Mean,std dev and var of an image

how to find the mean,standard deviation and variance of an image??

i have tried the following code in MATLAB. can i get to know whether it's correct or not??

r_ch=file😀,:,1);
g_ch=file😀,:,2);
b_ch=file😀,:,3);
r_m=mean(mean(r_ch));
g_m=mean(mean(g_ch));
b_m=mean(mean(b_ch));
r_v=var(var(double(r_ch)));
g_v=var(var(double(g_ch)));
b_v=var(var(double(b_ch)));
r_s=std(std(double(r_ch)));
g_s=std(std(double(g_ch)));
b_s=std(std(double(b_ch)));