How to get to compute the standard deviation of a multispectral vector?

I have a vector that have the size of 598 x 598 x 7, where 7 is the number of bands. I need to perform some training data to work with the knnclasify command. To perform the training data I will use the normrnd command and I need to compute the mean and the standard deviation of the vector. I wrote the following code:

Data = lanread('flc1.lan'); % flc1.lan data

m = mean(Data);

Sigma = std(Data);

It seems that I can compute the mean but I get the following error on the standard deviation:

Error using var (line 65) First argument must be single or double.

Error in std (line 38) y = sqrt(var(varargin{:}));

Error in HW10 (line 14) Sigma = std(Data,0,7);

Can someone please help me with this? I don't understand what I'm doing wrong.