<P> Countershading was described in the US War Department's 1943 Principles of Camouflage, where after four paragraphs of theory and one on its use in nature, the advice given is </P> <P> Upper surfaces should be painted and textured so as to conform to the color and tone of the surrounding country (background) and the sides graded and toned from this to the white which the under surfaces and parts in shade should be painted . </P> <P> Inventors have continued to advocate military usage of countershading, with for example a 2005 US patent for personal camouflage including countershading in the form of "statistical countercoloring" with varying sizes of rounded dark patches on a lighter ground . </P> <P> Research by Ariel Tankus and Yehezkel Yeshurun investigating "camouflage breaking", the automated detection of objects such as tanks, showed that analysing images for convexity by looking for graded shadows can "break very strong camouflage, which might delude even human viewers ." More precisely, images are searched for places where the gradient of brightness crosses zero, such as the line where a shadow stops becoming darker and starts to become lighter again . The technique defeated camouflage using disruption of edges, but the authors observed that animals with Thayer countershading are using "counter-measures to convexity based detectors", which implied "predators who use convexity based detectors ." </P>

What is camouflage counter shading and other techniques used by fish as defense