Convolution in Image Processing
I'm going to use a grayscale image for simplicity. Suppose you have a 3D matrix and each slice is the result of filtering the image with the Gabor filter for that angle.

I = randn(256, 256); % Just some random image
G = gabor_filter; % Assume G is 256x256xNum_Angles, e.g. 256x256x6 if you had 6 angles
Y = zeros(256, 256, size(G, 3)); % Preallocate a temporary matrix

for idx = 1:size(G, 3)
    Y(:, :, idx) = conv2(I, G(:, :, idx), 'same');
end

Ymin = min(Y, [], 3); % This takes the minimum along the 3rd dimension