Digital Watermarking Algorithm in DCT Transform Domain for Color Images

This paper presents a digital watermarking algorithm for color images operating in the Discrete Cosine Transform (DCT) domain. The algorithm embeds watermark information into DCT coefficients by performing DCT transformation on color images. Implementation typically involves processing RGB channels separately or converting to YCbCr color space and embedding in luminance components. Through extraction of watermark information from DCT coefficients, image authentication and copyright protection can be achieved. The methodology includes selecting appropriate watermark embedding parameters (such as quantization steps, frequency band selection, and embedding strength) and extraction parameters. Key implementation steps involve: applying block-based DCT to image segments, modifying mid-frequency coefficients using quantization index modulation, and applying inverse DCT to reconstruct the watermarked image. The extraction process reverses these operations by comparing coefficient relationships in the transformed domain. Experimental results demonstrate that this algorithm exhibits strong robustness against common attacks including JPEG compression, noise addition, and filtering operations. The technique effectively protects color image copyright and integrity while maintaining visual quality through optimized parameter selection and frequency domain coefficient manipulation.