We evaluate three link functions (square root, logit, and copula) and Matérn kernel in the kernel-based estimation of reflectance spectra of the Munsell Matte collection in the 400-700 nm region. We estimate reflectance spectra from RGB camera responses in case of real and simulated responses and show that a combination of link function and a kernel regression model with a Matérn kernel decreases spectral errors when compared to a Gaussian mixture model or kernel regression with the Gaussian kernel. Matérn kernel produces performance similar to the thin plate spline model, but does not require a parametric polynomial part in the model.

Hyperspectral imaging provides more information than conventional RGB images. However, its high dimensionality prevents its adaptation to the existing image processing techniques. Defining full-band spectral feature is the first missing step, which is currently dealt with indirectly by band selection or dimension reduction. This article proposes a spectral feature extraction method using the mathematical moments to quantify the shape of the reflectance spectrum from different aspects. A whole family of features is presented by changing the moment attributes. All the features and their combinations are extensively tested in texture analysis of a new hyperspectral image database from textile samples (SpecTex). Two supervised experiments are performed: image patch classification and pixel-wise mosaic image segmentation. The proposed features are compared to four other features: the grayscale intensity, the RGB and CIELab values, and the principal components. Also, three analysis methods are tested: co-occurrence matrix, Gabor filter bank, and local binary pattern. In all cases, the moment features outperformed the opponents. Notably, combining the moment features with complementary attributes remarkably improved the performance. The most discriminative combinations are studied and formulated in this article. Keywords Feature extraction • Moments • Hyperspectral imaging • Texture analysis • Image database • This study was funded by the Finnish Funding Agency for Innovation (TEKES), funding decision 3268/31/2015.

The aim of this work is automatic and efficient detection of medically-relevant features from oral and dental hyperspectral images by applying up-to-date deep learning convolutional neural network techniques. This will help dentists to identify and classify unhealthy areas automatically and to prevent the progression of diseases. Hyperspectral imaging approach allows one to do so without exposing the patient to ionizing X-ray radiation. Spectral imaging provides information in the visible and near-infrared wavelength ranges. The dataset used in this paper contains 116 hyperspectral images from 18 patients taken from different viewing angles. Image annotation (ground truth) includes 38 classes in six different sub-groups assessed by dental experts. Mask region-based convolutional neural network (Mask R-CNN) is used as a deep learning model, for instance segmentation of areas. Preliminary results show high potential and accuracy for classification and segmentation of different classes.

Wind-up, a condition related to chronic pain, is described traditionally as a frequency dependent increase in the excitability of sensory spinal cord neurons, evoked by electrical stimulation of small pain fibers. In this paper, we introduce a computational model on wind-up of large (Abeta) fibers, considering three major mechanisms of wind-up: 1) a feedforward mechanism causing Ca2+ entry, 2) a positive feedback, causing more Ca2+ entry, and 3) a feedforward due to sprouting of Abeta fibers towards the small pain fibers. Our model proposes three different ways for reducing wind-up and shows the most important way to treat the pain.

At the cost of added complexity and time, hyperspectral imaging provides a more accurate measure of the scene’s irradiance compared to an RGB camera. Several camera designs with more than three channels have been proposed to improve the accuracy. The accuracy is often evaluated based on the estimation quality of the spectral data. Currently, such evaluations are carried out with either simulated data or color charts to relax the spatial registration requirement between the images. To overcome this limitation, this article presents an accurately registered image database of six icon paintings captured with five cameras with different number of channels, ranging from three (RGB) to more than a hundred (hyperspectral camera). Icons are challenging topics because they have complex surfaces that reflect light specularly with a high dynamic range. Two contributions are proposed to tackle this challenge. First, an imaging configuration is carefully arranged to control the specular reflection, confine the dynamic range, and provide a consistent signal-to-noise ratio for all the camera channels. Second, a multi-camera, feature-based registration method is proposed with an iterative outlier removal phase that improves the convergence and the accuracy of the process. The method was tested against three other approaches with different features or registration models.