Reversible image watermark method based on quantized DCT coefficient zero values index

Abstract

A reversible image watermark method based on quantized DCT coefficient zero values index includes a watermark embedding process, a watermark extraction process and an image recovery process; wherein the watermark embedding can be applied in two modes: embedding is carried out during the process in which pixel image is compressed into JPEG image, or embedding is carried out in coded JPEG image. Specific embedding process aiming at mode I includes: (1) the original image is preprocessed, namely blocking (the size of block is generally 8*8), DCT transforming (discrete cosine transform) and quantization, thus obtaining quantized DCT block; (2) index value of medium-high frequency zero coefficient of the quantized DCT block is used for watermark embedding, and non zero coefficient probably generating ambiguity at extraction end is modified; (3) losses coding, such as run length coding and entropy coding, is carried out on the quantized DCT block embedded with watermark to obtain JPEG image; in the extraction process, the medium-high frequency coefficient index value of the quantized DCT block is utilized to extract watermark and recover the original image without loss by inverse operation of embedding method; the embedding and extraction process of mode II is similar. The invention has reversibility, reduces the ratio of the modified coefficient and embedded watermark digit, and can embed massive watermarks while causing less distortion.

Description

technical field [0001] The invention relates to a method for embedding and extracting a reversible image watermark, in particular to a method for reversible image watermarking based on quantized DCT coefficient zero value index. Background technique [0002] The digital information revolution has brought profound changes to human society and life, as well as new challenges and opportunities for innovation. The perfect duplication of digital multimedia works and the almost cost-free distribution around the world make digital copyright protection and content integrity verification and other security issues an urgent problem to be solved. Digital watermark hides some information in digital image, video or audio signal, and has become an effective means to protect the security of digital media content. In most of the existing digital watermarking methods, due to the introduction of the watermark signal, the host media will be permanently changed and cannot be restored to the st...

AI Technical Summary

Problems solved by technology

Chang et al. define a set of sequences in each block of quantized DCT coefficients and use consecutive zero values ​​in the sequences to achieve watermark embedding (see Chang, C.-C., et al., Reversible hiding in DCT-based compressed images. Information Sciences, 2007.177(13): p.2768-2786), achieved a large embedding capacity with the introduction of lower distortion, but there are also some limitations: in order to embed a bit of watermark data, at least one zero coefficient may be Modification, and modifying zero coefficients will lead to a decrease in image quality. In addition, for some images compressed with high JPEG quality, or images with complex content, the probability of continuous zero coefficients in their quantized DCT coefficient blocks will become smaller, which will reduce Embedding capacity of the algorithm in these images

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