RELATIONSHIP BETWEEN RGB COMPONENTS AND PIGMENT CONTENTS IN RICE LEAF

An attempt was taken to establish a methematical model for measuring the relation between RGB components of rice leaf colors and the content changes of various pigments. For this purpose the pigment content values of the leaves at different leaf positions and the values of their image RGB components at each growth stage of rice were studied. Besides curve fitting for describing the relationship between these two types of the values were adopted. The curves showed that the largest component value of the RGB was G; the second was R; and B was the smallest. Their mathematic models can perfectly describe the changes of leaf colors in rice. This study demonstrates that it is a approximate linear correlation between RGB components of rice leaf and its chlorophyll contents, facilitating the modelling and simulation of color changes of rice leaf. Introduction With the development of inter-discipline approach between computer science and agriculture recently, the research on information technologies of crop growth has inspired many scholars (Cao et al. 2006, Schnable and Springer 2013, Gai et al. 2015). Rice researchers made lots of researches on the relation between rice leaf colors and nitrogen levels (Wang et al. 2002, Zhao et al. 2006, Jiang et al. 2012, Tang et al. 2014), which provide a theoretical basis for the nitrogen nutrition diagnosis of rice and reasonable nitrogen application. With the development of digital agriculture, scientists on crop modelling studied changes of leaf color to create virtual rice growth models. Through obtaining the SPAD values of leaves at different rice growth stages, the dynamic changes of leaf color at different leaf positions of rice stems to establish color simulation models of rice leaf based on SPAD values (Chang et al. 2007, Zhu et al. 2008, Wang et al. 2010, Vollmann et al. 2011, Yi et al. 2016a). The change of leaf color is one of the important physiological indexes for reflecting the abundance or deficiency of nutrition in rice growth process, thus it becomes an indicator of rice cultivation. As the research data reveal, leaf colors of plant are related with the contained pigments in leaves, and proportions of the various pigment contents are a key of the color composition. The contained pigments in rice leaf mainly include chlorophyll a, chlorophyll b and carotenoid (xanthophyll and carotene), where chlorophyll a presents blue-green; chlorophyll b presents yellow-green; and carotenoid presents yellow (Feng 2007, Zhu et al. 2009, Wang et al. 2016). When rice reaches at the tillering stage, the sum of chlorophyll a and chlorophyll b in leaves is far more than carotenoid, making the leaves green. At this stage, the photosynthesis of leaves is strong, which is conductive for the rice growth. When the external environmental conditions such as temperature, moisture, nutrition, and other factors are changed or the rice enters the mature stage, the leaf pigment contents and their proportions will be updated. The degradation speed of chlorophyll a is higher than chlorophyll b, and the leaves gradually turn yellow. Meanwhile, while *Author for correspondence: . Faculty of Computer Science and Technology, Saint Petersburg Electrotechnical University "LETI", Saint Petersburg 197376, Russia.