Fig. 4
From: Development of an accurate low cost NDVI imaging system for assessing plant health
Example data showing calibration and normalization. A Calibration of raw digital number, direct from images captured by a camera, using the known reflectances of the six calibration materials to find the relationship between digital number and reflectance. Once the relationship is established for an image, raw digital number for the entire image can be converted into values of reflectance. B Normalization of reflectance data, by re-scaling the converted reflectance values (from 0 to 100%) to use the full 16 bit (0–65,535) range. C, D A typical NIR image, demonstrating the visual difference between images before (C) and after (D) the calibration and normalization process, with the image on the right now using the full range of the image, with image colour (from white to black) corresponding to actual values of reflectance