Novel multi-bit quantum comparators and their application in image binarization

Quantum image processing has attracted much attention since it offers a potential solution to efficiently calculate some hard problems much faster than classical image processing. In particular, it is a basic operation to change each image pixel into black or white, named as a binary image. Here we present novel multi-bit quantum comparators to realize quantum image binarization. These comparators compare two quantum logic states and identify which of them is the largest. We analyze the superior performance of our proposed comparators in terms of quantum cost, quantum delay and auxiliary bits compared with the existing comparators. Furthermore, our quantum image binarization exploits the advantages of our proposed multi-bit comparators to change the values of image pixels into 0 or 255.