Quantization of Wavelet Coefficients

"Adaptive Quantization of Wavelet Packet Coefficients for Embedding and Extraction of Digital Watermarks ":

Abstract—In this paper, a robust digital image watermarking
approach of embedding and extraction of digital watermarks using
adaptive quantization of wavelet packet coefficients was proposed.
The original image is decomposed by discrete wavelet packet
transform and the dominant wavelet coefficients are selected for
watermark embedding from each sub-band except the lowest
frequency one. Then, each watermark bit is adaptively embedded
with different strength into the selected wavelet packet coefficients
based on the odd or even value after quantization.