**Han-Yan Wu \*, Ling-Hwei Chen and Yu-Tai Ching**

Department of Computer Science, National Chiao Tung University, Hsinchu 300, Taiwan; lhchen@cc.nctu.edu.tw (L.-H.C.); ytc@cs.nctu.edu.tw (Y.-T.C.) **\*** Correspondence: hywu.cs02g@nctu.edu.tw

Received: 11 October 2020; Accepted: 2 November 2020; Published: 4 November 2020

**Abstract:** The primary goal of steganographic methods is to develop statically undetectable methods with high steganographic capacity. The embedding efficiency is one kind of measure for undetectability. Block-based steganography methods have been proposed for achieving higher embedding efficiency under limited embedding capacity. However, in these methods, some blocks with larger embedding distortions are skipped, and a location map is usually incorporated into these methods to record the embedding status of each block. This reduces the embedding capacity for secret messages. In this study, we proposed a block-based steganography method without a location map for palette images. In this method, multiple secret bits can be embedded in a block by modifying at most one pixel with minimal embedding distortion; this enables each block to be used for data embedding; thus, our method provides higher embedding capacity. Furthermore, under the same capacity, the estimated and experimental embedding efficiencies of the proposed method are compared with those of Imaizumi et al. and Aryal et al.'s methods; the comparisons indicate that the proposed method has higher embedding efficiency than Imaizumi et al. and Aryal et al.'s methods.

**Keywords:** block embedding; embedding capacity; embedding efficiency; optimal selection; parity assignment
