human: Given a node-centered hypergraph: <hypergraph>, where nodes represent authors and hyperedges represent groups of authors who co-authored the same paper.

Details of the hypergraph:
Center node: "Watermarking Document Images with Bounding Box Expansion"
  Abstract: Imperceptible displacements of text objects has been shown to be a successful technique for hiding data in document images. In this paper we extend our earlier work to show how the height of a bounding box enclosing a group of text words can be used to increase the density of information hidden on a page. We present experimental results which show that bounding box expansions as small as 1/300 inch can be reliably detected, even after the distortions introduced by noisy image reproduction devices such as plain paper copiers. Digital watermarks based on this technique can be used with electronically disseminated documents for applications including copyright protection, authentication, and tagging.

Connected through hyperedge HE-1 (induced by source paper "Secure spread spectrum watermarking for multimedia"):
  with members:
    - "Reversible data hiding"
    - "Quantization Index Modulation Methods for Digital Watermarking and Information Embedding of Multimedia"
    - "Image steganalysis based on moments of characteristic functions using wavelet decomposition, prediction-error image, and neural network"
    - "Multiresolution scene-based video watermarking using perceptual models"

Question: Please tell me which research area the center author belongs to. The 4 classes are: Computer science, Mathematics, Engineering, Economics, Psychology, Business. Directly output the class name.

gpt: Computer science