DC - AC Coefficients based Multiple Watermarking Technique

DC coefficient based watermarking schemes are known for good robustness against common image processing operations. This paper use scheme based on Quantization Index Modulation (QIM) in which both DC and AC coefficients are quantized for watermark embedding. The purpose is to increase the embedding capacity while maintaining constant robustness. Step size of quantizer decides robustness in QIM based methods. For this work, step size is decided based on the frequency content of an image. It results in increased robustness for fixed capacity or vice versa.