An electron multiplication charge-coupled device (EMCCD) and microchannel plate (MCP) image intensifier use high-voltage electric fields to multiply electrons after photoelectric conversion and photoelectrons converted from photocathode materials, respectively. The photo-electronic amplification technology used in both devices introduces additional noise factor, resulting in a decrease of the signal-to-noise ratio (SNR). A scientific complementary metal-oxide-semiconductor (sCMOS) image sensor is a detector proposed in recent years that does not rely on external structures and achieves high sensitivity by optimizing the CMOS pixel process, pixel structure, and readout circuit noise level. This paper proposes a method of calculating the modulation transfer function (MTF) and SNR of low-light detectors based on their optical and electrical parameters. For the same number of incident photons, the SNR of sCMOS, MCP, EMCCD low-light detectors are 6.89, 3.53, and 9.67, respectively, when the integration time is 1.0 s. The comprehensive MTFs at the Nyquist frequency are 0.63, 0.13, and 0.48, respectively. The product of the SNR and MTF at the Nyquist frequency is used as the imaging quality standard to compare and analyze the theoretical characteristics and applicable fields of the three low-light detectors.