color distribution in L*a*b*

I got the histogram of a* channel of a pic. I wanna know the region distribution. For example, which are the regions with a*<0 and where are a*>0. Is there anyway to do this?

Answer 1

[madhan ravi]

a(a<0)
a(a>0)

[ZHI QU]

Thx Madhan. I should be more clear, I want to segment the pic according to the a* value.

[Juan Villacrés]

If you want to segment the image:

% Define the mask according the "a" channel
mask = Ioriginal(:,:,2)<0;    % a value
% Multiply the image with the mask in the three channels
Inew = Ioriginal.*repmat(mask,[1,1,3]);