Abstract
This paper describes the robustness of watermark using CGH (Computer-Generated Hologram). Watermark is one of technology for protect of copyright. The watermark using Lohmann type CGH has investigated, however that of another type CGHs is not investigated. In this paper, the robustness of watermarks using four CGHs (type : Lohmann, Lee, binary kinoform, err-diffusion) was compared. The robustness was influenced by form of CGH's aparture, and the point at issue solved by changing it.
