H. Rabal

Diffraction by a Tilted Aperture

The field amplitude diffracted by a tilted aperture, under the Fraunhofer approximation, is investigated. A new coordinate system is found in which the amplitude of the diffracted field is still expressed as the Fourier transform of the aperture. The complex degree of coherence (CDC) originated by a tilted planar source is analysed in a similar way.

Characterization of a paint drying process through granulometric analysis of speckle dynamic patterns

Dynamic speckle patterns are generated by laser light scattering on surfaces that exhibit some kind of activity, due to physical or biological processes. The characterization of this process is carried out by studying the texture changes of auxiliary images: temporal history of the speckle pattern (THSP). The drying process of water borne paint is studied through a method based on mathematical morphology applied to the THSP image processing. It is based on obtaining the granulometry of these images and their characteristic granulometric spectrum. From the granulometric size distribution of each THSP image four parameters are obtained: mean length, standard deviation, asymmetry and kurtosis. These parameters are found to be suitable as texture features. The Mahalanobis distance is calculated between the texture features of the THSP images representative of the temporary stages of the drying process and the features of the final stage or pattern texture. The behavior of the distance function describes satisfactorily the drying process of the water borne paint. The results are compared with other methods. Compared with others, the granulometric method reported in this paper distinguished by its simplicity and easy implementation and can be used to characterize the evolution of any process recorded through dynamic speckles.

Evaluation of speckle-interferometry descriptors to measuring drying-of-coatings

In the industrial process of painting, paint-drying is an important stage because of its high impact in the final result. Its study is of relevance to improve the properties of the resulting coating. Amalvys experiments to measure the speed of drying on surfaces, based on techniques of speckle interferometry, have been used as a starting point in the evaluation of other methods, which allow to measure the process with greater accuracy. Haralicks descriptors have been studied in depth, then filters based on mathematical morphology techniques, a natural complexity measure and, finally, local binary patterns. Measures of speed of drying based on gravimetrical information were obtained and used as a gold standard. The comparison of different techniques was based on their ability to predict its values through a linear regression model. Morphological descriptors showed a low dependance with the sampling time, a desired property. Permutation entropy and local binary patterns evinced similar drying curves, showing a remarkable inflection point, coincident with the passage on the constant drying area to a later state, defined by a slower diffusion of the solvent through the dry coat of the surface. More precise descriptors of drying phenomena have been identified in this study.

Optical image subtraction through speckle modulated by young fringes

Abstract A new method for subtracting images is proposed. It is based on assigning complementary Youngs fringes to the speckles of the common parts of two images. In this way, carrier frequency is cancelled, and “a-posteriori” spatial filtering shows only noncommon parts. Suggestions on applications of the method are briefly commented.

Digital holographic contouring

Abstract A digital contouring technique is proposed and demonstrated. Two alternative set-ups are suggested and the results compared with those obtained using analog holography. They can be used for real time two-beam as well as for multiple-beam interference fringers.

Vibration analysis with young's fringes modulated speckle

Abstract A new method for vibrational analysis is proposed. It is based on the deblurring of time-averaged Youngs fringes inside speckle grains in the image of a vibrational object. A spatial filtered image of the recording of those speckles, modulated by Youngs fringes, shows the loci of points of equal vibratory amplitude.

Stereograms through a speckle carrier

A new method for registering stereograms in which an orientated speckle pattern supplies the desired directivity for obtaining horizontal parallax is presented. This is accomplished by employing an optical system whose pupil consists of a double-fan aperture. In this way, the stereogram has a built-in reconstruction mechanism, and the stereo image can be observed with almost any extended white light source and without using any optical device. Furthermore, more than two points of view of the 3-D scene can be stored in a single plate by adequate positioning of the above-mentioned aperture.

Real-time white light pseudocolor density encoder

Abstract A simple method for pseudocolor encoding of gray level information is proposed. It is based on the real-time addition of the positive and negative images of an object transparency, each one obtained in a different color. Conventional white light lamps with adequate color filters are used. Some experimental results are shown.

Dynamic laser speckle: decision models with computational intelligence techniques

This paper proposes the design of decision models with Computational Intelligence techniques using image sequences of dynamic laser speckle. These models aim to characterize the dynamic of the process evaluated through Temporal History Speckle Patterns (THSP) using a set of available descriptors. The models use those sets selected to improve its effectiveness, depending on the specific application. The techniques of computational intelligence field include using Artificial Neural Networks, Fuzzy Granular Computation, Evolutionary Computation elements such as Genetic Algorithms, among others. The results obtained in experiments such as the evaluation of bacterial chemotaxis, and the estimation of the drying time of coatings are encouraging and significantly improve those obtained using a single descriptor.

Biospeckle descriptors: a performance comparison

Biospeckle patterns are named also boiling speckles due to its dynamic appearance. This activity takes place when the sample changes its properties due to diverse causes. This phenomenon is characteristic of biological samples and of the some industrial process. There are many descriptors that have been developed to characterize biospeckle patterns. This paper presents some approaches to compare and evaluate a set of time domain descriptors using a controlled experiment.