After the spectral measurements, red-green-blue (RGB) photographs of the tree were taken in the same 47 view angles as used for the spectral measurements. An additional photograph was taken in the direction of the illumination, while the lamp was moved away to allow the camera to see the tree. The photographs in the view angles were used for calculating STAR, and the photograph in the direction of illumination was used for normalizing the measured spectra to the amount of radiation intercepted by the tree. The photography was performed with a Nikon D5000 camera with an adjustable lens that had focal length set at 45 mm. The camera was attached to the goniometer next to the detector unit of the spectrometer: the view zenith angles of the camera and spectrometer differed 3°, because the physical dimensions of the camera did not allow it to be placed exactly at the same position with the spectrometer. During the photography, the tree was illuminated from both sides with two LED lamps (2 × 10 W each), and a white canvas was placed on the background. This enabled the silhouette of the tree to be separated from the background in data processing. The camera was remotely triggered, and the f-number was f/8. To avoid saturation of the photos, exposure time was manually set for each azimuth by underexposing the white background by 0.7 exposure stops, using the built-in light meter of the camera. Photographs taken with −0.7 and +0.7 exposure stops from this default level were always taken also. These additional photographs were only used in evaluating the effect of exposure time on the results [2], and are not included in the data described in Table 1.

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