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Color technology needs specifications to which extent physical differences of stimuli correspond to differences in perception. Generalized linear models (GLMs) have proved successful to provide such specifications from choice-based experiments. However, the use of GLMs imposes practical restrictions on the experiment and stimulus parameters. We propose an alternative analytic approach based on machine learning and demonstrate its use in designing and analyzing choice-based experiments with multiple stimulus dimensions. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 334-343, 2013 [ABSTRACT FROM AUTHOR]

We show that conjoint analysis, a popular multi-attribute preference assessment technique used in market research, is a well suited tool to evaluate a multitude of gamut mapping algorithms simultaneously. Our analysis is based on data from psychovisual tests assessed in a laboratory and in a web environment. Conjoint analysis allows us to quantify the contribution of every single parameter value to the perceived value of the algorithm; it also allows us to test the influence of additional parameters like gamut size or color shifts.We show that conjoint analysis can be individualized to images or observers if enough data is available. Especially promising in this respect is the combination of individual and population data. [ABSTRACT FROM AUTHOR]

Our topic is the potential of combining global gamut mapping with spatial methods to retain the percepted local image information in gamut mapping algorithms. The main goal is to recover the original local contrast between neighboring pixels in addition to the usual optimization of preserving lightness, saturation, and global contrast. Special emphasis is placed on avoiding artifacts introduced by the gamut mapping algorithm itself. We present an unsharp masking technique based on an edge-preserving smoothing algorithm allowing to avoid halo artifacts. The good performance of the presented approach is verified by a psycho-visual experiment using newspaper printing as a representative of a small destination gamut application. Furthermore, the improved mapping properties are documented with local mapping histograms. [ABSTRACT FROM AUTHOR]

We present a real-time THz imaging method using a commercial fiber-coupled photo conductive antenna as the THz source and an uncooled microbolometer camera for detection. This new combination of state-of-the-art components is very adaptable due to its compact and uncooled radiation source, whose fiber coupling allows for a flexible placement. Using a camera with high sensitivity renders real-time imaging possible. As a proof-of-concept, the beam shape of a THz Time Domain Spectrometer was measured. We demonstrate real time imaging at nine frames per second and show its potential for practical applications in transmission geometry covering both material science and security tasks. The results suggest that hidden items, complex structures and the moisture content of (biological) materials can be resolved. We discuss the limits of the current setup, possible improvements and potential (industrial) applications, and we outline the feasibility of imaging in reflection geometry or extending it to multi-spectral imaging using band pass filters. [ABSTRACT FROM AUTHOR]

• Single sided air coupled ultrasonic inspection setup with Lamb waves. • Defect detection and localization by Lamb mode conversion. • Signal analysis for dispersive Lamb waves. • Separation of overlapping Lamb modes and estimation of the dispersion relation. In this paper we demonstrate a non-destructive, non-contact detection method for small defects in thin polymer plates using an air coupled ultrasonic (ACUS) setup. There exist many applications for such methods, e.g. quality control in the manufacturing process or failure prevention by periodical inspections during the lifetime of a product. We demonstrate a setup for the inspection of plates together with signal analysis algorithms to process the measured data, meeting the challenges to handle the dispersive signals and establishing a robust failure criterion. Pressure waves from the transmitter excite different modes of Lamb waves inside the plate. These Lamb waves propagate in the plate and reradiate pressure waves into the air that are then detected by the receiver. Lamb mode conversion is used for defect detection. A numerical model allows the visualization of the propagating waves in the air as well as the Lamb waves inside the plate. Four key parameters of the setup are identified, two angles and two distances. The transmitter and the receiver angles are used to select which Lamb mode (anti-symmetric A 0 or symmetric S 0) is mainly excited and detected, respectively. For the acquisition of the Lamb wave signal the distance from the transmitter to the receiver should be as large as possible but is limited by the attenuation of the signal. Measurements for different values of this distance are essential for signal analysis. The distance between transducer and plate surface should be as small as possible even if it may introduce secondary Lamb waves due to reflections of the pressure wave between transmitter and plate surface. Two algorithms, a model based one and a data driven one, are presented to separate Lamb modes that overlap in time. In these separated signals, the Lamb mode conversion from A 0 to S 0 is shown, allowing a localization of the defect. We conclude that defect detection and localization with Lamb mode conversion is possible with an air coupled ultrasonic setup. Multiple measurements along the propagation direction of the Lamb waves are necessary to allow a thorough signal analysis and visualize the mode conversion. [ABSTRACT FROM AUTHOR]

Zusammenfassung Bildgebung mit Terahertzstrahlung basiert bislang auf Abscannen eines Objekts mit einem Detektor. Mikrobolometer‐Kameras ermöglichen nun eine Bildgebung wie bei einer normalen Kameratechnik. Das erlaubt auch den Einsatz holografischer Methoden. Bei ausreichend Platz, um einen Referenzstrahl seitlich in die Kamera einzustrahlen, ist herkömmliche digitale Holografie möglich. Ist es dafür zu eng, lässt sich über die Methode der Ptychografie holografische Information gewinnen. Trotz der großen THz‐Wellenlänge reicht die dreidimensionale Ortsauflösung für Anwendungen in der Biomechanik. So lässt sich die Kontaktfläche einer Fingerkuppe mit dem Untergrund genau untersuchen. Bildgebung mit Terahertzstrahlung basiert bislang auf Abscannen eines Objekts mit einem Detektor. Mikrobolometer‐Kameras ermöglichen nun eine Bildgebung wie mit jeder Kameratechnik. Flächendetektoren erlauben überdies den Einsatz holografischer Methoden. Trotz der großen Wellenlänge reicht die dreidimensionale Ortsauflösung für Anwendungen in der Biomechanik. [ABSTRACT FROM AUTHOR]

Air-coupled ultrasound (ACU) is increasingly used for nondestructive testing (NDT). With ACU, no contact or coupling agent (e.g., water and ultrasound gel) is needed between transducers and test sample, which provides high measurement reproducibility. However, for testing in production, a minimum separation is often necessary between the sample and the transducers to avoid contamination or transducer damage. Due to wave diffraction, the collimation of the ultrasound beam decreases for larger propagation distances, and ACU images become blurred and show lower defect lateral resolution with increasing sample–transducer separation. This is especially critical to thick composites, where large-size planar sources are used to bridge the large ACU transmission loss with good collimation. In this work, ACU reradiation in unbounded media is extended to NDT of multilayered composites. The extended method is named ACU time reversal (ACU-TR) and significantly improves the defect resolution of ACU imaging. With ACU-TR, the complete pressure distribution radiated by large ACU source is measured with point receivers (RXs) in one plane arbitrarily separated from the sample. By applying acoustic holography physics, it is then possible to quantitatively reconstruct the pressure field directly at arbitrary sample defect planes, which compensates for undesired diffraction phenomena and improves minimum detectable defect size, thereby achieving subwavelength lateral resolution. We tested the method on complex wood-based composite samples based on the ACU far-field measurements at a separation of 160 mm between the sample and the RX transducer. With the proposed method, it is possible to detect surface defects as well as inner defects within composite boards. In the future, by using point RX arrays instead of a scanned microphone, both data acquisition and evaluation can be potentially implemented in real time. [ABSTRACT FROM AUTHOR]

Abstract Ultrasonic, non-contact defect detection for polymer pipes can provide an easy and reliable method to establish on site quality control without destructive mechanical testing and finally may help to prevent damage from leaking pipes. The target is to inspect thin walled polymer pipes made of PVDF and PP with small defects in the pipe wall. Air coupled transducers with a nominal frequency of 200 kHz are used to excite Lamb waves in the pipe wall that interact with potential defects. A reference measurement on a flawless part of the pipe helps to mitigate the effects of geometrical and material inhomogeneities. The possibility to excite only the A 0 Lamb wave mode in thin plates and pipes using air coupled transducers is shown. Defects attenuate the propagating Lamb waves, resulting in a characteristic pattern in the receiver signal. Simulations on the Lamb wave propagation help to identify the dispersion parameters and allow to understand the effect of defects better. The detection of defects is challenging because of other imperfections in the specimen. With a reference measurement the detection of defects down to a size of 1 mm is possible. [ABSTRACT FROM AUTHOR]

In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8--14 µm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 µm, 118.8 µm, and 393.6 µm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed. [ABSTRACT FROM AUTHOR]

Existing image-difference measures show excellent accuracy in predicting distortions, such as lossy compression, noise, and blur. Their performance on certain other distortions could be improved; one example of this is gamut mapping. This is partly because they either do not interpret chromatic information correctly or they ignore it entirely. We present an image-difference framework that comprises image normalization, feature extraction, and feature combination. Based on this framework, we create image-difference measures by selecting specific implementations for each of the steps. Particular emphasis is placed on using color information to improve the assessment of gamut-mapped images. Our best image-difference measure shows significantly higher prediction accuracy on a gamut-mapping dataset than all other evaluated measures. [ABSTRACT FROM AUTHOR]

We explore the potential of image-dependent gamut mapping as a constrained optimization problem. The performance of our new approach is compared to standard reference gamut mapping algorithms in psycho-visual tests. [ABSTRACT FROM AUTHOR]