1. A method of digitally printing with a single colorant a security feature imperceptible to the naked eye, comprising: printing, with the single colorant, first and second patterns of binary pixels of a digital security image, the image having a first region formed by the first pattern and an abutting second region formed by the different second pattern, the first and second printed regions each having a gray level; determining a darker one of the first and second printed patterns; printing the security image with the single colorant, the region corresponding to the darker printed pattern printed at a reduced gray level such that the printed first and second regions appear substantially indistinguishable to the naked eye.