利用Zernike Moment來偵測影像旋轉的角度與縮放的倍率，必須要求影像的完整性，一但影像受到破壞再旋轉或是旋轉之後受到破壞，Zernike Moment則無法計算出影像旋轉的角度，無法抵抗雙重攻擊。因此，本文提出以影像的中心為圓心，以固定的半徑往外延伸，計算每一個甜甜圈的Zernike Moment值；再利用排序法，選出間距較小的角度，則可計算出影像所旋轉的角度，即使旋轉後某些部分受到破壞或受到破壞後再旋轉，仍可利用沒有遭受破壞的Zernike Moment值，來求得影像旋轉的角度，進而抵抗雙重攻擊。 In many printer and publishing applications, it is desirable to embed data in halftone images for copyright control and authentication purposes. However, the robustness of the geometrical attacks in halftone watermarking is still a key problem.
In this paper, we proposed a multipurpose color halftone and halftone watermarking using embedding watermark into the pixel with complicated texture by wavelet transform based on the dithering technique in the halftone processing. For the color image. According to properties of the color model [R,G,B], we chosen the G level for embedded our robust watermark and B level for embedded our semi-fragile watermark. The Zernike moment is adopted to detect rotation and scale of the watermarked image. Experimental results show that watermarked image with good visual quality and the robust watermark is robust to the malicious attacks such as compress, corrupting, cropping, rotating, and scaling. The semi-fragile watermark can detect the regions where attacked by corrupted and cropped.
For gray-level image, the robust watermark is embedded by using two dither cells which produced different patterns during the halftone processing. We can find out the attacked regions of the image by using two new dither cells which are similar to the original dither cells. Robust watermark is robust to the malicious attacks such as corrupting, cropping, rotating, and scaling. The Correct DR value can close to 0.75 after the attack of print&scan. The semi-fragile watermark can detect the attacked regions and doesn’t need to modify the image. The advantage is to maintain the quality of the halftone image.
