Departamento de Tecnologías de las Comunicaciones, E.T.S.I. Telecomunicación, Universidad de Vigo, Vigo 36200, Pontevedra, Spain.
IEEE Trans Image Process. 2000;9(1):55-68. doi: 10.1109/83.817598.
In this paper, a spread-spectrum-like discrete cosine transform (DCT) domain watermarking technique for copyright protection of still digital images is analyzed. The DCT is applied in blocks of 8x8 pixels, as in the JPEG algorithm. The watermark can encode information to track illegal misuses. For flexibility purposes, the original image is not necessary during the ownership verification process, so it must be modeled by noise. Two tests are involved in the ownership verification stage: watermark decoding, in which the message carried by the watermark is extracted, and watermark detection, which decides whether a given image contains a watermark generated with a certain key. We apply generalized Gaussian distributions to statistically model the DCT coefficients of the original image and show how the resulting detector structures lead to considerable improvements in performance with respect to the correlation receiver, which has been widely considered in the literature and makes use of the Gaussian noise assumption. As a result of our work, analytical expressions for performance measures, such as the probability of errors in watermark decoding and the probabilities of false alarms and of detection in watermark detection, are derived and contrasted with experimental results.
本文分析了一种用于保护静止数字图像版权的基于离散余弦变换 (DCT) 域的扩频类数字水印技术。DCT 以 JPEG 算法中 8x8 像素的块为单位进行应用。水印可以编码信息以跟踪非法滥用。出于灵活性的考虑，在所有权验证过程中不需要原始图像，因此必须对其进行噪声建模。所有权验证阶段涉及两个测试：水印解码，从中提取水印所携带的消息，以及水印检测，它决定给定的图像是否包含使用特定密钥生成的水印。我们应用广义高斯分布对原始图像的 DCT 系数进行统计建模，并展示了所得检测器结构如何相对于文献中广泛考虑的、利用高斯噪声假设的相关接收机在性能方面带来显著改进。作为我们工作的结果，导出了性能度量的分析表达式，例如水印解码错误概率、水印检测中的误报概率和检测概率，并与实验结果进行了对比。
