We use a simple automatic procedure to estimate all eight Neugenbauer
primaries for each page (in our experience there is some
variability between different pages of the same book). The idea is
to robustly estimate the extrema of the page’s color gamut. For example,
to estimate the color of the cyan primary we compute the
maximal value of the product (1−r)· g · b over the entire page, and
average the colors of those pixels for which this product is within 1
percent from the maximal value. The other primaries are estimated
in a similar fashion. In the supplementary material we include a
quantitative evaluation of this technique on ground truth data.