We can successfully solve the problem in DFD display that the maximum depth difference of front and rear planes is limited because depth fusing from front and rear images to one 3-D image becomes impossible. The range of continuously perceived depth was estimated as depth difference of front and rear planes increases. When the distance was large enough, perceived depth was near front plane at 0~40 % of rear luminance and near rear plane at 60~100 % of rear luminance. This maximum depth range can be successfully enlarged by spatial-frequency modulation of front and rear images. The change of perceived depth dependence was evaluated when high frequency component of front and rear images is cut off using Fourier Transformation at the distance between front and rear plane of 5 and 10 cm (4.9 and 9.4 minute of arc). When high frequency component does not cut off enough at the distance of 5 cm, perceived depth was separated to near front plane and near rear plane. However, when the images are blurred enough by cutting high frequency component, the perceived depth has a linear dependency on luminance ratio. When the images are not blurred at the distance of 10 cm, perceived depth is separated to near front plane at 0~30% of rear luminance, near rear plane at 80~100 % and near midpoint at 40~70 %. However, when the images are blurred enough, perceived depth successfully has a linear dependency on luminance ratio.