Philippe Colantoni

Regions adjacency graph applied to color image segmentation

The aim of this paper is to present different algorithms, based on a combination of two structures of graph and of two color image processing methods, in order to segment color images. The structures used in this study are the region adjacency graph and the line graph associated.We will see how these structures can enhance segmentation processes such as region growing or watershed transformation. The principal advantage of these structures is that they give more weight to adjacency relationships between regions than usual methods. Let us note nevertheless that this advantage leads in return to adjust more parameters than other methods to best refine the result of the segmentation.We will show that this adjustment is necessarily image dependent and observer dependent.

Virtual Environments with Four or More Spatial Dimensions

We describe methods for displaying complex, texturemapped environments with four or more spatial dimensions that allow for real-time interaction. At any one moment in time, a three-dimensional cross section of the high-dimensional environment is rendered using techniques that have been implemented in OpenGL. The position and orientation of the user within the environment determine the 3-D cross section. A variety of interfaces can be used to control position and orientation in 4-D, including a mouse freelook interface for use with a computer monitor display, and an interface that uses a head-tracking system with three degrees of freedom and PINCH gloves in combination with a head-mounted display. The methods avoid the use of projections that require depth buffering in greater than three dimensions and can be used in conjunction with either 2-D or 3-D texture mapping. A computer graphic engine that displays 4-D virtual environments interactively uses these methods, as does a level editor and modeling program that can be used to create 4-D environments.

An inverse display color characterization model based on an optimized geometrical structure

We have defined an inverse model for colorimetric characterization of additive displays. It is based on an optimized three-dimensional tetrahedral structure. In order to minimize the number of measurements, the structure is defined using a forward characterization model. Defining a regular grid in the device-dependent destination color space leads to heterogeneous interpolation errors in the device-independent source color space. The parameters of the function used to define the grid are optimized using a globalized Nelder-Mead simplex downhill algorithm. Several cost functions are tested on several devices. We have performed experiments with a forward model which assumes variation in chromaticities (PLVC), based on one-dimensional interpolations for each primary ramp along X, Y and Z (3×3×1-D). Results on 4 devices (2 LCD and a DLP projection devices, one LCD monitor) are shown and discussed.

High-end colorimetric display characterization using an adaptive training set

A new, accurate, and technology-independent display color-characterization model is introduced. It is based on polyharmonic spline interpolation and on an optimized adaptive training data set. The establishment of this model is fully automatic and requires only a few minutes, making it efficient in a practical situation. The experimental results are very good for both the forward and inverse models. Typically, the proposed model yields an average model prediction error of about 1 ∆Eab* unit or below for several displays. The maximum error is shown to be low as well. freedom given to the model considering the choice of a tar- get color space and of the kernel and smoothing factor for the interpolation. This increases noticeably the accuracy of the model. The inverse model is based on a tetrahedral in- terpolation, using a grid designed in RGB. As design goals, we aim for the display color-characterization model to be as accurate as possible on any type of display and we want the color correction to be done in real time (no pre-processing). Moreover, we want the model establishment not to exceed a practical time of a few minutes (the time of a coffee break). We first present the state of the art of display color characterization in Sec. 2. We then introduce our new accu- rate display color-characterization model. We evaluate this method experimentally on different displays. Before con- cluding, we describe briefly its application to multispectral image real-time color rendering under a virtual illumination through its GPU implementation.

Visualization of events from arbitrary spacetime perspectives

Methods for representing spacetime events as hyperobjects in 4D space have been developed that let one examine events from arbitrary spacetime perspectives. 3D objects that move either rigidly or nonrigidly are extruded to create 4D hyperobjects. The boundaries of the 4D objects are represented using polyhedra, in much the same way that the boundaries of 3D objects may be represented using polygons. The user views one or more static, 4D hyperobjects using software which lets the user control in an interactive, realtime fashion the position and orientation of a 3D cross- section of the hyperobjects. The 3D cross-sections are rendered using standard techniques of 3D computer graphics. Extrusion of nonrigid 3D objects is useful for visualizing events that involve objects with time-varying shape. For instance, one can use nonrigid extrusion to visualize a character animation, in which multiple frames of a walking humanoid character are used to create a single, static hyperobject that represents the entire animation. With these methods, one need no longer be limited to watching a movie in which time is a hidden axis. Rather, one can view and alter events immersively from arbitrary vantage points.

A Color Management Process for Real Time Color Reconstruction of Multispectral Images

We introduce a new accurate and technology independent display color characterization model for color rendering of multispectral images. The establishment of this model is automatic, and does not exceed the time of a coffee break to be efficient in a practical situation. This model is a part of the color management workflow of the new tools designed at the C2RMF for multispectral image analysis of paintings acquired with the material developed during the CRISATEL European project. The analysis is based on color reconstruction with virtual illuminants and use a GPU (Graphics processor unit) based processing model in order to interact in real time with a virtual lighting.

Hybrid color spaces applied to image database

Many difficulties of color image processing may be resolved using specific color spaces. The problematic when discussing about image database is the same: in which color space a method will be the most effective. We present classical color spaces, and a tool able to represent images in these spaces in order to analyze which color space is the most relevant on the studied images. Secondly we will introduce hybrid color spaces. The basic idea of hybrid color spaces is to combine several color components from different color spaces in order to increase the effectiveness of color components to discriminate color data, and to reduce correlation rate between color components. Generally computed from an unique image we propose an extension of hybrid computation to generate Hybrid color space from image database. The main idea is to use a set of images as a unique image, and to realize statistical computation on this “virtual” image. Finally, we will present a system able to manage hybrid color space generation on images set, using Icobra and ColorSpace tools.

Perception of color change

This article reviews recent work on the perception of color in cases where color change leads to scission, or a perceived layering in depth of the visual field into chromatic processes. A model is proposed that predicts under what circumstances a layering in depth is perceived. The model takes into account shift in color and change in contrast; it helps to describe the colors and lightnesses of surfaces seen through a transparent filter or through fog.

Graph-based 3D Visualization of Color Content in Paintings

Visualization of the color content of a painting can help to better understand the style, compositional structure and material content. There are several ways to visualize colorimetric data from a color image. One option consists of using of 3D Virtual Reality to view colorimetric data in arbitrary orientation in a standard color space. In this paper we propose a new colorimetric visualization method. The originality of this method is that we include spatial organization of colors inside the painting. We can thus visualize information on color gradients that may appear in the painting using simple 3D primitives. We demonstrate the efficiency of our method on a colorimetrically calibrated image of an Italian Renaissance painting.

A geometrical approach for inverting display color-characterization models

— Some display color-characterization models are not easily inverted. This work proposes ways to build geometrical inverse models given any forward color-characterization model. The main contribution is to propose and analyze several methods to optimize the 3-D geometrical structure of an inverse color-characterization model directly based on the forward model. Both the amount of data and their distribution in color space is especially focused on. Several optimization criteria, related either to an evaluation data set or to the geometrical structure itself, are considered. A practical case with several display devices, combining the different methods proposed in the article, are considered and analyzed.