A steganographic scheme based on perfect coverings of dichotomous shares with sparse observation windows is presented in this paper. The manipulations with pixels are based on the number of different colours in the sparse cells of the current observation window. The conditions for the existence of perfect coverings for different architectures of sparse observation windows are derived. The number and distribution of active cells in the current observation window contribute to the additional security of the proposed scheme. This paper also provides performance measures, statistical features, and demonstrates the robustness of the proposed steganographic scheme.