Modeling Perceptual Color Differences by Local Metric Learning

International audienceHaving perceptual differences between scene colors is key in many computer vision applications such as image segmentation or visual salient region detection. Nevertheless, most of the times, we only have access to the rendered image colors, without any means to go back to the true scene colors. The main existing approaches propose either to compute a perceptual distance between the rendered image colors, or to estimate the scene colors from the rendered image colors and then to evaluate perceptual distances. However the first approach provides distances that can be far from the scene color differences while the second requires the knowledge of the acquisition conditions that are unavailable for most of the applications.In this paper, we design a new local Mahalanobis-like metric learning algorithm that aims at approximating a perceptual scene color difference that is invariant to the acquisition conditions and computed only from rendered image colors. Using the theoretical framework of uniform stability, we provide consistency guarantees on the learned model. Moreover, our experimental evaluation shows its great ability (i) to generalize to new colors and devices and (ii) to deal with segmentation tasks

Desenvolvimento de frutos de cirigueleira (Spondias purpurea L.) Development of red mombin fruits (Spondias purpurea L.)

O objetivo dessa pesquisa foi avaliar a curva de desenvolvimento de frutos da cirigueleira. Para a avaliação do crescimento e maturação, as flores foram marcadas após a antese, e as colheitas dos frutos foram realizadas durante todo o período de desenvolvimento, visando às avaliações de diâmetro, comprimento, peso fresco, peso seco e volume. O ciclo de desenvolvimento da antese até o amadurecimento do fruto foi de 124 dias, sendo caracterizado pelo aumento dos pesos fresco e seco, volume, comprimento e diâmetro. O aumento do comprimento do fruto apresentou maior taxa de crescimento até aproximadamente 55 dias, seguido por um período de crescimento mais lento até 105 dias após a antese. O início da maturação do fruto ocorreu quando a taxa de crescimento foi mais lenta, em torno de 100 dias, enquanto o amadurecimento se iniciou aproximadamente aos 119 dias após a antese.<br>The aim of this research was to evaluate the development profile of red mombin fruits. For the evaluation of growth and maturation, open flowers were marked after anthesis and fruits were sampled at regular intervals, and length, diameter, volume, and, fresh and dry weights were measured throughout the development following the growth of the fruits. Red mombin fruit developmental cycle, from anthesis to full ripening, lasted 124 days, characterized by the increase in fresh and dry weights, volume, length, and diameter. The growth period, mainly characterized by the increase in fruit length, had the highest growth rate until approximately 55 days, followed by a lower growth rate period from 55 to 105 days post-anthesis. Fruit maturation, which started when fruit growth rates slowed down, was set around 100 days and fruit ripening was initiated around 119 days post-anthesis