Elzbieta A. Marszalec

Physics-based face database for color research

Most face databases are meant for pattern recognition use. We report the creation of a unique face database which may be used for color-related studies of faces. We describe it as physics- based because it not only contains color images but also data on color image formation such as spectral reflectance measurements from facial skin, illuminant spectral power distribution, and camera spectral response. We demonstrate the usefulness of the database by an approach we developed to color correct face images taken under different illumination conditions.

Accurate color discrimination with classification based on feature distributions

This paper considers a pattern recognition approach to accurate camera-based color measurements. The performances of Swain and Ballards color indexing method based on 3-dimensional histograms and of a simplified version based on three 1-dimensional histograms are evaluated using three common color spaces and two sets of test images.

Making saturated facial images useful again

Saturation here refers to electronic saturation of the camera sensors which produces clipped colors, and not the purity of color as in the hue-saturation and value scale. Saturated images are routinely discarded in image analysis yet there are situations when they cannot be avoided. This paper proposes two strategies to recover color information in facial images taken under non-ideal conditions to make them useful for further processing. The first assumes that the skin is matte and that there are parts of the image which are not clipped. Ratios between R, G and B values of unclipped pixels belonging to the same parts of the image may then be used to compute for lost channel values. The second approach uses color eigenfaces computed from our physics-based face database obtained under different illuminants and camera calibration conditions. Skin color is recovered by transforming the first few eigenface coefficients towards ideal condition values. Excellent color recovery for clipped images is achieved when these two techniques are combined and used on face images captured under daylight illuminant with a camera white balanced for incandescent light.

Online color camera calibration

This paper presents a practical approach to online color camera calibration under changing illumination conditions. Calibration is based on a color camera model and color constancy. In the first stage of the calibration a reconstruction of the current illuminant is performed based on an image taken from a scene with a calibrated color set. Using the updated power spectrum distribution of the current illumination the output camera values are corrected. Based on the corrected camera output values reconstruction of the reflectance spectrum of a random color object is performed and color features of the object can be determined under a required illuminant color temperature. The simulation experiments of the algorithm and results of tests on real images are discussed and the performance of the calibration is evaluated. The approach provides a real time color camera calibration procedure for many applications of machine vision.

SOME ASPECTS OF RGB VISION AND ITS APPLICATIONS IN INDUSTRY

RGB machine vision overlaps both colorimetry instrumentation and gray scale machine vision, and offers advantages over both. Proper calibration of the color camera which makes measurements independent of changes in illumination is essential for the reliability of color machine vision. A practical approach to on-line color camera calibration under unstable illumination conditions is presented and the performance of the procedure is evaluated. New potential applications of RGB machine vision are discussed from the perspective of physics-based vision and the calibration procedure developed here.

Color analysis of defects for automated visual inspection of pine wood

The goal of our research is to develop an automated system for the visual inspection of wood surfaces. Our present approach to inspection is based on the computing of color and texture features for non-overlapping image windows and classifying each window into one of a set of prototype defect classes on the basis of training statistics. The choice of features and final classification strategy nevertheless requires an analysis of the color properties of defects and clear wood. The spectra reflectance characteristics of objects in the visible spectrum were used in the color analysis, these being invariant properties of objects concerned. The analysis was performed for pine wood, employing measurements of the spectral reflectance characteristics of clear wood and visible defects. This enabled a few types of clear wood to be classified in terms of the degree of color homogeneity, defects recognizable against the background of the clear wood and defects differentiable by color. The results indicate that color provides very valuable information for the discrimination of wood defects. Such spectral reflectance characteristics of defects can also be used to formulate the requirements for a machine vision system.

Color measurements based on a color camera

The domain of color camera applications is increasing all time due to recent progress in color machine vision research. Colorimetric measurement tasks are quite complex as the purpose of color measurement is to provide a quantitative evaluation of the phenomenon of colors as perceived by human vision. A proper colorimetric calibration of the color camera system is needed in order to make color a practical tool in machine vision. This paper discuses two approaches to color measurements based on a color camera and includes an overview of practical approaches to color camera calibration under unstable illumination conditions.

On The Application Of Fiber Optics In The Development Of Sensor Systems Of Intelligent Robots

Over the past ten years a significant number of noncommunication uses for optical fibers have arisen. These applications involve the use of optical fibers in sensors. Special fiber optic sensors have also been developed for robotics. The aim of the paper is to present main directions of research on the development of optical fiber sensors for robotics and to show some of their applications. So far various types of optical fiber sensors of proximity, tactile, pressure, slip and colour have been developed. Some of the most interesting solutions are briefly described. Examples of other applications of fiber optics in the sensor system of robots are also given e.g. the use of a noncoherent optical fiber bundle for illumination of a scene, the use of coherent optical fiber bundles in vision systems for transmitting images from a robot gripper to a CCD image sensor placed out of the gripper. The presented review has been done on the basis of proceedings of many international conferences and symposia on robotics, optoelectronics and fiber optics and international journals.

Advances in colour measurement for biomedical applications

Abstract This paper describes recent progress in colour measurement for biomedical applications, with special emphasis on the design of new instruments using various new technologies, and on the benefits of these designs. The biomedical applications of instrumental colorimetry are illustrated with examples of the clinical diagnosis of skin erythema, colour matching in plastic surgery and skin transplantation, and the clinical analysis of blood and urine strip tests.

Non-destructive testing of the quality of naturally white food products

Abstract Results of research on the determination of a method and a system for on-line non-destructive testing of the quality of naturally white materials are presented. Taking into account analysis of the color properties of the material, two methods are proposed: the first is based on calculation of color indices (whiteness, yellowness, and blue reflectance), and the second is based on comparison of the measured reflectance spectra in appropriately selected wavelength ranges. Practical realization of the second sensing method is described using an optical-fiber color sensor. The testing methods presented can be applied for non-destructive on-line inspection of various color products in different industries.