In order to solve the problem of direction discrimination and low-speed measurement for a spatial filtering velocimeter, a method of frequency shifting is put forward. The filtering device is constructed by a CMOS linear image sensor that is employed both as a differential spatiotemporal filter and as a photodetector. Frequency shifting is realized by shifting the pixels of the image sensor, and the shifting is implemented digitally. The power spectrum of the output signal is obtained by fast Fourier transform (FFT). Given the limited resolution of FFT, a frequency spectrum correction algorithm, called energy centrobaric correction, is utilized to improve the frequency resolution. The built system is used to measure the transverse velocity of a simple pendulum. The results of theory analysis and experiments verify the feasibility of direction discrimination and low-speed measurement by the method of frequency shifting. Experimental results also show that the method of energy centrobaric correction can improve the velocity resolution by more than one order of magnitude.