# A Survey on Robust Video Watermarking Algorithms for Copyright Protection
## 4 Robust Watermarking Algorithms Based on Original Videos
### Video Watermarking in Spatial Domain  
Video watermarking algorithms in spatial domain usually embed the watermark directly into the luminance or chrominance components of the original video, which often have two prominent characteristics: low complexity and high payload. The main spatial domain methods include least significant bit (LSB) modification [23], spread spectrum modulation [24], and so on. Among them, the LSB method is the most classical embedding method, which embeds the watermark into the LSB of the component. [PERSON] and [PERSON] [25] proposed an invisible video watermarking algorithm using an optimized LSB technique. A pseudorandom number generator and secret key are used to improve the secure of the algorithm. Although LSB substitution is an extremely simple technique, its robustness is very poor. To improve the robustness, [PERSON] et al. [26] proposed a multi-sprites dynamic video watermarking algorithm based on speed-up robust features (SURF), which can effectively resist collusion and transcoding attacks. The watermark information is embedded into three YUV color space components by modifying the middle significant bit (MIDSB) and LSB, which can provide high level of robustness and invisibility.  
Watermarking algorithms based on the spread spectrum are also effective spatial domain algorithms. The original video frames are scanned according to orders to obtain a one-dimensional signal, and the watermark information is modulated into pseudorandom sequences by spread spectrum technology and embedded in the video signal [27]. In a previous paper [28], the watermark was expanded to the same size as the video frame, and then embedded frame by frame. Since the same watermarks in different frames amplify each other during the averaging process, the proposed scheme can resist frame averaging attacks. To improve the robustness to different attacks, [PERSON] and [PERSON] [29] introduced cyclic error correction codes to resist bit errors of watermark. Spread spectrum is adopted to spread the power spectrum of the watermark. Spatial redundancy is used to embed the spread watermark in luminance pixels and temporal redundancy is used to embed the same watermark in each frame of each group.  
There are also many other robust video watermarking algorithms in spatial domain. For example, [PERSON] et al. [30] decomposed the grayscale watermark image into eight bit-plane images and embedded them into different scenes of original video. Some pixel values of Y component in video frames are selected and grouped, and the watermark is embedded by adjusting the relative relationships of pixel values in every group. [PERSON] and [PERSON] [31] proposed a semi-blind video watermarking algorithm based on SURF and block classification. The best frames of each shot and the best regions or blocks of best frames, which are robust to resist multiple attacks, can be selected using shot segmentation and attack tests. The block classification technique based on canny edge detection is adopted to divide selected robust blocks into two kinds: edge blocks and flat blocks. Then, the owner's share information can be obtained by combining the classification results and watermark information. To resist scalable recompression and transcoding attacks, a robust video watermarking algorithm based on a spatial uniform mapping model was proposed by [PERSON] et al. [32]. Frames before scene change are selected for embedding using histogram difference method, which can resist the aimless frame dropping attack. The binary image with fixed size is processed by Arnold transform, and then uniformly embedded into the blue component of selected frames through a spatial random mapping algorithm.  
Watermarking algorithms in spatial domain are widely used in the early stage due to its low complexity. However, with the development of video coding technology, its robustness is poor and thus its application scope is limited. The summary comparison of several watermarking algorithms in spatial domain is shown in Table 2.