This paper presents a comparison of color spaces for material classification. The study includes three device-independent (CIELAB, CIELUV, and CIE XYZ) and seven device-dependent spaces (RGB, HSV, YIQ, YUV, YCbCr, Ohta’s I1I2I3, and RG-YeB-WhBl). The pros and cons of the different spaces and the procedures for converting color data among them are discussed in detail. An experiment based on 12 different image data sets was carried out to comparatively evaluate the performance of each space for material classification purposes. The results showed that CIELAB markedly outperformed the other spaces followed by HSV and CIELUV. Conversely, CIE XYZ came out as the worst performing space. Interestingly, no significant difference emerged among the performance of the other device-dependent spaces.
We present a set of multiscale, multidirectional, rotation-invariant features for color texture characterization. The proposed model is based on the ranklet transform, a technique relying on the calculation of the relative rank of the intensity level of neighboring pixels. Color and texture are merged into a compact descriptor by computing the ranklet transform of each color channel separately and of couples of color channels jointly. Robustness against rotation is based on the use of circularly symmetric neighborhoods together with the discrete Fourier transform. Experimental results demonstrate that the approach shows good robustness and accuracy.
A novel approach to surface contouring using two-source phase-stepping digital shearography is proposed. In this technique, the illumination source is displaced in a prescribed manner to produce a phase difference increment. For a particular experimental arrangement, this phase change is a function of the height coordinates of two sheared points of the object. Therefore, if the height of the sheared point is known, the phase change in each pixel only depends on the height in the same pixel. This requitement is fulfilled by placing a reference plan of suitable dimensions inside the field of view. To measure the shape of a 3D object, first we calculate the phase change using the well- known five-bucket algorithm of phase stepping, and then we use iteration and interpolation routines to find a height value, for which the difference between the phase change calculated by phase stepping and the theoretical value obtained for this height is smaller than a given tolerance. Results obtained with computer-generated shearing speckle interferograms are significantly more accurate than if a linear relationship between phase change and 3D shape is assumed. Finally, we discuss the performance of the suggested approach.
We report on a novel technique for the evaluation of transient phase in double-pulsed electronic speckle-shearing pattern interferometry. Our technique requires the acquisition of just two speckle-shear interferograms which are correlated by subtraction to obtain a fringe pattern. A spatial carrier is generated by means of an original optical setup based on the separation and later recombination of the two beams produced by a Nd:YAG twin pulsed laser. One introduces an optical path difference in the curvature radii of the illumination beams by mismatching the distances from two diverging lenses to a beam combiner. This procedure gives rise to a linear phase term in the second speckle- shear interferogram that plays the role of a spatial carrier and allows the use of spatial phase measurement methods to analyze the fringe pattern. We present the theoretical aspects of the technique as well as its experimental implementation.
We present a novel technique for the application of stroboscopic additive TV-holography to the measurement of vibrations using temporal phase-shifting. Based on a previous concept - contrived and developed by the same authors - that used two illumination pulses within each vibration cycle and interpulse phase modulation at the same rate that the vibration of the object, this new technique implements and analogous phase modulation scheme but between two swiftly alternating bursts of single pulses with different phase within each video frame, rather than using true double-pulses, thus allowing quantitative measurements to be performed with stroboscopic illumination keeping the characteristics of stability and temporal resolution of the double-pulse additive stroboscopic technique but with the additional benefit of reaching high vibration frequencies with low bandwidth phase modulators.
In this paper we demonstrate the feasibility of impact- induced transient deformations measurement by single-pulsed subtraction TV holography an the Fourier transform method with contouring fringes as spatial carrier. Fringe formation in single-pulsed subtraction TV holography and phase demodulation by the Fourier transform method are descried. Contouring fringes are proved to be well suited for introducing spatial carrier in the correlation fringe patterns. Experimental results are presented. Finally, the degree of immunity to environmental disturbances of this technique is discussed and improvements are proposed.
We have previously proposed a phase evaluation method of multiple-beam Fizeau patterns that combines the two-beam phase-stepping algorithms with the more effect. This method is based on a multiplicative moire image formation process obtained y the direct superposition of high-frequency multiple-beam Fizeau carrier fringes on a transmission grating. In this paper the contrast between this Moire two- beam phase-stepping technique and the direct evaluation of the high-frequency multiple-beam Fizeau carrier fringes by means of the Fourier Transform Method is presented.
The topographic measurement of high reflectivity test surfaces in a Fizeau interferometer using different two-beam phase-stepping algorithms (TBPSA's) is presented. Low pass- filtering the superposition of a multiple-beam Fizeau pattern and a Ronchi grid renders a pattern of sinusoidal profile (the moire image) that contains the Fizeau phase and that can be phase modulated by the in-plane translation of the grid. A set of these phase-shifted moire images can be combined in different TBPSA's in order to calculate the Fizeau phase making clear, at the same time, the sensitivity of the method to use the main phase error sources.
Two TV-holographic techniques to detect cracks in mechanical elements are demonstrated. One of them employs continuous illumination and is based in the modal analysis of the part. The other one consists in the study by pulsed TV-holography of transient waves induced in the part.
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