Texture Evaluation of Automotive Coatings by Means of a Gonio-Hyperspectral Imaging System Based on Light-Emitting Diodes

Sparkle and graininess are textural effects that appear as intrinsic spatial features of coatings containing goniochromatic pigments, whereas others such as mottling are undesired outcomes. In this study, we present new methods for the evaluation of sparkle, graininess and mottling of automotive coatings through images acquired with a novel gonio-hyperspectral imaging system based on light-emitting diodes with extended spectral sensitivity beyond the visible range (368–1309 nm). A novel analysis of sparkle that considered the amount of sparkling spots was used. Graininess was quantified through a novel statistical descriptor based on the energy descriptor computed from the histogram. A new index was proposed for an enhanced detection of mottling based on the analysis of striping, which was better observed and quantified in the infrared range. Spectral assessments showed a strong relationship with color and spectral reflectance for graininess and mottling. In conclusion, the results showed that these new spatial and spectral methods are a suitable, alternative and potential approach for the assessment of these textural features.Ministerio de Ciencia e Innovación (MICINN, DPI2011-30090-C02-01) and Ministerio de Economía y Competitividad (MINECO, DPI2014-56850-R); and the European Union

Depth, shading, and stylization in stereoscopic cinematography

Due to the constantly increasing focus of the entertainment industry on stereoscopic imaging, techniques and tools that enable precise control over the depth impression and help to overcome limitations of the current stereoscopic hardware are gaining in importance. In this dissertation, we address selected problems encountered during stereoscopic content production, with a particular focus on stereoscopic cinema. First, we consider abrupt changes of depth, such as those induced by cuts in films. We derive a model predicting the time the visual system needs to adapt to such changes and propose how to employ this model for film cut optimization. Second, we tackle the issue of discrepancies between the two views of a stereoscopic image due to view-dependent shading of glossy materials. The suggested solution eliminates discomfort caused by non-matching specular highlights while preserving the perception of gloss. Last, we deal with the problem of filmgrainmanagement in stereoscopic productions and propose a new method for film grain application that reconciles visual comfort with the idea of medium-scene separation.Aufgrund der ständig steigenden Beachtung der stereoskopische Abbildung durch die Unterhaltungsindustrie, gewinnen Techniken und Werkzeuge an Bedeutung, die eine präzise Steuerung der Tiefenwahrnehmung ermöglichen und Einschränkungen der gegenwärtigen stereoskopischen Geräte überwinden. In dieser Dissertation adressieren wir ausgewählte Probleme, die während der Erzeugung von stereoskopischen Inhalten auftreten, mit besonderem Schwerpunkt auf der stereoskopischen Kinematographie. Zuerst betrachten wir abrupte Tiefenänderungen, wie sie durch Filmschnitte hervergerufen werden. Wir leiten ein Modell her, das die Zeit vorhersagt, die für das menschliche Sehsystem notwendig ist, um sich an solche Änderungen der Tiefe zu adaptieren, und schlagen vor wie dieses Modell für Schnittoptimierung angewendet werden kann. Danach gehen wir das Problem der Unstimmigkeiten zwischen den zwei Ansichten eines stereoskopischen Bildes, infolge der sichtabhängigen Schattierung von glänzenden Materialien, an. Die vorgeschlagene Lösung eliminiert das visuelle Unbehagen, welches von nicht zusammenpassenden Glanzlichtern verursacht wird, indessen bewahrt sie die Glanzwahrnehmung. Zuletzt behandeln wir das Problem des Filmkornsmanagements in stereoskopischen Produktionen und schlagen eine neue Methode für das Hinzufügen vom Filmkorn vor, die die visuelle Behaglichkeit mit der Idee der Medium-Szenen-Trennung in Einklang bringt

Modelling the total appearance of gonio-apparent surfaces using stereo vision

Over recent decades, the textured coating provided by metallic surfaces has been an important factor in attracting customers of the automobile industry. This has meant that quantifying the appearance of coating products is essential for product development and quality control. The appearance of these coated products strongly depends on the viewing geometry, giving rise to a variety of properties of perceptual attributes such as texture, colour and gloss. Due to the visually-complex nature of such coatings, there remains an unsatisfied demand to develop techniques to measure the total appearance of metallic coatings. This study describes which aims to define the total appearance of metallic coatings and then objectively characterise it. Total appearance here refers to the combination of three properties of perceptual attributes of the surface: glint, coarseness and brightness. A number of metallic panels were visually scaled and a computational model capable for predicting three perceptual attributes was developed. A computational model was developed to relate the results from this psychophysical experiment to data obtained from a stereo image capture system. This is a new alternative technique aimed at solving one of the most challenging problems in computer vision: stereo matching. In the system, two images are captured by a same camera under two different lighting conditions to mimic stereoscopic vision. This not only addresses the problem of stereo matching (i.e. to find the corresponding pixels between two images) but also enhances the effect of perceptual attributes. After linearisation of camera response, spatial uniformity correction was performed to minimise the effect of uneven illumination. A characterisation method was then used to transfer the RGB to device-independent values. Two images captured under different lighting conditions were merged to obtain stereo data. In glint feature extraction, the pixels in the final image were segmented into two regions: bright spots and dark background. Next, statistical analyses were applied to extract features. Finally a model was created to predict the glint attribute of the metallic coating panels based on an image captured by the stereo capture system. In coarseness feature extraction, the merged image transformed to frequency domain using a discrete Fourier Transform. An octave bandpass filter was then applied to the Fourier Spectra image and data analysis was carried out to achieve the “image variance value” for each band. In similar to final step of glint, a model was created to predict the coarseness attribute

Modelling texture appearance of gonioapparent objects

Quantifying the appearance of coating products is essential in the automobile and automobile finishing industries for efficient product development and product/quality control. There is a specific need to develop techniques to measure the total appearance of metallic coatings. The present study focuses on two key attributes of visual texture: coarseness and glint. In order to develop models to capable of measuring these attributes, it was first necessary to design psychophysical experiments for assessing coarseness and glint as perceived on metallic-coating panels. The change in the appearance of the metallic coatings is known as a gonioapparent effect, and is greatly dependant on the illumination and viewing conditions. Therefore, appropriate conditions were carefully examined for the independent observation of coarseness and glint in order to discern those attributes. It was found that diffuse illumination was appropriate for viewing coarseness and directional illumination was appropriate for observing glint. Under these appropriately-controlled conditions, the perceptual coarseness and glint of sets of metallic-coating panels were assessed by human observers. A digital camera was used to capture information on the spatial detail of the metallic-coating panels. An image of each panel was captured under the same viewing conditions as used for the visual assessments. The information in a single image was sufficient to represent a metallic-coating panel under identical diffuse illumination conditions for which observers assessed coarseness. For capturing information on glint, however, a high dynamic-range (HDR) image was necessary because the dynamic range of the scene in which the glint was observed exceeded that of the camera used in this study. Two computational models were developed to predict perceptual coarseness and perceptual glint by extracting associated features from the captured images. The performance of these models was verified by comparing predictions made using them with the perceptual coarseness and glint scaled by observers. For industrial use, the visualisation of products on computer displays would give various opportunities, for example, to develop and design products or coatings and also to communicate appearance information. A digital camera and a suitable display would enable this to be achieved, but the ability to reproduce the appearance of metallic-coating products on displays in a satisfactory manner was found to have significant ~ challenges. The coarseness model developed in the present study was able to represent perceptual coarseness based on the images captured by the digital camera. However, the resolution of the images was not high enough to resolve the individual aluminium flakes contained in the coatings, which contribute to the visual texture. Therefore, verification of the images was carried out for the coarseness attribute by comparing the coarseness perceived in the images displayed on a liquid-crystal display (LCD) with the metallic-coating panels themselves. In addition to camera limitations, LCD resolution also prevented the same conditions used for physical panel assessment from being replicated. Therefore, two optimal conditions were selected and perceptual coarseness was scaled using images. Besides the difference in experimental conditions, there was also a difference in the "absolute" texture appearance between the two media because of errors in image reproduction of the images. In spite of this, the relatively-scaled perceptual coarseness for the image samples agreed well with that for the original physical samples. This implies that it is practicable to assess perceptual coarseness from an image on a display that simulates a metallic-coating pane