Nelly Cap

Display of local activity using dynamical speckle patterns

We present a display to distinguish loci of equal activity in samples showing dynamic speckle patterns. Regions differing in their activity are shown as different gray levels. We define the generalized differences and the weighted generalized difference operations and we compare the results with previously reported methods. Results obtained with seeds are shown.

Bio-speckle assessment of bruising in fruits

The dynamic speckle patterns or bio-speckle is a phenomenon produced by laser illumination of active materials, such as a biological tissue. Fruits, even hard peel ones, show a speckle activity that can be related to maturity, turgor, damage, aging, and mechanical properties. In this case, we suggest a bio-speckle technique as a potential methodology for the study of impact on apples and the analysis of bruises produced by them. The aim is to correlate physical properties of apples with quality factors using a non-contact and non-invasive technique.

Transient phenomena analysis using dynamic speckle patterns

The full width at half maximum (FWHM) is sometimes used to characterize the autocorrelation function of the time history of a speckle pattern. We propose to include more autocorrelation points to diminish the variability of the measurement. The width of the equivalent rectangle (WER) and the X*LOG X measurements are defined and some simulations and experimental results obtained are shown.

Numerical model for dynamic speckle: an approach using the movement of the scatterers

Dynamic speckle or biospeckle is a phenomenon generated by laser light scattering in biological tissues and it is also present in some industrial processes where the surfaces exhibit some kind of activity. In this work we present some results of a numerical model to describe the time history of a dynamic speckle pattern considering very simplified situations. In this case we simulated only the movement of the scatterers, and the obtained results are in agreement with some of the expected from the theory and qualitatively with the experimental results outlined in previous works. Also, we tested the first order statistics of the spatial speckle, the Briers contrast of the time varying part and the moment of inertia of the co-occurrence matrix.

Fractional order mean in image processing

We explore the features of a family of nonlinear filters called the fractional order mean. The median, the mode, and other statistical characteristics belong to this family as particular integer orders. The behavior of these filters in noise suppression in images is investigated. An improved version of these filters, which we call the 8-pixel window mean filter is also explored. In this case, the filtered value of the pixel is compared with its experimental value in the presence of a preset threshold. Noise suppression performance is tested with the usual mean square error (MSE) criterion, with a correlation criterion, and with a new criterion, the mean relative error (MRE). Evidence is found that the MRE correlates better than the MSE with the perceived visual quality of the processed image.

Speckle activity images based on the spatial variance of the phase

We propose the display of the local spatial variance of the temporal variations of the phase as an activity descriptor in dynamic speckle images. The spatial autocorrelation of the speckle intensity is calculated in sliding windows, and an estimation of the variance of the phase variations in each region of the sample is determined. The activity images obtained in this way depict some interesting features and in some cases they could be related to physical magnitudes in the samples. A simulation is presented, and examples corresponding to usual study cases are also shown, namely, fruit bruising and paint drying.

Decision and classification problems using Mahalanobis statistical distance

We present a method that uses Mahalanobis distance to study some decision and classification problems. Four examples are used to show the diversity of possible applications of our method. Based on two simulated sets of data, we have calculated the corresponding Mahalanobis distances and their sum and differences Holodiagrams. These diagrams are valuable visualization tools for studying decision and classification problems in the proposed applications.

Holodiagrams in birefringent media

The modifications to the holodiagram concept to describe free propagation (the extraordinary ray) inside birefringent materials are described. Holodiagrams are graphs showing the loci where the sum or the difference in the optical path from a generic point to two foci is the same. The holodiagrams obtained in this way give the shape of the surfaces that satisfy Fermats principle, conjugate by reflection of one focus into the other, and represent the interference fringes obtained if both points are coherent sources. The reflection law in birefringent media is investigated in relation to this diagram. One direction for the optical axis is considered: parallel to the line joining the source and the observation point. Quartz-type and calcite-type crystals are studied.

Refraction holodiagrams and Snell's law

Summary The refraction holodiagram RHD is analyzed here with respect to the law of refraction. Particularly, we study the surface that exactly conjugates by refraction a virtual point source with a real image or conversely. By using the total optical path as a parameter we build a diagram that consists in a family of Descartes ovals of the apple type that contains the Pascals limacon as a particular extreme case and the spherical surface with the Weierstrass points as another. These representations permit the straightforward application of Fermats principle in the case of arbitrary refracting surfaces and show the shape of generalized Fresnels zones in the intersections with any surface. Snells law is applied to rays incident on the apple type surfaces to find out the conditions for exact conjugation. Sensitivity to optical path variations is also discussed. The RHD curves family can be represented in a Cartesian way where the ovals appear as equally spaced straight lines.

Images of axial objects

Imaging of three-dimensional objects by lenses and mirrors is sometimes poorly indicated in textbooks and can be incorrectly drawn. We stress a need to clarify the concept of longitudinal magnification, with simulated images illustrating distortions introduced along the optical axis. We consider all possible positions of the object for both a convergent and a divergent lens, producing real and virtual images. We also discuss spherical mirrors, elementary telescopes and microscopes.