plz help me to understand this loop

for color_idx=1:3
    img_tmp = img_in_lin(:,:,color_idx);
    img_tmp = img_tmp(textureless_map);
    % Estimate the veiling-light to be the median value in the region.
    A(color_idx) = img_tmp(idx_median);
end

Answer 1

[KSSV]

for color_idx=1:3     % loop for each color channel Red, Blue, GReen
    img_tmp = img_in_lin(:,:,color_idx);     % This extracts the color channel 
    img_tmp = img_tmp(textureless_map);      % From the color channle pick the pixel values at indices textureless_map 
    % Estimate the veiling-light to be the median value in the region.
    A(color_idx) = img_tmp(idx_median);     
end