Manuel M. Oliveira

Universidade Federal do Rio Grande do Sul | UFRGS · Institute of Informatics

We present a technique for real-time adjustment of spatial frequencies in images and videos. Our method allows for both decreasing and increasing of frequencies, and is orthogonal to image resizing. Thus, it can be used to automatically adjust spatial frequencies to preserve the appearance of structured patterns during image downscaling and upscali...

We present a technique for synthesizing realistic noise for digital photographs. It can adjust the noise level of an input photograph, either increasing or decreasing it, to match a target ISO level. Our solution learns the mappings among different ISO levels from unpaired data using generative adversarial networks. We demonstrate its effectiveness...

We introduce a technique to synthetically increase the framerate of semi-repetitive videos (i.e., videos of motion that repeats but not in an identical fashion) to aid in visualization. By reordering and combining frames from all repetitions, we produce a single non-repetitive sequence with much higher temporal resolution. Then, we use a novel fram...

In this paper we use a simplified model of the human visual system to explain why humans tend do prefer “sharpened” digital images. From this model we then derive a family of image prefilters specifically adapted to viewing conditions and user preference, allowing for the trade‐off between ringing and aliasing while maximizing image sharpness. We d...

Automatic detection of planar regions in point clouds is an important step for many graphics, image processing, and computer vision applications. While laser scanners and digital photography have allowed us to capture increasingly larger datasets, previous approaches for planar region detection are computationally expensive, precluding their use in...

High-dimensional filters are a fundamental building block for several applications, having recently received considerable attention from the research community. Unfortunately, naive implementations of such an important class of filters are too slow for many practical uses. This dissertation describes three novel approaches to efficiently perform hi...

Cylinder detection is an important step in reverse engineering of industrial sites, as such environments often contain a large number of cylindrical pipes and tanks. However, existing techniques for cylinder detection require the specification of several parameters which are difficult to adjust because their values depend on the noise level of the...

Plane detection is a key component for many applications, such as industrial reverse engineering and self-driving cars. However, existing plane-detection techniques are sensitive to noise and to user-defined parameters. We introduce a fast deterministic technique for plane detection in unorganized point clouds that is robust to noise and virtually...

Despite considerable advances in natural image matting over the last decades, video matting still remains a difficult problem. The main challenges faced by existing methods are the large amount of user input required, and temporal inconsistencies in mattes between pairs of adjacent frames. We present a temporally‐coherent matte‐propagation method f...

The evolution of cancer is inferred mainly from samples taken at discrete points that represent glimpses of the complete process. In this study, we present esiCancer as a cancer-evolution simulator. It uses a branching process, randomly applying events to a diploid oncogenome, altering probabilities of proliferation and death of the affected cells....

Campimetry is an important test to detect and monitor central and peripheral ocular dysfunctions, which might indicate the existence of serious conditions such as glaucoma, or the occurrence of strokes or brain tumors. Commercially-available campimeters are expensive and lack portability. We present a portable, low-cost, easy-to-manufacture smartph...

Although many adaptive sampling and reconstruction techniques for Monte Carlo (MC) rendering have been proposed in the last few years, the case for which one should be used for a specific scene is still to be made. Moreover, developing a new technique has required selecting a particular rendering system, which makes the technique tightly coupled to...

We present a convolutional neural network architecture for performing joint design of color filter array (CFA) patterns and demosaicing. Our generic model allows the training of CFAs of arbitrary sizes, optimizing each color filter over the entire RGB color space. The patterns and algorithms produced by our method provide high-quality color reconst...

We present an image downscaling technique capable of appropriately representing high-frequency structured patterns. Our method breaks conventional wisdom in sampling theory---instead of discarding high-frequency information to avoid aliasing, it controls aliasing by remapping such information to the representable range of the downsampled spectrum....

We present a practical solution to the problem of subject relighting in paintings and drawings. Our interactive technique uses 3-D shading proxies and can be applied to objects with arbitrary geometries. Given a user-provided guess for the shading of an object in a painting/drawing and its corresponding target shading, we refine them using shading-...

We present a practical approach for personalized simulation and objective validation of the effects of low-order aberrations (i.e., myopia, hyperopia and astigmatism) on optical systems, such as the human eye. We characterize the optical aberrations using a wavefront aberration function derived from one's eyeglasses or contact lenses prescription d...

Fluid animation methods based on Eulerian grids have long struggled to resolve flows involving narrow gaps and thin solid features. Past approaches have artificially inflated or voxelized boundaries, although this sacrifices the correct geometry and topology of the fluid domain and prevents flow through narrow regions. We present a boundary-respect...

The field of image composition is constantly trying to improve the ways in which an image can be altered and enhanced. While this is usually done in the name of aesthetics and practicality, it also provides tools that can be used to maliciously alter images. In this sense, the field of digital image forensics has to be prepared to deal with the inf...

Image compositing aims to combine elements from multiple images producing natural-looking results. The Poisson-image-editing framework can generate seamless compositions, but tends to introduce color changes in the inserted elements, which may generate unrealistic and unpleasing results. Recently, Henz et al. have proposed an approach for controlli...

Digital images are ubiquitous in our modern lives, with uses ranging from social media to news, and even scientific papers. For this reason, it is crucial evaluate how accurate people are when performing the task of identify doctored images. In this paper, we performed an extensive user study evaluating subjects capacity to detect fake images. Afte...

Background Retinal arterial narrowing is associated with higher office blood pressure (BP) and ambulatory blood pressure monitoring, and increased incidence of cardiovascular disease, but it is still unknown if the vessel caliber is associated with BP measured at the time of retinography acquisition. Methods Retinal arteriolar and venular calibers...

We present an efficient technique for modeling and rendering complex surface details defined at multiple scales. Conceptually, meta-relief texture mapping can be described as recursively mapping finer relief-texture layers on top of coarser ones. Such a factorization has several desirable properties. For instance, it provides a way of simulating hi...

Image compositing aims to combine elements from multiple images producing natural-looking results. The Poisson image editing framework can generate seamless compositions, but tends to introduce color changes in the inserted objects, which may generate unrealistic and unpleasing results. We present an efficient approach for controlling the amount of...

Automatic detection of planar regions in point clouds is an important step for many graphics, image processing, and computer vision applications. While laser scanners and digital photography have allowed us to capture increasingly larger datasets, previous techniques are computationally expensive, being unable to achieve real-time performance for d...

We present a practical solution to the problem of subject relighting in paintings and drawings. Our interactive technique uses 3-D shading proxies and can be applied to objects with arbitrary geometries. Given a user-provided guess for the shading of an object in a painting/drawing and its corresponding target shading , we refine them using shading...

We describe a technique to generate imagery with improved sharpness for individuals having refractive vision problems. Our method can reduce their dependence on corrective eyewear. It also benefits individuals with normal vision by improving visual acuity at a distance and of small details. Our approach does not require custom hardware. Instead, th...

We present a discrete-time mathematical formulation for applying recursive digital filters to non-uniformly sampled signals. Our solution presents several desirable features: it preserves the stability of the original filters; is well-conditioned for low-pass, high-pass, and band-pass filters alike; its cost is linear in the number of samples and i...

Image compositing aims to combine elements from multiple images producing natural-looking results. The Poisson-image-editing framework can generate seamless compositions, but tends to introduce color changes in the inserted objects, which may generate unrealistic and unpleasing results. We present an efficient approach for controlling the amount of...

We introduce a new interface for augmenting e-learning videos with panoramic frames and content-based navigation. Our interface gradually builds a panoramic video, and allows users to navigate through such video by directly clicking on its contents, as opposed to using a conventional time slider. We demonstrate the effectiveness of our approach by...

The goal of visualization is to effectively and accurately communicate data. Visualization research has often overlooked the errors and uncertainty which accompany the scientific process and describe key characteristics used to fully understand the data. The lack of these representations can be attributed, in part, to the inherent difficulty in def...

Color vision deficiency (CVD) affects a large number of individuals around the world, compromising their ability to effectively interpret color-coded information. This directly impacts the way these individuals perceive visualizations, often introducing ambiguities and uncertainties. This article provides an overview of the causes of color vision d...

Reverse-tone-mapping operators (rTMOs) enhance low-dynamic-range images and videos for display on high-dynamic-range monitors. A common problem faced by previous rTMOs is the handling of under or overexposed content. Under such conditions, they may not be effective, and even cause loss and reversal of visible contrast. We present an rTMO based on c...

In exemplary implementations, this invention is a tool for subjective assessment of the visual acuity of a human eye. A microlens or pinhole array is placed over a high-resolution display. The eye is brought very near to the device. Patterns are displayed on the screen under some of the lenslets or pinholes. Using interactive software, a user cause...

We present an efficient approach for high-quality non-blind deconvolution based on the use of sparse adaptive priors. Its regularization term enforces preservation of strong edges while removing noise. We model the image-prior deconvolution problem as a linear system, which is solved in the frequency domain. This clean formulation lends to a simple...

We present an efficient approach for performing smoke simulation on curvilinear grids. Our technique is based on a fast unconditionally-stable advection algorithm and on a new and efficient solution to enforce mass conservation. It uses a staggered-grid variable arrangement, and has linear cost on the number of grid cells. Our method naturally inte...

Various techniques can be used to improve visualization experiences for individuals with color vision deficiency, including recoloring, pattern superposition, and the use of a color-perception simulation model for assisting visualization designers.

Objective: Abnormalities in retinal vessels are frequent, but its association with findings in other vascular sites has been scarcely investigated. This study aimed to examine the association between ultrasound-measured carotid intima-media thickness (IMT) and retinal arteriolar and venular diameters, in hypertensive patients. Methods: In this c...

Several cellular mechanisms affect nuclear morphology which can therefore be used to assess certain processes. Here, we present an analytic tool to quantify the number of cells in a population that present characteristics of senescence, apoptosis or nuclear irregularities through nuclear morphometric analysis. The tool presented here is based on nu...

Dynamic nuclear condensation measured by NMA. HeLa cells were treated with cisplatin (40 µM) for 18 h. At this time, the same fields were photographed every hour, during 5 hours. (A) NMA of three consecutive measurements one hour apart. Left: normal nuclei; right: apoptotic nuclei. Numbers correspond to the nuclei in (B). (B) Phase contrast and flu...

Supporting Results. This file contains details of the development of the NMA tool and a detailed comparison between Image J and IPP software. (DOC)

NMA of HeLa cells treated with cisplatin or etoposide. HeLa cells were treated with DMSO as vehicle control, cisplatin (40 µM) or etoposide (100 µM) [17], for 24 h, followed by fixation and image acquisition. (A) Overlaid images of cells (visible) and DAPI-stained nuclei. SR – small and regular nucleus; S – small nucleus; N – normal nucleus. (B) NM...

NMA of colon cancer cells treated with vincristine. HCT116 colon cancer cells were treated with DMSO as a vehicle control (A) or vincristine 50 nM (B) for 24 h. Numbers in boxes denote the percentage of nuclei in each category as indicated and averaged area and NII for LR and LI nuclei. (TIF)

NMA of published MC nuclei. Images of normal and MC cells from published papers were analyzed using NMA [1], [14]. (TIF)

Supporting Methods. This file describes the instructions of using Image J, IPP and Spreadsheets to perform the NMA analysis. (DOC)

The Computer Graphics and Interaction group at UFRGS has a well-established tradition of working in the subject of interactive visualization. With publications in the main venues of the field, such as the IEEE Visualization and Eurovis conferences, or journals such as IEEE TVCG (Transactions on Visualization and Computer Graphics) and Computer Grap...

We introduce tailored displays that enhance visual acuity by decomposing virtual objects and placing the resulting anisotropic pieces into the subject's focal range. The goal is to free the viewer from needing wearable optical corrections when looking at displays. Our tailoring process uses aberration and scattering maps to account for refractive e...

We present a technique for performing high-dimensional filtering of images and videos in real time. Our approach produces high-quality results and accelerates filtering by computing the filter’s response at a reduced set of sampling points, and using these for interpolation at all N input pixels. We show that for a proper choice of these sampling p...

We present a coded-aperture method based on a family of masks obtained as the convolution of one “hole” with a structural component consisting of an arrangement of Dirac delta functions. We call the arrangement of delta functions the structural component of the mask, and use it to efficiently encode scene distance information. We illustrate the pot...

Color is one of the most common ways to convey information in visualization applications. Color vision deficiency (CVD) affects approximately 200 million individuals worldwide and considerably degrades their performance in understanding such contents by creating red-green or blue-yellow ambiguities. While several content-specific methods have been...

The Computer Graphics, Image Processing and Interaction (CGIP) group at UFRGS concentrates expertise from many different and complementary graphics related domains. In this paper we introduce the group and present our re- search lines and some ongoing projects. We selected mainly the projects related to 3D interaction and navigation, which includes...

Computational photography tries to expand the concept of traditional photography (a static two dimensional projection of a scene) using state-of-the-art technology. While this can be achieved by combining information from multiple conventional pictures, a more interesting challenge consists in encoding and recovering additional information from one...

Stochastic transparency provides a unified approach to order-independent transparency, antialiasing, and deep shadow maps. It augments screen-door transparency using a random sub-pixel stipple pattern, where each fragment of transparent geometry covers ...

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...

We present a new approach for performing high-quality edge-preserving filtering of images and videos in real time. Our solution is based on a transform that defines an isometry between curves on the 2D image manifold in 5D and the real line. This transform preserves the geodesic distance between points on these curves, adaptively warping the input...

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...

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...

We describe an optical design that retrofits a cell phone display and an interactive software for assessing refractive properties of human eyes. User evaluation revels an average error of ~0.5 diopters using currently available phones.

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 di...

We present an automatic image-recoloring technique for enhancing color contrast for dichromats whose computational cost varies linearly with the number of input pixels. Our approach can be efficiently implemented on GPUs, and we show that for typical image sizes it is up to two orders of magnitude faster than the current state-of-the-art technique....

Abstract Image matting aims at extracting foreground elements from an image by means of color and opacity (alpha) estimation. While a lot of progress has been made in recent years on improving the accuracy of matting techniques, one common problem persisted: the low speed of matte computation. We present the first real-time matting technique for na...

In the above titled paper (ibid., vol. 15, no. 6, pp. 1291-1298, Nov./Dec. 09), there were typos in equations (17) and (18). The correct versions are presented here.

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 di...

Implicit methods are the most popular approach for surface reconstruction from unorganized points. While these methods are very effective for reconstructing closed surfaces, current implicit methods have not ad-dressed the issue of reconstructing surfaces with boundaries. This paper presents an algorithm for reconstructing implicit surfaces with bo...

Color vision deficiency (CVD) affects approximately 200 million people worldwide, compromising the ability of these individuals to effectively perform color and visualization-related tasks. This has a significant impact on their private and professional lives. We present a physiologically-based model for simulating color vision. Our model is based...

Geometric problems in visual computing (computer graphics, computer vision, and image processing) are typically modeled and solved using linear algebra (LA). Thus, vectors are used to represent directions and points in space, while matrices are used to model transformations. LA, however, presents some well-known limitations for performing geometric...