Image blending operation 'soft-dodge' (c = (cA+cB<1.0)?0.5*cA / (1.0 - cB):1.0-0.5*(1.0 - cB)/cA)
Irudi nahasketaren eragiketa: 'zuritze leuna' (c = (cA+cB<1.0)?0.5*cA / (1.0 - cB):1.0-0.5*(1.0 - cB)/cA)