【文章內(nèi)容簡(jiǎn)介】 wo luma prediction modes that are assigned different responsibilities. First is the 44 luma prediction mode that is chosen for the detailed areas of the frame. Second is the 1616 luma prediction mode that is chosen for the smooth areas of the frame. After an intra prediction each 44 block of residual data is transformed by an integer transform. An integer transform means all operations can be carried out using integer arithmetic without loss of decoding accuracy. If the macroblock is coded in the 1616 intra prediction mode, the DC coefficients of all 44 blocks are transformed. This transformation is done by a 44 Hadamard transform after the 44 integer transform to decorrelate these coefficients futher. The watermark is embedded in one quantized coefficient of a macroblock by the proposed video watermarking algorithm. The quantized coefficient, iA for watermark embedding process is randomly selected. This is what guarantees the security of the proposed algorithm in this project. Visible artifacts are not induced by embedding the watermark in only one quantized coefficient in a macroblock. Even though, the attacker cannot identify which quantized coefficient has been chosen .If he wants to the make watermark detection impossible, then he has to change at least half of the quantized coefficients. The video will be useless due to visible artifacts in the video sequence in case half of the quantized coefficients are changed. iA is the quantized AC coefficient selected in the MB for watermark embedding process by using several bits of the ikP . The ikP controls the selection of the quantized AC coefficient iA in the thi macroblock for watermark embedding process. A proposed video watermarking algorithm in this project can be under selfcollusion attack in case the same ikP is used for every video frame, although this would be of an advantage due to transmission of a very short ikP . To resolve this kind of dispute, we need to have several different ikP utilized for every video frame. This would solve the dispute on one hand but also create another dispute on the other hand. The created dispute is that, in this case we need a very long ikP key to be transmitted. The danger of transmitting a very long ikP key is the impracticability of our proposed video watermarking algorithm for in the pressed domain. A dispute of this nature is now resolved by generating the general key, ikG from a bination of a public key, ikP and a secret key, kS . The ikP is extracted from some robust characteristic of the macroblock and a kS is possessed by the copyright owner as shown in the figure . From each macroblock the ikP is extracted. ikP is passed to a cryptographic system in the plaintext form with the kS . The cryptographic system generates a ciphertext which is the ikG for that specific thi macroblock. In our case for this purpose a fast and simple cryptographic scheme can be utilized given that the requirements of the security for video watermarking systems are less than those of cryptographic systems. At this point we use a shift cipher with modulus 2 that is to say the plaintext ikP , and the kS . There are 2 bits of generated general key ikG that determine the selected 88 block in the macroblock. There are also other 2 bits that determine the selected 44 block in the 88 block. For watermark embedding process, the iA which is the selected AC coefficient in that 44 block is determined by a sum of 4 bits. Some characteristics in the MB are so delicate to the point that once they are tempered with slightly in a disanized manner, the quality perception of the video sequence must degrade. It is these characteristics then that the kP should be extracted. In case the atta