In the recent years, many objective image quality assessment methods have been proposed by different researchers, leading to a significant increase in their correlation with subjective quality evaluations. Although many recently proposed image quality assessment methods, particularly full-reference metrics, are in some cases highly correlated with the perception of individual distortions, there is still a need for their verification and adjustment for the case when images are affected by multiple distortions. Since one of the possible approaches is the application of combined metrics, their analysis and optimization are discussed in this paper. Two approaches to metrics’ combination have been analyzed that are based on the weighted product and the proposed weighted sum with additional exponential weights. The validation of the proposed approach, carried out using four currently available image datasets, containing multiply distorted images together with the gathered subjective quality scores, indicates a meaningful increase of correlations of the optimized combined metrics with subjective opinions for all datasets.

Quality assessment of the 3D printed surfaces is one of the crucial issues related to fast prototyping and manufacturing of individual parts and objects using the fused deposition modeling, especially in small series production. As some corrections of minor defects may be conducted during the printing process or just after the manufacturing, an automatic quality assessment of object’s surfaces is highly demanded, preferably well correlated with subjective quality perception, considering aesthetic aspects. On the other hand, the presence of some greater and more dense distortions may indicate a reduced mechanical strength. In such cases, the manufacturing process should be interrupted to save time, energy, and the filament. This paper focuses on the possibility of using some general-purpose full-reference image quality assessment methods for the quality assessment of the 3D printed surfaces. As the direct application of an individual (elementary) metric does not provide high correlation with the subjective perception of surface quality, some modifications of similarity-based methods have been proposed utilizing the calculation of the average mutual similarity, making it possible to use full-reference metrics without the perfect quality reference images, as well as the combination of individual metrics, leading to a significant increase of correlation with subjective scores calculated for a specially prepared dataset.

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In the paper an algorithm for binarization of grayscale images representing text documents together with its optimization is presented. In the proposed approach two classical global thresholding algorithms proposed by Otsu and Kapur are combined with their local versions applied for blocks. The experimental results have been obtained for the H-DIBCO test dataset containing handwritten text images together with their "groundtruth" binary equivalents. Streszczenie. W artykule zaprezentowano algorytm binaryzacji obrazów w skali szarości przedstawiających dokumenty tekstowe wraz z jego optymalizacją. Przedstawione podejście bazuje na połączeniu dwóch klasycznych metod progowania zaproponowanych przez Otsu i Kapura z ich lokalnymi wariantami zastosowanymi dla bloków. Wyniki eksperymentalne uzyskano dla bazy testowej H-DIBCO zawierającej obrazy rękopisów wraz z ich binarnymi odpowiednikami stanowiącymi wzorce. Binaryzacja obrazów dokumentów z użyciem zmodyfikowanych lokalno-globalnych algorytmów Otsu i Kapura