The aim of this paper is to propose an imperceptible wavelet-based watermarking scheme. In our scheme, we use variation to define the degree of transparence of coefficients of LL band and further determine transparent coefficients of HL3 and LH3 bands. Then, the watermark is embedded into those coefficients. In addition, the modular operation is utilized during watermark embedding. In the experimental results, we simulate some common attacks on the watermarked image. It is shown that our scheme is robust against most attacks; moreover, the watermarked image is highly imperceptible.