  Reversible contrast mapping (RCM) is a simple integer transform that applies
to pairs of pixels. For some pairs of pixels, RCM is invertible, even if the
least significant bits (LSBs) of the transformed pixels are lost. The data
space occupied by the LSBs is suitable for data hiding. The embedded
information bit-rates of the proposed spatial domain reversible watermarking
scheme are close to the highest bit-rates reported so far. The scheme does not
need additional data compression, and, in terms of mathematical complexity, it
appears to be the lowest complexity one proposed up to now. A very fast lookup
table implementation is proposed. Robustness against cropping can be ensured as
well.
