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Author | Ivet Rafegas; Javier Vazquez; Robert Benavente; Maria Vanrell; Susana Alvarez |
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Title | Enhancing spatio-chromatic representation with more-than-three color coding for image description | Type | Journal Article | |||
Year | 2017 | Publication | Journal of the Optical Society of America A | Abbreviated Journal ![]() |
JOSA A | |
Volume | 34 | Issue | 5 | Pages | 827-837 | |
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Abstract | Extraction of spatio-chromatic features from color images is usually performed independently on each color channel. Usual 3D color spaces, such as RGB, present a high inter-channel correlation for natural images. This correlation can be reduced using color-opponent representations, but the spatial structure of regions with small color differences is not fully captured in two generic Red-Green and Blue-Yellow channels. To overcome these problems, we propose a new color coding that is adapted to the specific content of each image. Our proposal is based on two steps: (a) setting the number of channels to the number of distinctive colors we find in each image (avoiding the problem of channel correlation), and (b) building a channel representation that maximizes contrast differences within each color channel (avoiding the problem of low local contrast). We call this approach more-than-three color coding (MTT) to enhance the fact that the number of channels is adapted to the image content. The higher color complexity an image has, the more channels can be used to represent it. Here we select distinctive colors as the most predominant in the image, which we call color pivots, and we build the new color coding using these color pivots as a basis. To evaluate the proposed approach we measure its efficiency in an image categorization task. We show how a generic descriptor improves its performance at the description level when applied on the MTT coding. | |||||
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Notes | CIC; 600.087 | Approved | no | |||
Call Number | Admin @ si @ RVB2017 | Serial | 2892 | |||
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Author | Hassan Ahmed Sial; Ramon Baldrich; Maria Vanrell |
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Title | Deep intrinsic decomposition trained on surreal scenes yet with realistic light effects | Type | Journal Article | |||
Year | 2020 | Publication | Journal of the Optical Society of America A | Abbreviated Journal ![]() |
JOSA A | |
Volume | 37 | Issue | 1 | Pages | 1-15 | |
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Abstract | Estimation of intrinsic images still remains a challenging task due to weaknesses of ground-truth datasets, which either are too small or present non-realistic issues. On the other hand, end-to-end deep learning architectures start to achieve interesting results that we believe could be improved if important physical hints were not ignored. In this work, we present a twofold framework: (a) a flexible generation of images overcoming some classical dataset problems such as larger size jointly with coherent lighting appearance; and (b) a flexible architecture tying physical properties through intrinsic losses. Our proposal is versatile, presents low computation time, and achieves state-of-the-art results. | |||||
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Notes | CIC; 600.140; 600.12; 600.118 | Approved | no | |||
Call Number | Admin @ si @ SBV2019 | Serial | 3311 | |||
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Author | Jordi Roca; C. Alejandro Parraga; Maria Vanrell |
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Title | Chromatic settings and the structural color constancy index | Type | Journal Article | |||
Year | 2013 | Publication | Journal of Vision | Abbreviated Journal ![]() |
JV | |
Volume | 13 | Issue | 4-3 | Pages | 1-26 | |
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Abstract | Color constancy is usually measured by achromatic setting, asymmetric matching, or color naming paradigms, whose results are interpreted in terms of indexes and models that arguably do not capture the full complexity of the phenomenon. Here we propose a new paradigm, chromatic setting, which allows a more comprehensive characterization of color constancy through the measurement of multiple points in color space under immersive adaptation. We demonstrated its feasibility by assessing the consistency of subjects' responses over time. The paradigm was applied to two-dimensional (2-D) Mondrian stimuli under three different illuminants, and the results were used to fit a set of linear color constancy models. The use of multiple colors improved the precision of more complex linear models compared to the popular diagonal model computed from gray. Our results show that a diagonal plus translation matrix that models mechanisms other than cone gain might be best suited to explain the phenomenon. Additionally, we calculated a number of color constancy indices for several points in color space, and our results suggest that interrelations among colors are not as uniform as previously believed. To account for this variability, we developed a new structural color constancy index that takes into account the magnitude and orientation of the chromatic shift in addition to the interrelations among colors and memory effects. | |||||
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Notes | CIC; 600.052; 600.051; 605.203 | Approved | no | |||
Call Number | Admin @ si @ RPV2013 | Serial | 2288 | |||
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Author | Javier Vazquez; C. Alejandro Parraga; Maria Vanrell |
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Title | Ordinal pairwise method for natural images comparison | Type | Journal Article | |||
Year | 2009 | Publication | Perception | Abbreviated Journal ![]() |
PER | |
Volume | 38 | Issue | Pages | 180 | ||
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Abstract | 38(Suppl.)ECVP Abstract Supplement
We developed a new psychophysical method to compare different colour appearance models when applied to natural scenes. The method was as follows: two images (processed by different algorithms) were displayed on a CRT monitor and observers were asked to select the most natural of them. The original images were gathered by means of a calibrated trichromatic digital camera and presented one on top of the other on a calibrated screen. The selection was made by pressing on a 6-button IR box, which allowed observers to consider not only the most natural but to rate their selection. The rating system allowed observers to register how much more natural was their chosen image (eg, much more, definitely more, slightly more), which gave us valuable extra information on the selection process. The results were analysed considering both the selection as a binary choice (using Thurstone's law of comparative judgement) and using Bradley-Terry method for ordinal comparison. Our results show a significant difference in the rating scales obtained. Although this method has been used in colour constancy algorithm comparisons, its uses are much wider, eg to compare algorithms of image compression, rendering, recolouring, etc. |
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Notes | CIC | Approved | no | |||
Call Number | CAT @ cat @ VPV2009b | Serial | 1191 | |||
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Author | Robert Benavente; C. Alejandro Parraga; Maria Vanrell |
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Title | Colour categories boundaries are better defined in contextual conditions | Type | Journal Article | |||
Year | 2009 | Publication | Perception | Abbreviated Journal ![]() |
PER | |
Volume | 38 | Issue | Pages | 36 | ||
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Abstract | In a previous experiment [Parraga et al, 2009 Journal of Imaging Science and Technology 53(3)] the boundaries between basic colour categories were measured by asking subjects to categorize colour samples presented in isolation (ie on a dark background) using a YES/NO paradigm. Results showed that some boundaries (eg green – blue) were very diffuse and the subjects' answers presented bimodal distributions, which were attributed to the emergence of non-basic categories in those regions (eg turquoise). To confirm these results we performed a new experiment focussed on the boundaries where bimodal distributions were more evident. In this new experiment rectangular colour samples were presented surrounded by random colour patches to simulate contextual conditions on a calibrated CRT monitor. The names of two neighbouring colours were shown at the bottom of the screen and subjects selected the boundary between these colours by controlling the chromaticity of the central patch, sliding it across these categories' frontier. Results show that in this new experimental paradigm, the formerly uncertain inter-colour category boundaries are better defined and the dispersions (ie the bimodal distributions) that occurred in the previous experiment disappear. These results may provide further support to Berlin and Kay's basic colour terms theory. | |||||
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Notes | CIC | Approved | no | |||
Call Number | CAT @ cat @ BPV2009 | Serial | 1192 | |||
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Author | C. Alejandro Parraga; Javier Vazquez; Maria Vanrell |
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Title | A new cone activation-based natural images dataset | Type | Journal Article | |||
Year | 2009 | Publication | Perception | Abbreviated Journal ![]() |
PER | |
Volume | 36 | Issue | Pages | 180 | ||
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Abstract | We generated a new dataset of digital natural images where each colour plane corresponds to the human LMS (long-, medium-, short-wavelength) cone activations. The images were chosen to represent five different visual environments (eg forest, seaside, mountain snow, urban, motorways) and were taken under natural illumination at different times of day. At the bottom-left corner of each picture there was a matte grey ball of approximately constant spectral reflectance (across the camera's response spectrum,) and nearly Lambertian reflective properties, which allows to compute (and remove, if necessary) the illuminant's colour and intensity. The camera (Sigma Foveon SD10) was calibrated by measuring its sensor's spectral responses using a set of 31 spectrally narrowband interference filters. This allowed conversion of the final camera-dependent RGB colour space into the Smith and Pokorny (1975) cone activation space by means of a polynomial transformation, optimised for a set of 1269 Munsell chip reflectances. This new method is an improvement over the usual 3 × 3 matrix transformation which is only accurate for spectrally-narrowband colours. The camera-to-LMS transformation can be recalculated to consider other non-human visual systems. The dataset is available to download from our website. | |||||
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Notes | CIC | Approved | no | |||
Call Number | CAT @ cat @ PVV2009 | Serial | 1193 | |||
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Author | C. Alejandro Parraga; Robert Benavente; Maria Vanrell |
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Title | Towards a general model of colour categorization which considers context | Type | Journal Article | |||
Year | 2010 | Publication | Perception. ECVP Abstract Supplement | Abbreviated Journal ![]() |
PER | |
Volume | 39 | Issue | Pages | 86 | ||
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Abstract | In two previous experiments [Parraga et al, 2009 J. of Im. Sci. and Tech 53(3) 031106; Benavente et al,2009 Perception 38 ECVP Supplement, 36] the boundaries of basic colour categories were measured.
In the first experiment, samples were presented in isolation (ie on a dark background) and boundaries were measured using a yes/no paradigm. In the second, subjects adjusted the chromaticity of a sample presented on a random Mondrian background to find the boundary between pairs of adjacent colours. Results from these experiments showed significant dierences but it was not possible to conclude whether this discrepancy was due to the absence/presence of a colourful background or to the dierences in the paradigms used. In this work, we settle this question by repeating the first experiment (ie samples presented on a dark background) using the second paradigm. A comparison of results shows that although boundary locations are very similar, boundaries measured in context are significantly dierent(more diuse) than those measured in isolation (confirmed by a Student’s t-test analysis on the subject’s answers statistical distributions). In addition, we completed the mapping of colour name space by measuring the boundaries between chromatic colours and the achromatic centre. With these results we completed our parametric fuzzy-sets model of colour naming space. |
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Notes | CIC | Approved | no | |||
Call Number | CAT @ cat @ PBV2010b | Serial | 1326 | |||
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Author | Olivier Penacchio; C. Alejandro Parraga; Maria Vanrell |
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Title | Natural Scene Statistics account for Human Cones Ratios | Type | Journal Article | |||
Year | 2010 | Publication | Perception. ECVP Abstract Supplement | Abbreviated Journal ![]() |
PER | |
Volume | 39 | Issue | Pages | 101 | ||
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Abstract | In two previous experiments [Parraga et al, 2009 J. of Im. Sci. and Tech 53(3) 031106; Benavente et al,2009 Perception 38 ECVP Supplement, 36] the boundaries of basic colour categories were measured.
In the first experiment, samples were presented in isolation (ie on a dark background) and boundaries were measured using a yes/no paradigm. In the second, subjects adjusted the chromaticity of a sample presented on a random Mondrian background to find the boundary between pairs of adjacent colours. Results from these experiments showed significant dierences but it was not possible to conclude whether this discrepancy was due to the absence/presence of a colourful background or to the dierences in the paradigms used. In this work, we settle this question by repeating the first experiment (ie samples presented on a dark background) using the second paradigm. A comparison of results shows that although boundary locations are very similar, boundaries measured in context are significantly dierent(more diuse) than those measured in isolation (confirmed by a Student’s t-test analysis on the subject’s answers statistical distributions). In addition, we completed the mapping of colour name space by measuring the boundaries between chromatic colours and the achromatic centre. With these results we completed our parametric fuzzy-sets model of colour naming space. |
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Notes | CIC | Approved | no | |||
Call Number | CAT @ cat @ PPV2010 | Serial | 1357 | |||
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Author | C. Alejandro Parraga; Olivier Penacchio; Maria Vanrell |
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Title | Retinal Filtering Matches Natural Image Statistics at Low Luminance Levels | Type | Journal Article | |||
Year | 2011 | Publication | Perception | Abbreviated Journal ![]() |
PER | |
Volume | 40 | Issue | Pages | 96 | ||
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Abstract | The assumption that the retina’s main objective is to provide a minimum entropy representation to higher visual areas (ie efficient coding principle) allows to predict retinal filtering in space–time and colour (Atick, 1992 Network 3 213–251). This is achieved by considering the power spectra of natural images (which is proportional to 1/f2) and the suppression of retinal and image noise. However, most studies consider images within a limited range of lighting conditions (eg near noon) whereas the visual system’s spatial filtering depends on light intensity and the spatiochromatic properties of natural scenes depend of the time of the day. Here, we explore whether the dependence of visual spatial filtering on luminance match the changes in power spectrum of natural scenes at different times of the day. Using human cone-activation based naturalistic stimuli (from the Barcelona Calibrated Images Database), we show that for a range of luminance levels, the shape of the retinal CSF reflects the slope of the power spectrum at low spatial frequencies. Accordingly, the retina implements the filtering which best decorrelates the input signal at every luminance level. This result is in line with the body of work that places efficient coding as a guiding neural principle. | |||||
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Notes | CIC | Approved | no | |||
Call Number | Admin @ si @ PPV2011 | Serial | 1720 | |||
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Author | Jordi Roca; C. Alejandro Parraga; Maria Vanrell |
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Title | Predicting categorical colour perception in successive colour constancy | Type | Abstract | |||
Year | 2012 | Publication | Perception | Abbreviated Journal ![]() |
PER | |
Volume | 41 | Issue | Pages | 138 | ||
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Abstract | Colour constancy is a perceptual mechanism that seeks to keep the colour of objects relatively stable under an illumination shift. Experiments haveshown that its effects depend on the number of colours present in the scene. We
studied categorical colour changes under different adaptation states, in particular, whether the colour categories seen under a chromatically neutral illuminant are the same after a shift in the chromaticity of the illumination. To do this, we developed the chromatic setting paradigm (2011 Journal of Vision11 349), which is as an extension of achromatic setting to colour categories. The paradigm exploits the ability of subjects to reliably reproduce the most representative examples of each category, adjusting multiple test patches embedded in a coloured Mondrian. Our experiments were run on a CRT monitor (inside a dark room) under various simulated illuminants and restricting the number of colours of the Mondrian background to three, thus weakening the adaptation effect. Our results show a change in the colour categories present before (under neutral illumination) and after adaptation (under coloured illuminants) with a tendency for adapted colours to be less saturated than before adaptation. This behaviour was predicted by a simple affine matrix model, adjusted to the chromatic setting results. |
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ISSN | 0301-0066 | ISBN | Medium | |||
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Notes | CIC | Approved | no | |||
Call Number | Admin @ si @ RPV2012 | Serial | 2188 | |||
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Author | Susana Alvarez; Maria Vanrell |
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Title | Texton theory revisited: a bag-of-words approach to combine textons | Type | Journal Article | |||
Year | 2012 | Publication | Pattern Recognition | Abbreviated Journal ![]() |
PR | |
Volume | 45 | Issue | 12 | Pages | 4312-4325 | |
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Abstract | The aim of this paper is to revisit an old theory of texture perception and
update its computational implementation by extending it to colour. With this in mind we try to capture the optimality of perceptual systems. This is achieved in the proposed approach by sharing well-known early stages of the visual processes and extracting low-dimensional features that perfectly encode adequate properties for a large variety of textures without needing further learning stages. We propose several descriptors in a bag-of-words framework that are derived from different quantisation models on to the feature spaces. Our perceptual features are directly given by the shape and colour attributes of image blobs, which are the textons. In this way we avoid learning visual words and directly build the vocabularies on these lowdimensionaltexton spaces. Main differences between proposed descriptors rely on how co-occurrence of blob attributes is represented in the vocabularies. Our approach overcomes current state-of-art in colour texture description which is proved in several experiments on large texture datasets. |
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ISSN | 0031-3203 | ISBN | Medium | |||
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Notes | CIC | Approved | no | |||
Call Number | Admin @ si @ AlV2012a | Serial | 2130 | |||
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Author | Ivet Rafegas; Maria Vanrell; Luis A Alexandre; G. Arias |
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Title | Understanding trained CNNs by indexing neuron selectivity | Type | Journal Article | |||
Year | 2020 | Publication | Pattern Recognition Letters | Abbreviated Journal ![]() |
PRL | |
Volume | 136 | Issue | Pages | 318-325 | ||
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Abstract | The impressive performance of Convolutional Neural Networks (CNNs) when solving different vision problems is shadowed by their black-box nature and our consequent lack of understanding of the representations they build and how these representations are organized. To help understanding these issues, we propose to describe the activity of individual neurons by their Neuron Feature visualization and quantify their inherent selectivity with two specific properties. We explore selectivity indexes for: an image feature (color); and an image label (class membership). Our contribution is a framework to seek or classify neurons by indexing on these selectivity properties. It helps to find color selective neurons, such as a red-mushroom neuron in layer Conv4 or class selective neurons such as dog-face neurons in layer Conv5 in VGG-M, and establishes a methodology to derive other selectivity properties. Indexing on neuron selectivity can statistically draw how features and classes are represented through layers in a moment when the size of trained nets is growing and automatic tools to index neurons can be helpful. | |||||
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Notes | CIC; 600.087; 600.140; 600.118 | Approved | no | |||
Call Number | Admin @ si @ RVL2019 | Serial | 3310 | |||
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Author | Javier Vazquez; Maria Vanrell; Ramon Baldrich; Francesc Tous |
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Title | Color Constancy by Category Correlation | Type | Journal Article | |||
Year | 2012 | Publication | IEEE Transactions on Image Processing | Abbreviated Journal ![]() |
TIP | |
Volume | 21 | Issue | 4 | Pages | 1997-2007 | |
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Abstract | Finding color representations which are stable to illuminant changes is still an open problem in computer vision. Until now most approaches have been based on physical constraints or statistical assumptions derived from the scene, while very little attention has been paid to the effects that selected illuminants have
on the final color image representation. The novelty of this work is to propose perceptual constraints that are computed on the corrected images. We define the category hypothesis, which weights the set of feasible illuminants according to their ability to map the corrected image onto specific colors. Here we choose these colors as the universal color categories related to basic linguistic terms which have been psychophysically measured. These color categories encode natural color statistics, and their relevance across different cultures is indicated by the fact that they have received a common color name. From this category hypothesis we propose a fast implementation that allows the sampling of a large set of illuminants. Experiments prove that our method rivals current state-of-art performance without the need for training algorithmic parameters. Additionally, the method can be used as a framework to insert top-down information from other sources, thus opening further research directions in solving for color constancy. |
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ISSN | 1057-7149 | ISBN | Medium | |||
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Notes | CIC | Approved | no | |||
Call Number | Admin @ si @ VVB2012 | Serial | 1999 | |||
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Author | Eduard Vazquez; Ramon Baldrich; Joost Van de Weijer; Maria Vanrell |
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Title | Describing Reflectances for Colour Segmentation Robust to Shadows, Highlights and Textures | Type | Journal Article | |||
Year | 2011 | Publication | IEEE Transactions on Pattern Analysis and Machine Intelligence | Abbreviated Journal ![]() |
TPAMI | |
Volume | 33 | Issue | 5 | Pages | 917-930 | |
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Abstract | The segmentation of a single material reflectance is a challenging problem due to the considerable variation in image measurements caused by the geometry of the object, shadows, and specularities. The combination of these effects has been modeled by the dichromatic reflection model. However, the application of the model to real-world images is limited due to unknown acquisition parameters and compression artifacts. In this paper, we present a robust model for the shape of a single material reflectance in histogram space. The method is based on a multilocal creaseness analysis of the histogram which results in a set of ridges representing the material reflectances. The segmentation method derived from these ridges is robust to both shadow, shading and specularities, and texture in real-world images. We further complete the method by incorporating prior knowledge from image statistics, and incorporate spatial coherence by using multiscale color contrast information. Results obtained show that our method clearly outperforms state-of-the-art segmentation methods on a widely used segmentation benchmark, having as a main characteristic its excellent performance in the presence of shadows and highlights at low computational cost. | |||||
Address | Los Alamitos; CA; USA; | |||||
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Publisher | IEEE Computer Society | Place of Publication | Editor | |||
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ISSN | 0162-8828 | ISBN | Medium | |||
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Notes | CIC | Approved | no | |||
Call Number | Admin @ si @ VBW2011 | Serial | 1715 | |||
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