A watermark is embedded into a color image. The relationship between embedding and compression process is investigated. The compression ratio (CR) is adjusted from 2 to 15, and three gray-levels of the original image are changed, their average gray-levels are individually 126, 161 and 196. From the experimental results, there is an apparent inclination about higher gray-level makes higher PSNR. There are two kinds of compression methods in the compression process, one includes color space transform and sampling, and this method has higher CR, the other has not these steps and it has lower CR. In this paper the relationship of these parameters such as the gray-level of the image, the parameters of frequency domain are also discussed and analyzed. The relation between color saturation and normalized correlation (NC) ratio has been quantitatively analyzed, it is found that the extracted watermark has the best quality when the saturation factor is set to the value of 0.2, and the NC value is lower when the processing has lower color factor. The curve of NC drops gradually when the color factor is over 0.4. The main reason of this result is also discussed in the final discussion. In our proposed approach, a systematic analysis is performed. The adaptive methods are selected to obtain the optimum conditions to embed the watermark into an image.
An analytic method of embedding color watermarks into the color images is proposed. The original image is color image of size 480X640, and the watermark image is 24-bit-gray scale image of size 120X160. The quality variations of the embedded image and extracted watermark are analyzed. From the experimental results they appear that the quality of embedded image varies with the quantization index (QI). They also show that the quality of extracted watermark is dependent on the gray-level of the original image. The relationship between the gray-level and the noise of embedded image has been quantitatively analyzed. The digital quantization method is also important to decrease the noise of embedding image and the error of extracting watermark.