title: Pixel color clustering of multi-temporally acquired digital photographs of a rice canopy by luminosity-normalization and pseudo-red-green-blue color imaging.
abstract: Red-green-blue (RGB) channels of RGB digital photographs were loaded with luminosity-adjusted R, G, and completely white grayscale images, respectively (RGwhtB method), or R, G, and R + G (RGB yellow) grayscale images, respectively (RGrgbyB method), to adjust the brightness of the entire area of multi-temporally acquired color digital photographs of a rice canopy. From the RGwhtB or RGrgbyB pseudocolor image, cyan, magenta, CMYK yellow, black, L*, a*, and b* grayscale images were prepared. Using these grayscale images and R, G, and RGB yellow grayscale images, the luminosity-adjusted pixels of the canopy photographs were statistically clustered. With the RGrgbyB and the RGwhtB methods, seven and five major color clusters were given, respectively. The RGrgbyB method showed clear differences among three rice growth stages, and the vegetative stage was further divided into two substages. The RGwhtB method could not clearly discriminate between the second vegetative and midseason stages. The relative advantages of the RGrgbyB method were attributed to the R, G, B, magenta, yellow, L*, and a* grayscale images that contained richer information to show the colorimetrical differences among objects than those of the RGwhtB method. The comparison of rice canopy colors at different time points was enabled by the pseudocolor imaging method.
authors.affiliation: Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Doi
authors.affiliation: Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan ; Department of Civil and Environmental Engineering, Bogor Agricultural University, Kampus IPB Darmaga, Bogor 16680, Indonesia.
authors.forename: Chusnul
authors.initials: C
authors.lastname: Arif
authors.affiliation: Department of Civil and Environmental Engineering, Bogor Agricultural University, Kampus IPB Darmaga, Bogor 16680, Indonesia.
authors.forename: Budi Indra
authors.identifier: 0000-0002-6011-9447
authors.initials: BI
authors.lastname: Setiawan
authors.affiliation: Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Masaru
authors.identifier: 0000-0001-8175-4880
authors.initials: M
authors.lastname: Mizoguchi
mesh_terms: D016000:Cluster Analysis; D003116:Color; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D012275:Oryza / Q000254:growth & development*; D010781:Photography / Q000379:methods*