Publicēti raksti (ASI) / Published Articles

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Browsing Publicēti raksti (ASI) / Published Articles by Author "Likar, Boštjan"

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    Color constancy in dermatoscopy with smartphone
    (SPIE, 2017-12-07) Cugmas, Blaž; Pernuš, Franjo; Likar, Boštjan
    The recent spread of cheap dermatoscopes for smartphones can empower patients to acquire images of skin lesions on their own and send them to dermatologists. Since images are acquired by different smartphone cameras under unique illumination conditions, the variability in colors is expected. Therefore, the mobile dermatoscopic systems should be calibrated in order to ensure the color constancy in skin images. In this study, we have tested a dermatoscope DermLite DL1 basic, attached to Samsung Galaxy S4 smartphone. Under the controlled conditions, jpeg images of standard color patches were acquired and a model between an unknown device-dependent RGB and a device independent Lab color space has been built. Results showed that median and the best color error was 7.77 and 3.94, respectively. Results are in the range of a human eye detection capability (color error ≈ 4) and video and printing industry standards (color error is expected to be between 5 and 6). It can be concluded that a calibrated smartphone dermatoscope can provide sufficient color constancy and can serve as an interesting opportunity to bring dermatologists closer to the patients.
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    Poor optical stability of molecular dyes when used as absorbers in water-based tissue-simulating phantoms
    (SPIE, 2019-02-27) Cugmas, Blaž; Naglič, Peter; Menachery, Sunil Paul Matthew; Pernuš, Franjo; Likar, Boštjan
    Biomedical optical systems and models can be easily validated by the use of tissue-simulating phantoms. They can consist of water-based turbid media which often include inks (India ink and molecular dyes) as absorbers. Optical stability of commonly exploited inks under the influence of light, pH changes and the addition of TiO2 and surfactant, was studied. We found that the exposure to ultraviolet and visible light can crucially affect the absorption properties of molecular dyes. On average, absorption peaks decreased by 47.3% in 150 exposure hours. Furthermore, dilution can affect ink’s pH and by that, its decay rate under light exposure. When TiO2 was added to the phantoms, all molecular dyes decayed rapidly. Photocatalytic nature of TiO2 can be partially avoided by selecting TiO2 with surface and crystal structure modification. Surfactant, normally present in the phantoms with polystyrene spheres, can cause absorption peak shifts up to 20 nm and amplitude changes of 29.6%. Therefore, it is crucial to test the optical stability of inks in the presented manner before their exploitation in water-based phantoms.