The Study on Digital watermarking Technology

• Main Authors: Chang-Ruey Lin, 林長瑞
• Other Authors: Ching-Huang Wei
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/37942939455976323178

碩士 === 國立高雄第一科技大學 === 電腦與通訊工程系 === 89 === We propose three watermarking methods in the thesis. The first method is that the pixel values in the lowest-frequency band of three-level discrete wavelet transform (DWT) for the host image are quantized and then the index of quantization of each pixel is changed for embedding watermark. The second method based on the region of interest (ROI) within a host image, that is chosen by the applicant for the request of image. Then the watermark is embedded in the ROI area of host image by changing the least significant bits of ROI-masked pixel value in the bands of DWT for each tile of the original image. The final watermarking method searches the largest ac coefficient within 3´3 left-up corner of each 8´8 DCT block of the host image and then selects one of eight 2-D cosine-wave patterns to be added to or subtracted from the 8´8 blocks of the original image for embedding the watermark. Besides, we test the performance of various methods using the robustness against several attacks that include JPEG lossy compression, mean filter, media filter, cropping, additive noise, and JPEG2000 compression. The first watermarking method is very simply and easily implemented. The second watermarking method is strongly robust against JPEG2000 compression and some cropping attacks. Against the attacks of JPEG lossy compress, mean filter, media filter, and additive noise attacks, the third watermarking method has good performance in the measure of similarity between the extracted watermark and the original watermark.