By constructing two phase-shifted fringe images and a flat image, the 2 + 1 phase-shifting algorithm can reduce the error caused by motion and realize real-time and high-resolution three-dimensional (3-D) measurement. However, the nonlinear gamma of the digital light processing and the ambient light will affect the light-field distribution of the flat image, and extensive experiments have shown that the distribution of the captured flat image is inconsistent with the DC component of the deformed patterns. Therefore, based on the linear calibration model, a more realistic DC component of the deformed patterns is deduced from the captured flat image. The AC components of the deformed patterns can be extracted more genuinely by subtracting the deduced DC component from deformed patterns. So, the influence of ambient light can be suppressed efficiently to improve 3-D measuring accuracy. The experimental results show the feasibility and validity of the proposed method.