Imperceptibility of embedded digital watermark reflects the fidelity of watermarked image. The masking of frequency

luminance

texture and color on human vision were analyzed. Based on the color masking and Watson’s JND（just noticeable differences） model

a calculation method of JNCD（just noticeable color differences） for color image was proposed. Then the masking weight for each element of color image was calculated using the JNCD. A new imper- ceptibility measure of watermark in watermarked color image was proposed based on these masking weights

i.e. CPSNR （color image peak signal to noise ratio）. Experimental results show that the quality of watermarked color image calculated by CPSNR is the same as the result judged by human vision

and CPSNR can be used to evaluate the imperceptibility of watermarking methods.