A steganographic scheme with a very good visual quality of stego images was
proposed by Zhang and Wang. However, the maximum hiding capacity of this method is
1 bit per pixel (bpp). To improve the hiding capacity of Zhang and Wang's method, we
propose a steganographic scheme. The proposed method embeds 2K secret digits in the
5-ary notational systems into each group of (2K + 1) cover pixels, where K is a positive
integer. Thus, the maximum hiding capacity of the proposed method can approach 2 bpp.
The experimental results show that the PSNR values of the proposed method are always
higher than 45 dB at the hiding capacity of 1.99 bpp for all test images.
