The sharpening filters could boost the image by changing it look more defined. In this paper, a comparison is toke place between the effects two sharpening filters on the reliability of the watermark in spatial domain image watermarking. These sharpening filters are the Laplacian and the high boost. These filters are applied before preforming watermark recovery algorithms. The difference between the watermark information and host image is amplified by these filters. Thus, watermark could recover considerably better by watermark recovery algorithm. A typical correlation based method is used as a representative of spatial domain watermarking methods. Several experiments are done to compare the effectiveness of these filters on correlation based watermarking algorithm.
Keywords: Image Sharpening; Laplacian Filter; High Boost Filter; Digital Image Watermarking; Correlation Based Watermarking; Spatial Domain Watermarking.
With the expansion of the Internet, create the copy, transmit, and distribute the digital data becomes easy. Therefore, there is the high demand for trustworthy and secure copyright protection methods for digital data. The watermarking has been proposed as a valid solution for this problem. The purpose of the watermark is to insert some extra information about the digital data without visibly modifying it .
In the design of the watermarking algorithm always, there is a conflict between robustness and imperceptibility. The imperceptibility is the amount of decreases in signal quality; and the robustness is the ability of the watermark to persist readable after innocent or malicious signal processing operations on the watermarked image. These parameters are incompatible with each other, and they should be set to meet the requirements of the application , .
Generally, watermarking methods are classified into the spatial domain or the transform domain. Spatial domain techniques are not robust to image compression and other image processing , . Although some methods  utilized pre-filtering skill to increase reliability of the watermark recovery, experimental results have shown the weaknesses of spatial domain watermarking. Transform domain watermarking schemes like the Discrete Cosine Transform (DCT) ,  and the Discrete Wavelet Transform (DWT) ,  typically bring higher image imperceptibility and more robustness to image processing operations.
In order to increase the robustness of the Watermarking algorithms, there are two main methods: embedding watermark in more robust places, increase power of watermark retrieval algorithms.
In the first methods, there are an attempt to use human visual system characteristics to choose appropriate for resistance and transparency. These techniques generally utilize the frequency-domain characteristics to detect the most proper place to embed the watermark. These methods are commonly used in frequency domain watermarking techniques. There are several...