Steganography in halftone images

While gray-scale images can be readily displayed in computer monitors and other light-emitting displays, they also need to be displayed routinely in other reflective media such as newspaper, magazines, books, and other printed documents. However, in reflective media, the application of ink on the reflective media implies that only 1-bit images (with two tones: black and white) can be displayed. A problem arising from this is that straightforward 1-bit quantization on an image would lose most of the important image details. With such constraints, there is a class of image processing technique called image halftoning that converts an 8-bit image into an 1-bit image, which resembles the 8-bit image when viewed from a distance. Such 1-bit images are called halftone images [1]. Halftone image technologies are widely used in printed matters.