Effect of Spot Color on Extraction Quality of Holographic Watermark

To transplant the digital watermark into the field of packaging and printing anti-counterfeiting, the robustness of watermarks in different color spaces and channels against spot color printing was investigated. Taking holographic watermarking algorithm in discrete wavelet transformation domain as an example, the watermarks were embedded into the B, C and spot color channels of the host image in the form of hologram, and the effects of simulated screening and color space conversion attacks on the invisibility and robustness of the watermarks in different channels were investigated. Experiments shown that although spot color printing improved the PSNR value of the watermarked images, it reduced the robustness of the watermark to the color space changing attack, and the robustness of embedding the watermark in the spot color channel was the lowest. Spot color had different effects on different color spaces and color channels. It was suggested to embed watermark in the non-spot-color channel of CMYK color mode.