what will the formula for mean intensity value of RGB image

gray scale image intensity value is

m=mean2(I)
then what will be of RGB image

Answer 1

[Image Analyst]

The help says

mean2 computes the mean of an array A using mean(A(:)).

So that pretty much answers your question. It will average everything together regardless of which color plane a value is in. It does not give a weighted mean, like rgb2gray(), nor does it give a 3-element array with means of each color channel separately.