The Optimization Of DCT Algorithm And Its Application In Digital Watermarking

Discrete cosine transform (DCT) are widely used, and adopted by international standards such as JPEG,MPEG-1,MPEG-2, MPEG-4 and H.26x and so on.2D-DCT can be achieved by the two 1D-DCT,for the image block of 8 by 8, a new search algorithm was designed by the structural characteristics of the coefficient matraic of the DCT rank decomposition algorithm. Using values from the input data to determine the scope of addressing, each address stored in product value of the number of addresses and the coefficient,The algorithm used the input data to find the address and the stored data(a total of 15169, about 30.4KB). And it also avoided multiplication and shifts, and needed additoins of 128(320)times to complete DCT of one-demensional(two-demensional). The second one-dimensional DCT result of the input data range increases, and is not an integer, this paper adopted a rounded approximation, simulation results show that this algorithm is correct and effective.Optimization of DCT algorithm is used to research on digital watermarking in this paper. Digital watermarking algorithm based on DC component of DCT used to lead to blocking effect and less of the amount of information can be embedded. This paper converted vector images (512×512) into a YCbCr format and 8×8 minutes blocks, and two-dimensional discrete cosine transform is done on each block of the three components, extract the DC coefficient of each block to form a matrix, every 10-digit of each element of this matrix can embed two bits watermark image data (128×128), when the encrypted watermark data is "00"(01,10,11),the corresponding 10-digit should be changed into a number mode 4 left 0 (1,2,3), DC coefficient modification hold on the scope of [-30,30], and 24567 bits watermark data can be embedded. This algorithm does not affect the statistical properties of the image, extracting the watermark does not require the source data, it is a blind watermark. Experiments proved that the algorithm is effective way to avoid the block effect, can resist cutting and filtering and other attacks.