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UV Reflectance Photography
Published in Adrian Davies, Digital Ultraviolet and Infrared Photography, 2017
Special targets are designed specifically for the purpose. One example is Spectralon, a fluoropolymer, which has the highest diffuse reflectance of any known material or coating, across the UV, visible and near IR regions of the spectrum, It exhibits Lambertian behaviour (i.e. the apparent brightness of the surface to an observer is the same regardless of the observer’s angle of view). These targets are expensive, however, and may be in excess of what is required. A good alternative is PTFE (polytetrafluoroethylene, a Teflon plastic polymer) available in white or grey surfaces. I bought a roll of grey 2cm wide PTFE tape, and wrapped it several times around a 5cm square white tile to ensure that it was a solid grey tone. PTFE does have excellent Lambertian characteristics.
Hyperspectral Imaging of Diabetes Mellitus Skin Complications
Published in Andrey V. Dunaev, Valery V. Tuchin, Biomedical Photonics for Diabetes Research, 2023
Viktor V. Dremin, Evgenii A. Zherebtsov, Alexey P. Popov, Igor V. Meglinski, Alexander V. Bykov
A broadband illumination unit utilizing 50W halogen lamp was constructed, based on a fiber-optic ring illuminator (Edmund Optics, USA), providing a uniform distribution of light intensity in the camera focal plane with the average irradiance of 4.3 ± 0.5 mW/cm2 in the camera field of view (FOV) on the skin surface. The use of the ring illuminator made it possible to combine the axes of illumination and detection. The illumination ring and the camera were equipped with rotatable broadband linear polarizers fixed at the crossed position to reduce specular reflection from the measured object. A 3D model of the unit was implemented using CAD software and printed out with a 3D material printer. The measurement approach considered allows the capture of the reflected signal of the entire FOV at a certain waveband. The scanning is performed in the spectral domain. Generally, the constructed device is capable of recording spatially and spectrally resolved reflectance used for further ANN analysis. Thus, diffuse reflectance is recorded with a spectral step of 5 nm from an area of 8 × 8 cm2 at 1010 × 1010 pixels resolution by the CMOS sensor. Normalized spatially resolved tissue reflectance is calculated as a pointwise ratio of dark-noise-corrected light intensity reflected from the object to that reflected from the diffuse reflectance standard. A hypercube from the reflectance standard is recorded every time before the measurement of an object. Gray Spectralon (50% reflection, Labsphere, Inc., USA) is used as a calibration standard. Use of the gray standard allows us to avoid the possible oversaturation of the CMOS sensor matrix for white reflectance standard (100% reflection) at a fixed integration time.
Calibrating UVA reflectance photographs – standardisation using a low-cost method
Published in Journal of Visual Communication in Medicine, 2018
What is needed for UVA photography are standards which exhibit minimal change in reflectance across the wavelength range to be imaged. Research grade commercial target standards exist which fit this description - Spectralon® diffuse reflectance standards. These offer optically neutral calibration targets and are available in predetermined reflectances between 2% and 99%, suitable between 250 nm and 2500 nm [https://www.labsphere.com/labsphere-products-solutions/materials-coatings-2/targets-standards/diffuse-reflectance-standards/diffuse-reflectance-standards/]. These standards are, however, costly especially if targets with a range of reflectances are required, or if a custom reflectance is required, and as such are outside the price range of many users. Another target created for UV imaging is Target-UVTM/UV-GrayTM, although this is more aimed at UV fluorescence imaging than UV reflectance [http://www.uvinnovations.com/]. As with the Spectralon® these are expensive for most users and are only recommended with certain filters and light sources.