  Reversible data hiding in encrypted image (RDHEI) becomes a hot topic, and a
lot of algorithms have been proposed to optimize this technology. However,
these algorithms cannot achieve strong embedding capacity. Thus, in this paper,
we propose an advanced RDHEI scheme based on lossless pixel conversion (LPC).
Different from the previous RDHEI algorithms, LPC is inspired by the planar map
coloring question, and it performs a dynamic image division process to divide
the original image into irregular regions instead of regular blocks as in the
previous RDHEI algorithms. In the process of LPC, pixel conversion is performed
by region; that is, pixels in the same regions are converted to the same
conversion values, which will occupy a smaller size, and then the available
room can be reserved to accommodate additional data. LPC is a reversible
process, so the original image can be losslessly recovered on the receiver
side. Experimental results show that the embedding capacity of the proposed
scheme outperforms the existing RDHEI algorithms.
