Digital halftoning

© Springer Nature Singapore Pte Ltd. 2020. Chapter 2 focuses on binary secret image. In the next four chapters, we move further to grayscale secret images and cover images. For this case, the shares and the decrypted images are halftone images. This chapter will equip the readers with necessary background knowledge of digital halftoning. First, the problem of halftoning and its classification are introduced. Then, we review three popular halftoning frameworks, including ordered dithering, error diffusion, and direct binary search (DBS). The mathematical models for error diffusion are also discussed. Finally, some commonly used perceptual quality measures for halftone images are introduced. These measures are particularly useful when developing algorithms for grayscale images in later chapters.