Gain measurement method for CMOS detectors based on a modified photon transfer curve

The Earth 2.0 (ET) mission requires extreme image quality and photometric stability from its scientific CMOS detector, relying on precise photon transfer curve (PTC) gain calibration. Traditional PTC methods ignores nonlinear response and fixed-pattern noise, which introduces systematic errors—especially under low-light conditions and across the full dynamic range. To overcome this, we propose an improved PTC-based gain calculation method. A highly stable monochromatic light source first calibrates the nonlinear response, enabling a pre-correction that removes associated bias. Pixel-level temporal variance analysis is also applied to suppress fixed-pattern noise in PTC fitting. Simulations and experiments confirm that this method significantly improves detector characterization confidence and offers more accurate gain results. The approach provides a reliable theoretical foundation for developing and evaluating ultra-high-precision space imaging systems.