# Robust Template-Based Watermarking for DIBR 3D Images
## 1 Introduction
Because of the object matching with SIFT, these methods were robust to DIBR distortion. Additionally, the methods showed high robustness to both general signal distortions and geometric distortions. However, SIFT-based DIBR watermarking methods need SIFT descriptors during watermark extraction. These methods cannot extract watermarks blindly; therefore, SIFT-based watermarking methods are less practical than full-blind watermarking systems. [PERSON] et al. defined a dependent view region, which is a common area of the left and right eye images, and inserted a watermark using the DC coefficients of the DCT in the dependent view region [24]. This method achieved robustness against DIBR, JPEG compression and various noise attacks. [PERSON] et al. also proposed a 3D video watermarking technique [25]. This method exploits the shift invariance and the directional property of the 2D DT-DWT to insert a watermark. This technique showed high invisibility and high robustness against 3D-high efficiency video coding compression, as well as DIBR attacks. However, neither of these methods consider geometric distortions. [PERSON] et al. proposed a DT-CWT-based video watermarking method using color channels [26,27]. The method inserted a watermark into the U channel of the YUV color space and inserted the same watermark rotated 180\({}^{\circ}\) into the V channel. They showed that the method was robust to DIBR, due to the DT-CWT domain characteristics; and geometric attacks, such as scaling and rotation, since the U and V channels suffer the same geometric transformation. However, if the image center were changed due to attacks such as crop or translation, the watermark could not be detected, and under geometric distortion, it could only determine whether a watermark had been inserted or not, i.e., an on/off switch. Therefore, its application was somewhat limited. Various templates have been proposed that are robust against geometric attacks [28, 29, 30, 31]. However, these are only designed to be robust to linear distortions, such as affine transforms, and so are not robust to DIBR, which is a non-linear distortion, as discussed above. The results of previous works show that blind watermarks have great difficulty surviving in geometrically-distorted DIBR images, because the watermark must be robust to both DIBR and geometric attacks, as shown in Figure 1. The combination of non-linear and linear deformation severely damages most watermarking domains. Therefore, it is desirable to solve this problem by combining two watermarking methods that have different characteristics, rather than using a single watermarking method. This paper proposes a blind template-based watermarking system combining templates and message watermarks. The role of the template is to restore geometric distortion without being destroyed by the DIBR attack. The template is inserted into the curvelet domain in the form of peak points, and geometric distortion is estimated using the modified iterative closest point (ICP) method. The message watermark inserts and detects messages in the DIBR image. The proposed message watermark is inserted into the 1D-DCT domain, and the message is extracted from the DIBR image after geometric distortion recovery using the proposed template. The message watermark inserts the same information along the horizontal direction in the 1D-DCT domain, and the inserted message watermark is invariant to DIBR due to 1D-DCT linearity. Experimental results showed that the proposed method has both high invisibility and robustness against various attacks. It achieved excellent scores in visual quality tests and low BER for common signal distortions, such as noise addition and JPEG compression. The watermarking system also exhibited good robustness against geometric distortions, a point of vulnerability in previous approaches, and excellent robustness against DIBR attacks and DIBR configuration adjustments. This paper is organized as follows.