Bull. Jpn. Soc. Fish. Oceanogr. 77(4), Page 274-281, 2013   Development of a method to evaluate the color tone of raw nori (Pyropia yezoensis) by using a digital camera and image analysis Asataro Tsuge1, 3, Akihiko Ohashi2, 4, Yasuo Nakashima1, Yoshio Takeuchi1, 4, Satoshi Yamada1 and Yasuhiro Iwata1 1 Aichi Fisheries Research Institute, 97 Wakamiya, Miya, Gamagori, Aichi 443-0021, Japan 2 Higashimikawa Agriculture, Forestry and Fisheries Office, Aichi Prefectural Government, 5-4 Hatcho-dori, Toyohashi, Aichi 440-0806, Japan 3 Present: Aichi Fish Farming Institute, Aichi Fisheries Promotion Fund, 1-3 Ichizenmatsu, Konakayama, Tahara, Aichi 441-3618, Japan 4 Present: Fisheries, Administration Division Department of Agriculture, Forestry and Fisheries Aichi Prefectural Government, 3-1-2 Sannomaru, Naka-ku, Nagoya, Aichi 460-8501, Japan † E-mail: asatarou0301@hotmail.co.jp We developed a method for evaluating the color tone of raw nori (Pyropia yezoensis) by using a digital camera and image analysis. The RGB values of raw nori were derived from images taken using a digital camera, and then image analysis was performed using the freeware Lia32 (http://www.agr.nagoya-u.ac.jp/~shinkan/LIA32/index.html). As a result, the RGB values obtained using 2 different digital cameras were highly correlated. The G value derived using this method was highly correlated with the L* value, which is the measured colorimeter value, and nitrogen content of nori (L*: r=-0.865, nitrogen content: r=0.528). We converted the L* values into G values, and the G values into nitrogen contents using regression equations. As a result, G values below 20 and nitrogen contents below 47 μg・mg DW-1 were determined to indicate discoloration of nori. Key words: nori, color tone, Mikawa Bay