the actual behavior of the human pupil. Another contribution of our work is a model for realistic deformation of the iris pattern as a function of pupil dilation and constriction. Our models produce high-fidelity appearance effects and can be used to produce real-time predictive animations of the pupil and iris under variable lighting conditions. We assess the predictability and quality of our simulations through comparisons of modeled results against measured data derived from experiments also described in this work. Combined, our models can bring facial animation to new photorealistic standards.

NETRA: interactive display for estimating refractive errors and focal range

We introduce an interactive, portable, and inexpensive solution for estimating refractive errors in the human eye. While expensive optical devices for automatic estimation of refractive correction exist, our goal is to greatly simplify the mechanism by putting the human subject in the loop. Our solution is based on a high-resolution programmable display and combines inexpensive optical elements, interactive GUI, and computational reconstruction. The key idea is to interface a lenticular view-dependent display with the human eye in close range - a few millimeters apart. Via this platform, we create a new range of interactivity that is extremely sensitive to parameters of the human eye, like refractive errors, focal range, focusing speed, lens opacity, etc. We propose several simple optical setups, verify their accuracy, precision, and validate them in a user study.

CATRA: interactive measuring and modeling of cataracts

We introduce an interactive method to assess cataracts in the human eye by crafting an optical solution that measures the perceptual impact of forward scattering on the foveal region. Current solutions rely on highly-trained clinicians to check the back scattering in the crystallin lens and test their predictions on visual acuity tests. Close-range parallax barriers create collimated beams of light to scan through sub-apertures, scattering light as it strikes a cataract. User feedback generates maps for opacity, attenuation, contrast and sub-aperture point-spread functions. The goal is to allow a general audience to operate a portable high-contrast light-field display to gain a meaningful understanding of their own visual conditions. User evaluations and validation with modified camera optics are performed. Compiled data is used to reconstruct the individuals cataract-affected view, offering a novel approach for capturing information for screening, diagnostic, and clinical analysis.

Computer-assisted methods to evaluate retinal vascular caliber: what are they measuring?

PURPOSE Computer-assisted methods to measure retinal vessel diameters have been incorporated into research, but it is not clear which component of the vessels they are measuring. This study was conducted to compare measurements of retinal vessel diameter by using imaging-processing software on color fundus photographs (FPs) and fluorescein angiographs (FAs). METHODS FP and FA images were taken simultaneously in 52 eyes of 31 patients referred for angiography for diagnosis of retinal disease. Arteriolar and venular calibers were measured in two concentric zones around the optic disc center. Pearson correlation coefficients and Bland-Altman plots were used to evaluate the agreement between the measurements made by FP and FA. RESULTS The differences between the diameters measured by the microdensitometric method from FP and FA were 2.59 ± 8.67 μm in the inner arteriola, 4.93 ± 7.47 μm in the outer arteriola, -1,58 ± 8.49 μm in the inner venula, and -1.80 ± 7.28 μm in the outer venula. The differences plotted by the Bland-Altman method were slight. The Pearson correlation coefficients of measurements by FP and FA were 0.84 for inner zone and 0.87 for outer zone arterioles and 0.93 and 0.94 for the inner and outer zone venules, respectively. CONCLUSIONS The very slight differences between measurements of retinal vessel diameter by the two methods demonstrate that the microdensitometric method mostly measures the vessel lumen. Differences in vessel diameters measured by the microdensitometric method observed in clinical conditions may therefore be ascribed to variation in wall thickness or vasoconstriction.

Legolizer: A Real-Time System for Modeling and Rendering LEGO Representations of Boundary Models

In this work we propose a method for converting triangular meshes into LEGO bricks through a voxel representation of boundary meshes. We present a novel voxelization approach that uses points sampled from a surface model to define which cubes (voxels) and their associated colors will compose the model. All steps of the algorithm were implemented on the GPU and real-time performance was achieved with satisfactory volumetric resolutions. Rendering results are illustrated using realistic graphics techniques such as screen space ambient occlusion and irradiance maps.

High-order Power Map and Low-order Lensmeter using a Smartphone Add-on

We developed a portable, low-cost, accurate, wavefront sensing lensmeter for optometry applications: the Netrometer. In addition to low-order measurements (SPH, CYL and AXIS), Netrometer portraits in real-time a power map of the perceived refractive values.

NETRA-G: Towards a Subjective Self-Refraction

We discuss NETRA-Gs sphero-cylindrical self-refractions for teenagers. NETRA-G achieved accuracies of .48D on sphere and .30D on cylinder. Visual acuity was 20/20 or better in 70% of all cases and 20/25 or better for 90%

A conceptual image-based data glove for computer-human interaction

Data gloves are devices equipped with sensors that capture the movements of the hand of the user in order to select or manipulate objects in a virtual world. Data gloves were introduced three decades ago and since then have been used in many 3D interaction techniques. However, good data gloves are too expensive and only a few of them can perceive the full set of hand movements. In this paper we describe the design of an image-based data glove (IBDG) prototype suitable for finger sensible applications, like virtual objects manipulation and interaction approaches. The proposed device uses a camera to track visual markers at finger tips, and a software module to compute the position of each finger tip and its joints in real-time. To evaluate our concept, we have built a prototype and tested it with 15 volunteers. We also discuss how to improve the engineering of the prototype, how to turn it into a low cost interaction device, as well as other relevant issues about this original concept.