Various types of visible watermarks, such as opaque monochrome and translucent full color ones, can be embedded through this scheme. In , a generic visible image watermarking with the capability of lossless recovery was presented, which was based on the deterministic one-to-one compound mappings of pixel values for overlaying a variety of visible watermarks with different sizes on original images. In order to achieve the reversibility, an encoded packet of reconstruction/recovery data was reversibly embedded into the non-visibly-watermarked area. transparently revealed the watermark image by overlapping it on a user-specified area of the original image through adaptively adjusting the pixel values beneath the watermark . Based on the scaling factors of human visual system (HVS), Yang et al. Both the two schemes and required the original watermark during the procedure of image recovery. For the sake of recovering the original image correctly, a reconstructed packet was embedded into the watermarked image. In the scheme , the pixels of the original image were mapped into a certain range in order to visualize the watermark. proposed lossless visible watermarking methods that rotated the successive pixels of watermark image to insert a visible bit . But, the watermarked image in this scheme was somewhat blurred. proposed a visible and reversible watermarking scheme, which modified the remarkable bitplane in the original image and compressed the modified bitplane into the non-watermarked region. Therefore, the visible and reversible watermarking scheme deserves in-depth investigation,, ,, ,, ,, ]. However, former visible watermarking schemes are often irreversible, which means the original image cannot be reversed due to the modifications caused by the inserted visible watermark. The invisible and reversible watermarking schemes aim to achieve larger hiding capacity and better visual quality of stego image under the condition of reversibility.Īnother kind of watermarking scheme that adds the watermark logo on the cover image visibly, i.e., visible watermarking, is more intuitive and convenient to identify the ownership information or indicate image labeling compared with invisible watermarking, because it can be directly recognized by human eyes rather than a watermark decoder. proposed a HS based algorithm , which utilized the peak point and zero point in the histogram to embed the watermark information. in , which splitted the host image into a series of pixel pairs and the difference of each pixel pair can be inserted with one-bit information. The DE based algorithm was first proposed by Tian et al. The existing, invisible and reversible watermarking schemes are usually based on three mechanisms, i.e., lossless compression , ], difference expansion (DE) ,, ,, ] and histogram shifting (HS) ,, ,, , ]. That is to say, the embedded watermark for image tagging or labeling is invisible. According to whether the stego image can be exactly recovered to its original version or not, watermarking schemes can be categorized as reversible watermarking ,, , ] and irreversible watermarking, ].Ĭurrently, most of reversible watermarking schemes were studied to embed the watermark information into cover image in a imperceptible way. As an effective technique that embeds information into images for copyright protection, image watermarking has been widely studied. In recent years, many scholars have paid great attention to the research of multimedia information security, especially for digital images in military and medical applications ,, ,, , ]. Experimental results demonstrate the effectiveness and superiority of our schemes. In addition, for both two proposed schemes, the invalid user without the knowledge of secret key cannot achieve reversible recovery for original image. The scheme can perfectly remove the embedded visible watermark and can also exactly recover original image with the assist of image inpainting technique. In the second scheme, the scenario of visible-watermark removal for the image generated by any visible watermarking algorithms (no matter the sender and the receiver know the algorithms or not) is considered. After embedding the difference information invisibly and reversibly, the final embedded image can be exactly recovered to its original version after visible-watermark removal, which avoids the problem of overflow and underflow in Chen et al. A run-length coding based method is utilized to compress the difference between the preliminary recovered image and original image. In the first scheme, we consider the scenario for the image generated by a specific visible (not completely reversible) watermarking algorithm Chen et al. In this paper, we propose two schemes for visible-watermark removal and reversible image recovery.
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