Paulo Daniel Araújo Pinto

Visual sensitivity to color errors in images of natural scenes

Simple color-difference formulae and pictorial images have traditionally been used to estimate the visual impact of color errors introduced by image-reproduction processes. But the limited gamut of RGB cameras constrains such analyses, particularly of natural scenes. The purpose of this work was to estimate visual sensitivity to color errors introduced deliberately into pictures synthesized from hyperspectral images of natural scenes without gamut constraints and to compare discrimination thresholds expressed in CIELAB and S-CIELAB color spaces. From each original image, a set of approximate images with variable color errors were generated and displayed on a calibrated RGB color monitor. The threshold for perceptibility of the errors was determined in a paired-comparison experiment. In agreement with previous studies, it was found that discrimination between original and approximate images needed on average a CIELAB color difference DeltaEab* of about 2.2. Although a large variation of performance across the nine images tested was found when errors were expressed in CIELAB units, little variation was obtained when they were expressed in S-CIELAB units.

Free Typed Text Using Keystroke Dynamics for Continuous Authentication

Information is increasingly in a digital-only format and almost everything we do nowadays depends on a digital identity for authentication and authorization. No matter how strong the authentication system is, after the authentication phase, there is no continuous verification that user is still the same human being that successfully logged in, thus leaving the system unprotected. This paper presents a usable breakthrough approach for continuous authentication with free typed text through the use of biometric techniques based on keystroke dynamics. Our main purpose is to achieve a reduction of the required sample size, while improving (or at least not worsen) precision performance, by adapting and improving parameters on a keystroke dynamics algorithm.

Process Development for Manufacturing of Cellular Structures with Controlled Geometry and Properties

This study presents experimental results on the behaviour of aluminium alloy metal structures and foams manufactured by lost-wax casting and using 3D printed components for internal structure definition. Results for tensile tests, metallurgical properties, surface quality and geometry tolerances were obtained and discussed. The analysis focused on development geometries, used for adjusting manufacturing parameters and prototype geometries intended for geometrical and mechanical validation. The results are indicative of the viability of the method for producing foam structures suitable for mechanical loading.