Electronics and Telecommunications Research Institute

Seon Hwa Lee

Sanghyun Joo

Young Ho Suh

Yong Seok Seo

A for embedding a digital watermark on a wavelet lowest subband includes: setting a DC component region of a multi-stage wavelet-transformed original copy image to a watermark embedment region, and high-frequency filtering an original picture LLof the embedment region; generating index information for designating a pixel position, and a watermark sequence to be embedded; calculating an embedment strength &#x3bb; for each position of the watermark embedment region; in case the watermark sequence is sequentially embedded on an embedded position designated by the index information, mutually comparing the original picture LLcoefficient value for each embedded position with a mirror picture LL' coefficient value, and then altering the original picture LLcoefficient value; and in case the original picture LLcoefficient value is differentiated above a predetermined value with reference to the coffesponding embedment strength &#x3bb;, skipping the watermark embedment for the position.

Method for embedding and extracting digital watermark on lowest wavelet subband

The present invention relates to a method for blindly embedding and extracting a watermark by using wavelet transform and a human visual system (HVS) model, which obtains both robustness and invisibility by applying the HVS model of NVF or JND imitating a human visual system to a middle frequency band for wavelet transformation and using a quantization step determined adaptively according to the importance of wavelet coefficient. A method according to the present invention includes the steps of: decomposing an original image by a wavelet and selecting a middle frequency band as a watermark embedment area; obtaining an HVS model having a human visual recognition information at each embedding position; determining the importance of the coefficient for each embedding position, and adaptively determining a quantization step for each embedment location by using the importance and the HVS model; quantizing each pair of embedment area by the quantization step and variably embedding a watermark sequence into a middle frequency band according to a value of the watermark; and performing inverse wavelet transform on an overall area into which the watermark sequence is embedded, and generating a watermarked image.

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Taejon, South Korea

Seon Hwa Lee