What exactly does that mean? You mean you want a 1-D list of all pixel values outside one of the contour lines? The contour line at which level? Then do this:
mask = NT < someValue; % or >
pixelValues = NT(mask); % A 1-D list of all pixels below someValue.
Or do you want to mask the image, like you want a 2-D image but want the inside of the contour blackened or set to some other value like 1 or 255 or inf or nan? Like
NT(mask) = someValue; % For example NT(mask) = 0;
