  Single-pixel imaging (SPI) has attracted widespread attention because it
generally uses a non-pixelated photodetector and a digital micromirror device
(DMD) to acquire the object image. Since the modulated patterns seen from two
reflection directions of the DMD are naturally complementary, one can apply
complementary balanced measurements to greatly improve the measurement
signal-to-noise ratio and reconstruction quality. However, the balance between
two reflection arms significantly determines the quality of differential
measurements. In this work, we propose and demonstrate a simple secondary
complementary balancing mechanism to minimize the impact of the imbalance on
the imaging system. In our SPI setup, we used a silicon free-space balanced
amplified photodetector with 5 mm active diameter which could directly output
the difference between two optical input signals in two reflection arms. Both
simulation and experimental results have demonstrated that the use of secondary
complementary balancing can result in a better cancellation of direct current
components of measurements and a better image restoration quality.
