Fig. 2

Illustration of the Integral Histogram trick. Case of two bi-parameter axes, x and y; left: visualisation on the 2D integration or summation domain associated to \(\mathbb {J}(M)\) value; right: illustration of the computation of the integral (sum) on any rectangular domain ABDC by finite difference between \(\mathbb {J}\) values at its four corners: \(\mathbb {J}(D)-\mathbb {J}(C)-\mathbb {J}(B)+\mathbb {J}(A)\)