Dithered Color Quantization

Image quantization and digital halftoning are fundamental problems in computer graphics, which arise when displaying high-color images on non-truecolor devices. Both steps are generally performed sequentially and, in most cases, independent of each other. Color quantization with a pixel-wise defined distortion measure and the dithering process with its local neighborhood optimize different quality criteria or, frequently, follow a heuristic without reference to any quality measure. In this paper we propose a new method to simultaneously quantize and dither color images. The method is based on a rigorous cost–function approach which optimizes a quality criterion derived from a generic model of human perception. A highly efficient algorithm for optimization based on a multiscale method is developed for the dithered color quantization cost function. The quality criterion and the optimization algorithms are evaluated on a representative set of artificial and real–world images as well as on a collection of icons. A significant image quality improvement is observed compared to standard color reduction approaches

Quantitative assessment of pain-related thermal dysfunction through clinical digital infrared thermal imaging

BACKGROUND: The skin temperature distribution of a healthy human body exhibits a contralateral symmetry. Some nociceptive and most neuropathic pain pathologies are associated with an alteration of the thermal distribution of the human body. Since the dissipation of heat through the skin occurs for the most part in the form of infrared radiation, infrared thermography is the method of choice to study the physiology of thermoregulation and the thermal dysfunction associated with pain. Assessing thermograms is a complex and subjective task that can be greatly facilitated by computerised techniques. METHODS: This paper presents techniques for automated computerised assessment of thermal images of pain, in order to facilitate the physician's decision making. First, the thermal images are pre-processed to reduce the noise introduced during the initial acquisition and to extract the irrelevant background. Then, potential regions of interest are identified using fixed dermatomal subdivisions of the body, isothermal analysis and segmentation techniques. Finally, we assess the degree of asymmetry between contralateral regions of interest using statistical computations and distance measures between comparable regions. RESULTS: The wavelet domain-based Poisson noise removal techniques compared favourably against Wiener and other wavelet-based denoising methods, when qualitative criteria were used. It was shown to improve slightly the subsequent analysis. The automated background removal technique based on thresholding and morphological operations was successful for both noisy and denoised images with a correct removal rate of 85% of the images in the database. The automation of the regions of interest (ROIs) delimitation process was achieved successfully for images with a good contralateral symmetry. Isothermal division complemented well the fixed ROIs division based on dermatomes, giving a more accurate map of potentially abnormal regions. The measure of distance between histograms of comparable ROIs allowed us to increase the sensitivity and specificity rate for the classification of 24 images of pain patients when compared to common statistical comparisons. CONCLUSIONS: We developed a complete set of automated techniques for the computerised assessment of thermal images to assess pain-related thermal dysfunction

Hyperfeatures - multilevel local coding for visual recognition

International audienceHistograms of local appearance descriptors are a popular representation for visual recognition. They are highly discriminant and have good resistance to local occlusions and to geometric and photometric variations, but they are not able to exploit spatial co-occurrence statistics at scales larger than their local input patches. We present a new multilevel visual representation, ‘hyperfeatures', that is designed to remedy this. The starting point is the familiar notion that to detect object parts, in practice it often suffices to detect co-occurrences of more local object fragments – a process that can be formalized as comparison (e.g. vector quantization) of image patches against a codebook of known fragments, followed by local aggregation of the resulting codebook membership vectors to detect co-occurrences. This process converts local collections of image descriptor vectors into somewhat less local histogram vectors – higher-level but spatially coarser descriptors. We observe that as the output is again a local descriptor vector, the process can be iterated, and that doing so captures and codes ever larger assemblies of object parts and increasingly abstract or ‘semantic' image properties. We formulate the hyperfeatures model and study its performance under several different image coding methods including clustering based Vector Quantization, Gaussian Mixtures, and combinations of these with Latent Dirichlet Allocation. We find that the resulting high-level features provide improved performance in several object image and texture image classification tasks

(Guest Editors) Dithered Color Quantization

Image quantization and digital halftoning are fundamental problems in computer graphics, which arise when displaying high-color images on non-truecolor devices. Both steps are generally performed sequentially and, in most cases, independent of each other. Color quantization with a pixel-wise defined distortion measure and the dithering process with its local neighborhood optimize different quality criteria or, frequently, follow a heuristic without reference to any quality measure. In this paper we propose a new method to simultaneously quantize and dither color images. The method is based on a rigorous cost–function approach which optimizes a quality criterion derived from a generic model of human perception. A highly efficient algorithm for optimization based on a multiscale method is developed for the dithered color quantization cost function. The quality criterion and the optimization algorithms are evaluated on a representative set of artificial and real–world images as well as on a collection of icons. A significant image quality improvement is observed compared to standard color reduction approaches. 1

WAYflow - Mobilitaet in Ballungsraeumen Gesamtsachbericht

Available from TIB Hannover: F04B1891 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman

EUF-Testleistungen wehrpflichtiger junger Maenner im wiedervereinigten Deutschland Regionale Unterschiede bei Intelligenzleistungen und den Basisfertigkeiten Rechnen und Rechtschreibung

'Leistungsbilder der Wehrpflichtigen aus den verschiedenen Bundeslaendern, die in den Jahren 1992 bis 1998 beim Psychologischen Dienst der Bundeswehr die Eignungsuntersuchung und Eignungsfeststellung (EUF) durchlaufen haben, zeigen gewichtige regionale Unterschiede. Ein auffaelliges West-Ost-Leistungsgefaelle, das noch in den ersten Jahren nach der Wiedervereinigung zu beobachten war, hat sich zwischenzeitlich deutlich verringert. Wie eine vergleichende Betrachtung der verschiedenen Bundeslaender zeigt, ist es in den letzten Jahren von einem stabilen, in Ost und West gleichermassen zu beobachtenden Sued-Nord-Gefaelle ueberlagert worden. Da die suedlichen Laender vor allem durch eine starke Wirtschaftskraft gekennzeichnet sind, wird postuliert, dass wirtschaftliche Prosperitaet die foerderlichen Rahmenbedingungen schafft, in denen sich die Leistungspotentiale junger Menschen entfalten und die mehr als andere Einflussgroessen regionale Unterschiede im Leistungsverhalten erklaeren koennen.' (Autorenreferat)'The conscripts from different Lands of the Federal Republic of Germany who had passed through the qualifying examinations and aptitude tests at the Bundeswehr Psychological Service between 1992 and 1998 showed achievements with considerable differences from region to region. The remarkable East-West slope that could be observed during the early years after Germany's reunification meanwhile has been significantly reducing. A comparative study of the different Lands shows that this slope now is being overlaid by a steady South-North slope to be observed in the East and in the West as well. Since the southern Lands are being particularly characterised by their strong economy, it is postulated that economic prosperity creates those encouraging frame conditions where the youth have the full scope for developing their potential of achievement. Thus, more than any other factors of influence, economic prosperity may explain the regional differences of achievements.' (author's abstract)SIGLEAvailable from UuStB Koeln(38)-2000106106 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman