Skewed distribution of leaf color RGB model and application of skewed parameters in leaf color description model

Table 1 Parameters using skewed-distribution analysis and the SPAD values

Parameter	40 days	50 days	60 days	65 days
SPAD	25.02b	32.45c	25.56b	10.95a
R_Mean	98.64a	102.38b	121.78c	154.62d
R_Median	94.96a	104.88b	123.68c	158.68d
R_Mode	88.32a	118.02b	131.64c	170.62d
R_Skewness	0.46d	− 0.04c	− 0.19b	− 0.59a
R_Kurtosis	0.14b	0.26b	− 0.07a	0.12b
G_Mean	126.58a	126.98a	138.96b	149.80c
G_Median	123.02a	130.26b	141.30c	153.14d
G_Mode	114.72a	137.50b	146.60c	163.82d
G_Skewness	0.35d	− 0.29c	− 0.36b	− 0.59a
G_Kurtosis	0.37b	0.43b	0.06a	0.51b
B_Mean	32.60a	37.34b	39.65b	44.82c
B_Median	21.92a	34.48b	36.54b	41.74c
B_Mode	12.32a	24.82b	27.14b	34.28c
B_Skewness	1.83b	1.48a	1.65ab	2.10c
B_Kurtosis	3.70a	7.13b	8.85b	13.32c
Y_Mean	107.47a	109.38a	122.49b	139.28c
Y_Median	103.14a	111.88b	124.16c	142.30d
Y_Mode	95.08a	118.38b	127.96c	152.66d
Y_Skewness	0.54d	− 0.09c	− 0.20b	− 0.44a
Y_Kurtosis	0.39b	0.42b	0.05a	0.44b

The 20 parameters include the mean, median, mode, skewness and kurtosis with the red, green, and blue color channels as well as the gray-level images with MATLAB using 50 pieces of fully expanded tobacco leaves at 40, 50, 60 and 65 days, respectively. The SPAD values also come from the 50 leaves for each leaf age. Each leaf blade was measured at five points: one on the upper part, two at the middle part and two at petiole of both leaf sides. Values without a common letter are significantly different according to the Duncan test (p < 0.05)