Near-infrared hyperspectral imaging is becoming a popular tool in various fields. In all imaging systems, proper illumination is crucial for attaining optimal image quality that is needed for the best performance of image analysis algorithms. In hyperspectral imaging, the acquired spectral signature has to be representative in all parts of the imaged object. Therefore, the whole object must be equally well illuminated–without shadows or specular reflections. As there are no restrictions imposed on the material and geometry of the object, the desired illumination of the object can only be achieved with completely diffuse illumination. In order to minimize shadows and specular reflections, the light illuminating the object must be spatially, angularly and spectrally uniform. The quality of illumination systems for hyperspectral imaging can therefore be assessed using spatial-intensity, spatial-spectral, angular-intensity and angular-spectral non-uniformity measures that are presented in this paper. Emphasis is given to the angular-intensity and angular-spectral non-uniformity measures, which are the most important contributions of this paper. The measures were defined on images of two reference targets—a flat, white diffuse reflectance target and a sphere grid target—acquired with an acousto-optic tunable filter (AOTF) based hyperspectral imaging system. The proposed measures were tested on a ring light and on a diffuse dome illumination system.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 9764692The accuracy of the radiometric response of acousto-optic tunable filter (AOTF) hyperspectral imaging systems is crucial for obtaining reliable measurements. It is therefore important to know the adiometric response and noise characteristics of the hyperspectral imaging system used. A radiometric model of an AOTF hyperspectral imaging system composed of an imaging sensor radiometric model (CCD, CMOS, and sCMOS) and an AOTF light transmission model is proposed. Using the radiometric model, a method for obtaining the fixed pattern noise (FPN) of the imaging system by displacing and imaging an illuminated reference target is developed. Methods for estimating the temporal noise of the imaging system, using the photon transfer method, and for correcting FPN are also presented. Noise estimation and image restoration methods were tested on an AOTF hyperspectral imaging system. The results indicate that the developed methods can accurately calculate temporal and FPN, and can effectively correct the acquired images. After correction, the signal-to-noise ratio of the acquired images was shown to increase by 26%.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 9842516We have constructed an industrial prototype imaging system for real-time in-process measurement of the most prominent pellet properties, such as the size and shape of pellets and the coating thickness and uniformity, that effectively combines the novel methods for calibration and enhancement of hyperspetral images and the novel robust fully automated methods for real-time analysis of the enhanced images. Results of the extensive evaluation based on multiple coating processes showed that the prototype imaging system and the novel image processing methods developed during the project produce accurate measurements that match the results obtained by established off-line laboratory reference methods. The prototype system will provide a solid foundation for construction of innovative complex measurement systems and instruments, providing the means for efficiently designing, optimizing and controlling the production of pharmaceutical pellets and assessing the quality of pellets according to the PAT initiative. Development of such modern high-tech system with high value added, is essential for boosting the the economic growth, and generating new well-paid jobs.
F.08 Development and manufacture of a prototype
COBISS.SI-ID: 3650417